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Publications of year 2002

Thesis

  1. Oliver Wolfgang Hirsch. Neue Verarbeitungsverfahren von Along-Track Interferometrie Daten eines Radars mit synthetischer Apertur. PhD thesis, Universität-Gesamthochschule Siegen, 2002. Keyword(s): SAR Processing, Along Track Interferometry, Interferometry, Airborne SAR.
    Abstract: The German remote sensing project EURoPAK-B is aimed at the development and the demonstration of a special remote sensing system for the measurement of ocean surface currents and the monitoring of underwater bottom topography in coastal waters on the basis of airborne along- track interferometric (ATI) synthetic aperture radar. In contrast to across-track interferometry ATI is directly sensitive to motions of the scatterers which have a radial velocity component. The ATI phase being directly proportional to the interferometric velocity contains not only contributions resulting from the effective ocean surface currents but also from effects like e. g. orbital motions of longer waves. Thus the actual surface ocean currents differ from the measured interferometric velocities. The processed ATI phase is the starting point for the determination of interferometric velocities and has to be handled accurately. Therefore some concepts concerning a very proper processing of ATI data have to be developed. This includes the correction of phase contributions resulting from the wave guide length at different channel frequencies. Another undesirable contribution to the phase results from the existing across-track component which depends on the squint angle during data acquisition. To minimize that effect the exact positions of the phase centres of both antennas have to be determined in a theoretical way. Also some other effects on the ATI data like the azimuthal displacement of moving targets have to be taken into account for a correct geolocation of the ATI data. This work gives also reasons why the ATI phase has to be unwrapped although the phase resulting from the ocean currents should be within the order of -PI and +PI. It will also been shown how phase unwrapping errors of the ATI phase can be removed. In this work these concepts for accurately processing ATI data are discussed and results are shown. Supplementary it points out the proposed remote sensing technique for accurate measurements of both ocean surface currents and underwater bottom topography in coastal waters generated by the University of Hamburg.

    @PhdThesis{hirsch:ati,
    Title = {{Neue Verarbeitungsverfahren von Along-Track Interferometrie Daten eines Radars mit synthetischer Apertur}},
    Author = {Oliver Wolfgang Hirsch},
    Year = {2002},
    Abstract = {The German remote sensing project EURoPAK-B is aimed at the development and the demonstration of a special remote sensing system for the measurement of ocean surface currents and the monitoring of underwater bottom topography in coastal waters on the basis of airborne along- track interferometric (ATI) synthetic aperture radar. In contrast to across-track interferometry ATI is directly sensitive to motions of the scatterers which have a radial velocity component. The ATI phase being directly proportional to the interferometric velocity contains not only contributions resulting from the effective ocean surface currents but also from effects like e. g. orbital motions of longer waves. Thus the actual surface ocean currents differ from the measured interferometric velocities. The processed ATI phase is the starting point for the determination of interferometric velocities and has to be handled accurately. Therefore some concepts concerning a very proper processing of ATI data have to be developed. This includes the correction of phase contributions resulting from the wave guide length at different channel frequencies. Another undesirable contribution to the phase results from the existing across-track component which depends on the squint angle during data acquisition. To minimize that effect the exact positions of the phase centres of both antennas have to be determined in a theoretical way. Also some other effects on the ATI data like the azimuthal displacement of moving targets have to be taken into account for a correct geolocation of the ATI data. This work gives also reasons why the ATI phase has to be unwrapped although the phase resulting from the ocean currents should be within the order of -PI and +PI. It will also been shown how phase unwrapping errors of the ATI phase can be removed. In this work these concepts for accurately processing ATI data are discussed and results are shown. Supplementary it points out the proposed remote sensing technique for accurate measurements of both ocean surface currents and underwater bottom topography in coastal waters generated by the University of Hamburg.},
    Keywords = {SAR Processing, Along Track Interferometry, Interferometry, Airborne SAR},
    Pdf = {../../../docs/hirsch.pdf},
    School = {Universit{\"a}t-Gesamthochschule Siegen} 
    }
    


Articles in journal or book chapters

  1. Andrea Bellettini and M. A. Pinto. Theoretical accuracy of synthetic aperture sonar micronavigation using a displaced phase-center antenna. IEEE Journal of Oceanic Engineering, 27(4):780-789, October 2002. Keyword(s): Synthetic Aperture Sonar, SAS, navigation, synthetic aperture sonar, 118 to 182 kHz, Cramer-Rao lower bound, array gain, beampattern specification, displaced phase-center antenna, DPCA, ping-to-ping cross-track displacement, sway, synthetic aperture sonar micronavigation, yaw, Antenna theory, Aperture antennas, Backscatter, Computational modeling, Counting circuits, Helium, Predictive models, Principal component analysis, Sonar navigation, Synthetic aperture sonar.
    Abstract: The Cramer-Rao lower bounds on the cross-track translation and rotation of a displaced phase-center antenna (DPCA) in the slant range plane between two successive pings (known as DPCA sway and yaw in what follows) are computed, assuming statistically homogeneous backscatter. These bounds are validated using experimental data from a 118-182-kHz sonar, showing an accuracy of the order of 20 microns on the ping-to-ping cross-track displacements. Next, the accuracy required on the DPCA sway and yaw in order to achieve a given synthetic aperture sonar (SAS) beampattern specification, specified by the expected SAS array gain, is computed as a function of the number P of pings in the SAS. Higher accuracy is required when P increases to counter the accumulation of errors during the integration of the elementary ping-to-ping estimates: the standard deviation must decrease as P-12/ for the DPCA sway and P-32/ for the yaw. Finally, by combining the above results, the lower bounds on DPCA micronavigation accuracy are established. These bounds set an upper limit to the SAS length achievable in practice. The maximum gain Q in cross-range resolution achievable by a DPCA micronavigated SAS is computed as a function of the key SAS parameters. These theoretical predictions are compared with simulations and experimental results.

    @Article{bellettiniPintoJOE2002TheoreticalAccuracySASonarMicronavigationDPCA,
    author = {Andrea Bellettini and M. A. Pinto},
    title = {Theoretical accuracy of synthetic aperture sonar micronavigation using a displaced phase-center antenna},
    journal = {IEEE Journal of Oceanic Engineering},
    year = {2002},
    volume = {27},
    number = {4},
    pages = {780-789},
    month = {Oct},
    issn = {0364-9059},
    abstract = {The Cramer-Rao lower bounds on the cross-track translation and rotation of a displaced phase-center antenna (DPCA) in the slant range plane between two successive pings (known as DPCA sway and yaw in what follows) are computed, assuming statistically homogeneous backscatter. These bounds are validated using experimental data from a 118-182-kHz sonar, showing an accuracy of the order of 20 microns on the ping-to-ping cross-track displacements. Next, the accuracy required on the DPCA sway and yaw in order to achieve a given synthetic aperture sonar (SAS) beampattern specification, specified by the expected SAS array gain, is computed as a function of the number P of pings in the SAS. Higher accuracy is required when P increases to counter the accumulation of errors during the integration of the elementary ping-to-ping estimates: the standard deviation must decrease as P-12/ for the DPCA sway and P-32/ for the yaw. Finally, by combining the above results, the lower bounds on DPCA micronavigation accuracy are established. These bounds set an upper limit to the SAS length achievable in practice. The maximum gain Q in cross-range resolution achievable by a DPCA micronavigated SAS is computed as a function of the key SAS parameters. These theoretical predictions are compared with simulations and experimental results.},
    doi = {10.1109/JOE.2002.805096},
    keywords = {Synthetic Aperture Sonar, SAS, navigation;synthetic aperture sonar;118 to 182 kHz;Cramer-Rao lower bound;array gain;beampattern specification;displaced phase-center antenna;DPCA,ping-to-ping cross-track displacement;sway;synthetic aperture sonar micronavigation;yaw;Antenna theory;Aperture antennas;Backscatter;Computational modeling;Counting circuits;Helium;Predictive models;Principal component analysis;Sonar navigation;Synthetic aperture sonar},
    owner = {ofrey},
    
    }
    


  2. P. Berardino, G. Fornaro, R. Lanari, and E. Sansosti. A new algorithm for surface deformation monitoring based on small baseline differential SAR interferograms. IEEE Transactions on Geoscience and Remote Sensing, 40(11):2375-2383, November 2002. Keyword(s): SAR Processing, SBAS, small baseline differential SAR interferometry, DInSAR, InSAR, SAR Interferometry, Campi Flegrei caldera, European Remote Sensing satellites, Italy, Naples, SAR interferometry, atmospheric phase artifacts filtering, differential synthetic aperture radar interferometry algorithm, ground deformations, independent SAR acquisition datasets, singular value decomposition method, spatial information, surface deformation monitoring algorithm, temporal evolution, temporal information, Earth crust, radiowave interferometry, remote sensing by radar, synthetic aperture radar, tectonics, volcanology.
    Abstract: We present a new differential synthetic aperture radar (SAR) interferometry algorithm for monitoring the temporal evolution of surface deformations. The presented technique is based on an appropriate combination of differential interferograms produced by data pairs characterized by a small orbital separation (baseline) in order to limit the spatial decorrelation phenomena. The application of the singular value decomposition method allows us to easily link independent SAR acquisition datasets, separated by large baselines, thus increasing the observation temporal sampling rate. The availability of both spatial and temporal information in the processed data is used to identify and filter out atmospheric phase artifacts. We present results obtained on the data acquired from 1992 to 2000 by the European Remote Sensing satellites and relative to the Campi Flegrei caldera and to the city of Naples, Italy, that demonstrate the capability of the proposed approach to follow the dynamics of the detected deformations.

    @Article{berardinoFornaroLanariSansostiTGARS2002SBAS,
    author = {Berardino, P. and Fornaro, G. and Lanari, R. and Sansosti, E.},
    title = {A new algorithm for surface deformation monitoring based on small baseline differential {SAR} interferograms},
    journal = {IEEE Transactions on Geoscience and Remote Sensing},
    year = {2002},
    volume = {40},
    number = {11},
    pages = {2375-2383},
    month = nov,
    issn = {0196-2892},
    abstract = {We present a new differential synthetic aperture radar (SAR) interferometry algorithm for monitoring the temporal evolution of surface deformations. The presented technique is based on an appropriate combination of differential interferograms produced by data pairs characterized by a small orbital separation (baseline) in order to limit the spatial decorrelation phenomena. The application of the singular value decomposition method allows us to easily link independent SAR acquisition datasets, separated by large baselines, thus increasing the observation temporal sampling rate. The availability of both spatial and temporal information in the processed data is used to identify and filter out atmospheric phase artifacts. We present results obtained on the data acquired from 1992 to 2000 by the European Remote Sensing satellites and relative to the Campi Flegrei caldera and to the city of Naples, Italy, that demonstrate the capability of the proposed approach to follow the dynamics of the detected deformations.},
    doi = {10.1109/TGRS.2002.803792},
    keywords = {SAR Processing, SBAS, small baseline differential SAR interferometry; DInSAR, InSAR, SAR Interferometry, Campi Flegrei caldera; European Remote Sensing satellites; Italy; Naples; SAR interferometry; atmospheric phase artifacts filtering; differential synthetic aperture radar interferometry algorithm; ground deformations; independent SAR acquisition datasets; singular value decomposition method; spatial information; surface deformation monitoring algorithm; temporal evolution; temporal information; Earth crust; radiowave interferometry; remote sensing by radar; synthetic aperture radar; tectonics; volcanology},
    
    }
    


  3. H.L. Chan and T.S. Yeo. Non-iterative quality phase-gradient autofocus (QPGA) algorithm for spotlight SAR imagery. IEEE Trans. Geosci. Remote Sens., 40(11):2517, November 2002. Keyword(s): SAR Processing, Autofocus, Phase Gradient Autofocus, Quality Phase Gradient Autofocus, QPGA.
    Abstract: The quality phase-gradient autofocus (QPGA) technique was proposed to speed up the estimation convergence of phase-gradient autofocus by selectively increasing the pool of quality synchronization sources instead of selecting the brightest pixels within the image. It is now found hat the QPGA, with its inherent scatter growing- concept and target-filtering procedure, is also able to focus in environments with stationary and moving targets.

    @Article{Chan2002,
    Title = {Non-iterative quality phase-gradient autofocus (QPGA) algorithm for spotlight SAR imagery},
    Author = {Chan, H.L. and Yeo, T.S.},
    Month = nov,
    Number = {11},
    Pages = {2517},
    Volume = {40},
    Year = {2002},
    Abstract = {The quality phase-gradient autofocus (QPGA) technique was proposed to speed up the estimation convergence of phase-gradient autofocus by selectively increasing the pool of quality synchronization sources instead of selecting the brightest pixels within the image. It is now found hat the QPGA, with its inherent scatter growing- concept and target-filtering procedure, is also able to focus in environments with stationary and moving targets.},
    Journal = {IEEE Trans. Geosci. Remote Sens.},
    Keywords = {SAR Processing, Autofocus, Phase Gradient Autofocus, Quality Phase Gradient Autofocus, QPGA},
    Owner = {ofrey},
    Pdf = {../../../docs/chanYeo2002.pdf} 
    }
    


  4. Curtis W. Chen and Howard A. Zebker. Phase unwrapping for large SAR interferograms: statistical segmentation and generalized network models. IEEE Trans. Geosci. Remote Sens., 40(8):1709-1719, August 2002. Keyword(s): SAR Processing, phase unwrapping, SNAPHU, geophysical signal processing, image segmentation, optimisation, radar imaging, radiowave interferometry, remote sensing by radar, statistical analysis, synthetic aperture radar, InSAR data, SNAPHU, a posteriori probability, central Alaska, full-size interferograrn, generalized network models, interferometric input data, interferometric synthetic aperture radar data, large SAR interferograms, network-flow, nonlinear solver, phase unwrapping, secondary optimization problem, statistical models, statistical segmentation, statistical-cost network-flow phase-unwrapping algorithm, tile-unwrapping stage, tiles, topographic interferogram, Algorithm design and analysis, Data analysis, Geophysics computing, Partitioning algorithms, Phase estimation, Probability, Synthetic aperture radar interferometry, Two dimensional displays.
    Abstract: Two-dimensional (2-D) phase unwrapping is a key step in the analysis of interferometric synthetic aperture radar (InSAR) data. While challenging even in the best of circumstances, this problem poses unique difficulties when the dimensions of the interferometric input data exceed the limits of one's computational capabilities. In order to deal with such cases, we propose a technique for applying the statistical-cost, network-flow phase-unwrapping algorithm (SNAPHU) of Chen and Zebker (2001) to large datasets. Specifically, we introduce a methodology whereby a large interferogram is partitioned into a set of several smaller tiles that are unwrapped individually and then divided further into independent, irregularly shaped reliable regions. These regions are subsequently assembled into a full unwrapped solution, with the phase offsets between regions computed in a secondary optimization problem whose objective is to maximize the a posteriori probability of the final solution. As this secondary problem assumes the same statistical models as employed in the initial tile-unwrapping stage, the technique results in a solution that approximates the solution that would have been obtained had the full-size interferogram been unwrapped as a single piece. The secondary problem is framed in terms of network-flow ideas, allowing the use of an existing nonlinear solver. Applying the algorithm to a large topographic interferogram acquired over central Alaska, we find that the technique is less prone to unwrapping artifacts than more simple tiling approaches.

    @Article{chenZebkerTGRS2002SNAPHUPhaseUnwrappingForLargeSARInterferograms,
    author = {Curtis W. Chen and Howard A. Zebker},
    title = {Phase unwrapping for large SAR interferograms: statistical segmentation and generalized network models},
    journal = {IEEE Trans. Geosci. Remote Sens.},
    year = {2002},
    volume = {40},
    number = {8},
    pages = {1709-1719},
    month = aug,
    issn = {0196-2892},
    abstract = {Two-dimensional (2-D) phase unwrapping is a key step in the analysis of interferometric synthetic aperture radar (InSAR) data. While challenging even in the best of circumstances, this problem poses unique difficulties when the dimensions of the interferometric input data exceed the limits of one's computational capabilities. In order to deal with such cases, we propose a technique for applying the statistical-cost, network-flow phase-unwrapping algorithm (SNAPHU) of Chen and Zebker (2001) to large datasets. Specifically, we introduce a methodology whereby a large interferogram is partitioned into a set of several smaller tiles that are unwrapped individually and then divided further into independent, irregularly shaped reliable regions. These regions are subsequently assembled into a full unwrapped solution, with the phase offsets between regions computed in a secondary optimization problem whose objective is to maximize the a posteriori probability of the final solution. As this secondary problem assumes the same statistical models as employed in the initial tile-unwrapping stage, the technique results in a solution that approximates the solution that would have been obtained had the full-size interferogram been unwrapped as a single piece. The secondary problem is framed in terms of network-flow ideas, allowing the use of an existing nonlinear solver. Applying the algorithm to a large topographic interferogram acquired over central Alaska, we find that the technique is less prone to unwrapping artifacts than more simple tiling approaches.},
    doi = {10.1109/TGRS.2002.802453},
    file = {:chenZebkerTGRS2002SNAPHUPhaseUnwrappingForLargeSARInterferograms.pdf:PDF},
    keywords = {SAR Processing, phase unwrapping, SNAPHU, geophysical signal processing;image segmentation;optimisation;radar imaging;radiowave interferometry;remote sensing by radar;statistical analysis;synthetic aperture radar;InSAR data;SNAPHU;a posteriori probability;central Alaska;full-size interferograrn;generalized network models;interferometric input data;interferometric synthetic aperture radar data;large SAR interferograms;network-flow;nonlinear solver;phase unwrapping;secondary optimization problem;statistical models;statistical segmentation;statistical-cost network-flow phase-unwrapping algorithm;tile-unwrapping stage;tiles;topographic interferogram;Algorithm design and analysis;Data analysis;Geophysics computing;Partitioning algorithms;Phase estimation;Probability;Synthetic aperture radar interferometry;Two dimensional displays},
    owner = {ofrey},
    
    }
    


  5. G. Fornaro and A.M. Guarnieri. Minimum mean square error space-varying filtering of interferometric SAR data. IEEE Transactions on Geoscience and Remote Sensing, 40(1):11 -21, January 2002. Keyword(s): SAR Processing, SAR Interferometry, DEM, Doppler centroid decorrelation, IFSAR, InSAR, algorithm, azimuth direction, digital elevation model, geometrical decorrelation, geophysical measurement technique, imaging, interferometric SAR, land surface, minimum mean square error method, nonplanar topography, radar remote sensing, scene topography, space varying filtering, space-variant, synthetic aperture radar, terrain mapping, geophysical signal processing, geophysical techniques, radar imaging, remote sensing by radar, synthetic aperture radar, terrain mapping.
    Abstract: This paper addresses the problem of filtering interferometric synthetic aperture radar (IFSAR) signals in presence of nonplanar topography to mitigate geometrical decorrelation effects. The problem is space-variant. The authors assume knowledge about the scene topography and derive an optimal, minimum mean square error (MMSE), filtering procedure. The algorithm is flexible and, beside the standard stripmap-stripmap interferometry, it may be applied to IFSAR data acquired in any operative mode. For instance, in scan-scan, scan-strip, and scan-spot interferometry. The scene topography contribution may be either derived from an external rough digital elevation model (DEM) or directly estimated from the SAR data. The filtering technique is extended to the azimuth direction to account for possible Doppler centroid decorrelation. Experimental results carried out on real data confirm the validity of the theory and show that this filtering procedure allows the authors to obtain a reduction of the interferometric noise content. Its gain is particularly marked in the cases of steep topography, where application of the standard common band filters could deteriorate the signal quality, or for large Doppler centroid shifts between the two acquisitions

    @Article{981345,
    Title = {Minimum mean square error space-varying filtering of interferometric SAR data},
    Author = {Fornaro, G. and Guarnieri, A.M.},
    Doi = {10.1109/36.981345},
    ISSN = {0196-2892},
    Month = jan,
    Number = {1},
    Pages = {11 -21},
    Volume = {40},
    Year = {2002},
    Abstract = {This paper addresses the problem of filtering interferometric synthetic aperture radar (IFSAR) signals in presence of nonplanar topography to mitigate geometrical decorrelation effects. The problem is space-variant. The authors assume knowledge about the scene topography and derive an optimal, minimum mean square error (MMSE), filtering procedure. The algorithm is flexible and, beside the standard stripmap-stripmap interferometry, it may be applied to IFSAR data acquired in any operative mode. For instance, in scan-scan, scan-strip, and scan-spot interferometry. The scene topography contribution may be either derived from an external rough digital elevation model (DEM) or directly estimated from the SAR data. The filtering technique is extended to the azimuth direction to account for possible Doppler centroid decorrelation. Experimental results carried out on real data confirm the validity of the theory and show that this filtering procedure allows the authors to obtain a reduction of the interferometric noise content. Its gain is particularly marked in the cases of steep topography, where application of the standard common band filters could deteriorate the signal quality, or for large Doppler centroid shifts between the two acquisitions},
    Journal = {IEEE Transactions on Geoscience and Remote Sensing},
    Keywords = {SAR Processing, SAR Interferometry, DEM;Doppler centroid decorrelation;IFSAR;InSAR;algorithm;azimuth direction;digital elevation model;geometrical decorrelation;geophysical measurement technique;imaging;interferometric SAR;land surface;minimum mean square error method;nonplanar topography;radar remote sensing;scene topography;space varying filtering;space-variant;synthetic aperture radar;terrain mapping;geophysical signal processing;geophysical techniques;radar imaging;remote sensing by radar;synthetic aperture radar;terrain mapping} 
    }
    


  6. G. Fornaro, E. Sansosti, R. Lanari, and M. Tesauro. Role of processing geometry in SAR raw data focusing. IEEE Transactions on Aerospace and Electronic Systems, 38(2):441-454, April 2002. Keyword(s): SAR Processing, 2D frequency SAR processing, SAR raw data focusing, airborne remote sensing, conical reference systems, geometric artifacts, high-resolution images, high-resolution microwave images, interferometric SAR, microwave remote sensing, phase aberrations, processing geometry role, received backscattered echoes, space-invariant component, space-variant component, spaceborne remote sensing, squinted geometries, squinted raw data acquisitions, stripmap mode, airborne radar, image registration, radar imaging, radar resolution, remote sensing by radar, sensor fusion, spaceborne radar, synthetic aperture radar.
    Abstract: Synthetic aperture radar (SAR) systems require that a focusing operation be performed on the received backscattered echoes (raw data) to generate high-resolution microwave images. Either due to platform attitude instabilities, or to Earth rotation effects, the SAR raw data may be acquired squinted geometries, i.e., with the radar beam directed with an offset angle (squint angle) from the broadside direction. This research investigates the impact of the focusing operation carried out on squinted raw data acquisitions performed by SAR sensors operating in the stripmap mode. To this end the 2D frequency SAR processing approach is generalized with respect to conical, i.e., nonorthogonal, reference systems. This allows analysis of the geometric, spectral, and phase aberrations introduced in the images by the chosen processing geometry with respect to the acquisition, and identification of the focusing procedure that minimizes these aberrations. The whole theory is validated by experimental results carried out on simulated data. Moreover, the extension of this analysis to the interferometric case where these aberrations may have a significant role is also investigated

    @Article{fornaroSansostiLanariTesauro2002:ProcessingGeometrySAR,
    Title = {Role of processing geometry in {SAR} raw data focusing},
    Author = {Fornaro, G. and Sansosti, E. and Lanari, R. and Tesauro, M.},
    Doi = {10.1109/TAES.2002.1008978},
    ISSN = {0018-9251},
    Month = apr,
    Number = {2},
    Pages = {441-454},
    Url = {http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=1008978},
    Volume = {38},
    Year = {2002},
    Abstract = {Synthetic aperture radar (SAR) systems require that a focusing operation be performed on the received backscattered echoes (raw data) to generate high-resolution microwave images. Either due to platform attitude instabilities, or to Earth rotation effects, the SAR raw data may be acquired squinted geometries, i.e., with the radar beam directed with an offset angle (squint angle) from the broadside direction. This research investigates the impact of the focusing operation carried out on squinted raw data acquisitions performed by SAR sensors operating in the stripmap mode. To this end the 2D frequency SAR processing approach is generalized with respect to conical, i.e., nonorthogonal, reference systems. This allows analysis of the geometric, spectral, and phase aberrations introduced in the images by the chosen processing geometry with respect to the acquisition, and identification of the focusing procedure that minimizes these aberrations. The whole theory is validated by experimental results carried out on simulated data. Moreover, the extension of this analysis to the interferometric case where these aberrations may have a significant role is also investigated},
    Journal = {IEEE Transactions on Aerospace and Electronic Systems},
    Keywords = {SAR Processing, 2D frequency SAR processing;SAR raw data focusing;airborne remote sensing; conical reference systems;geometric artifacts;high-resolution images;high-resolution microwave images; interferometric SAR;microwave remote sensing;phase aberrations;processing geometry role; received backscattered echoes;space-invariant component;space-variant component;spaceborne remote sensing; squinted geometries;squinted raw data acquisitions;stripmap mode;airborne radar;image registration; radar imaging;radar resolution;remote sensing by radar;sensor fusion;spaceborne radar;synthetic aperture radar},
    Pdf = {../../../docs/fornaroSansostiLanariTesauro2002.pdf} 
    }
    


  7. Per-Olov Frölind and Lars M. H. Ulander. Digital Elevation Map Generation Using VHF-Band SAR Data in Forested Areas. IEEE Transactions on Geoscience and Remote Sensing, 40(8):1769-1776, August 2002. Keyword(s): SAR Processing, Interferometry, DEM Generation, Time-Domain Back-Projection, Backprojection, Ultra-Wideband SAR, VHF SAR, CARABAS, Airborne SAR.
    Abstract: The paper investigates digital elevation model (DEM) generation based on data from the ultra wideband coherent all radio band sensing (CARABAS) very high frequency (VRF)-band synthetic aperture radar (SAR). The results show excellent capability to penetrate forest areas, i.e., the generated DEMs are found to be close to the true ground height. A conventional DEM, based on stereo photography and surveying, and additional phase differential Global Positioning System (GPS) measurements have been used for comparison. The results in heavily vegetated areas (stem volume up to 600 m^3/ha) show a mean height difference of less than 1.5 m and a root-mean-square (rms) error of less than 1.0 in compared to the conventional DEM. Stable backscattering properties allows us to use large baselines in order to obtain high height sensitivity. However, the amount of poor data due to low coherence increases with the increase of the baseline. The optimum baseline which balances these two effects is found to correspond to an incidence angle difference of 4 deg - 8 deg.

    @Article{froelindUlander02:Interfero,
    Title = {{Digital Elevation Map Generation Using VHF-Band SAR Data in Forested Areas}},
    Author = {Per-Olov Fr{\"o}lind and Lars M. H. Ulander},
    Month = Aug,
    Number = {8},
    Pages = {1769-1776},
    Url = {http://ieeexplore.ieee.org/iel5/36/22230/01036005.pdf},
    Volume = {40},
    Year = {2002},
    Abstract = {The paper investigates digital elevation model (DEM) generation based on data from the ultra wideband coherent all radio band sensing (CARABAS) very high frequency (VRF)-band synthetic aperture radar (SAR). The results show excellent capability to penetrate forest areas, i.e., the generated DEMs are found to be close to the true ground height. A conventional DEM, based on stereo photography and surveying, and additional phase differential Global Positioning System (GPS) measurements have been used for comparison. The results in heavily vegetated areas (stem volume up to 600 m^3/ha) show a mean height difference of less than 1.5 m and a root-mean-square (rms) error of less than 1.0 in compared to the conventional DEM. Stable backscattering properties allows us to use large baselines in order to obtain high height sensitivity. However, the amount of poor data due to low coherence increases with the increase of the baseline. The optimum baseline which balances these two effects is found to correspond to an incidence angle difference of 4 deg - 8 deg.},
    Journal = {IEEE Transactions on Geoscience and Remote Sensing},
    Keywords = {SAR Processing, Interferometry, DEM Generation, Time-Domain Back-Projection, Backprojection, Ultra-Wideband SAR, VHF SAR, CARABAS, Airborne SAR},
    Pdf = {../../../docs/froelindUlander02.pdf} 
    }
    


  8. Dirk Geudtner, Manfred Zink, Christoph Gierull, and Scott Shaffer. Interferometric Alignment of the X-SAR Antenna System on the Space Shuttle Radar Topography Mission. IEEE Transactions on Geoscience and Remote Sensing, 40(5):995-1006, May 2002. Keyword(s): SAR Processing, Antenna Beam Alignment, Interferometry, SRTM, X-SAR.
    Abstract: The on-orbit alignment of the antenna beams of both the X-band and C-band radar systems during operations of the shuttle radar topography mission/X-band synthetic aperture radar (SRTM/X-SAR) was a key requirement for achieving best interferometric performance. In this paper, we consider the X-SAR antenna beam alignment in azimuth. For a single-pass cross-track SAR interferometer, we establish the relation between yaw and pitch misalignment of the antenna beams and the resulting relative shift of the Doppler frequency bands. This relation is used to provide solutions for the mechanical adjustments of the outboard antenna and electronic beam steering to correct for azimuth misalignment. Furthermore, the effects of the X-SAR effective outboard antenna pattern on the azimuth beam alignment are analyzed. As a result, a so-called relaxing factor is derived, which increases the limit for the difference in antenna azimuth angle with respect to the requirement on spectral overlap, and hence spatial interferogram resolution. However, we also show that the alignment requirement is driven by the constraint on decreasing the azimuth ambiguity-to-signal ratio (AASR) for the effective outboard antenna pattern to reduce the resulting additional height error. The strategy for misalignment determination and correction is presented, and results of the analysis of the in-flight X-SAR antenna beam alignment are discussed.

    @Article{geudtnerZink02:SRTM,
    Title = {{Interferometric Alignment of the X-SAR Antenna System on the Space Shuttle Radar Topography Mission}},
    Author = {Dirk Geudtner and Manfred Zink and Christoph Gierull and Scott Shaffer},
    Month = May,
    Number = {5},
    Pages = {995-1006},
    Volume = {40},
    Year = {2002},
    Abstract = {The on-orbit alignment of the antenna beams of both the X-band and C-band radar systems during operations of the shuttle radar topography mission/X-band synthetic aperture radar (SRTM/X-SAR) was a key requirement for achieving best interferometric performance. In this paper, we consider the X-SAR antenna beam alignment in azimuth. For a single-pass cross-track SAR interferometer, we establish the relation between yaw and pitch misalignment of the antenna beams and the resulting relative shift of the Doppler frequency bands. This relation is used to provide solutions for the mechanical adjustments of the outboard antenna and electronic beam steering to correct for azimuth misalignment. Furthermore, the effects of the X-SAR effective outboard antenna pattern on the azimuth beam alignment are analyzed. As a result, a so-called relaxing factor is derived, which increases the limit for the difference in antenna azimuth angle with respect to the requirement on spectral overlap, and hence spatial interferogram resolution. However, we also show that the alignment requirement is driven by the constraint on decreasing the azimuth ambiguity-to-signal ratio (AASR) for the effective outboard antenna pattern to reduce the resulting additional height error. The strategy for misalignment determination and correction is presented, and results of the analysis of the in-flight X-SAR antenna beam alignment are discussed.},
    Journal = {IEEE Transactions on Geoscience and Remote Sensing},
    Keywords = {SAR Processing, Antenna Beam Alignment, Interferometry, SRTM, X-SAR},
    Pdf = {../../../docs/geudtnerZink02.pdf} 
    }
    


  9. Christoph H. Gierull and Ishuwa C. Sikaneta. Estimating the effective number of looks in interferometric SAR data. IEEE Trans. Geosci. Remote Sens., 40(8):1733-1742, August 2002. Keyword(s): SAR Processing, ENL, effective number of looks, maximum likelihood estimation, method of moments, radar imaging, radiowave interferometry, remote sensing by radar, synthetic aperture radar, CFAR detection thresholds, MoM, adjacent pixels, compensation, complex correlation coefficient, constant false alarm rate detection thresholds, effective number of looks, filtering, interferometric SAR data, maximum-likelihood estimator, method of moments, moving-target detection, multilook interferometric phase, pdf, probability density function, statistical dependence, synthetic aperture radar images, Clutter, Interferometry, Layout, Maximum likelihood estimation, Pixel, Probability density function, Radar detection, Speckle, Statistics.
    Abstract: The probability density function (pdf) of the multi-look interferometric phase between two complex synthetic aperture radar (SAR) images is parameterized by the number of looks and the complex correlation coefficient. In practice, adjacent pixels in a real SAR interferogram, are statistically dependent due to filtering, and hence, the number of looks is usually smaller than the number of samples averaged. It has been shown that compensation with an effective number of looks, rather than an intractable rederivation of the pdf, can account for the statistical dependence. This paper addresses the challenge of how to determine a suitable value for the effective number of looks. It is shown that an optimum value can be found via a maximum-likelihood estimator (MLE) based on the interferometric phase pdf. However, since such an MLE is computationally intensive and numerically unstable, an estimator based on the method of moments (MoM) possessing similar fidelity is proposed. MoM is fast and robust and can be used in operational applications, such as determining constant false alarm rate (CFAR) detection thresholds for moving-target detection in SAR along-track interferometry.

    @Article{gierullSikanetaTGRS2002EffectiveNumberOfLooks,
    author = {Gierull, Christoph H. and Sikaneta, Ishuwa C.},
    title = {Estimating the effective number of looks in interferometric {SAR} data},
    journal = {IEEE Trans. Geosci. Remote Sens.},
    year = {2002},
    volume = {40},
    number = {8},
    pages = {1733-1742},
    month = aug,
    issn = {0196-2892},
    abstract = {The probability density function (pdf) of the multi-look interferometric phase between two complex synthetic aperture radar (SAR) images is parameterized by the number of looks and the complex correlation coefficient. In practice, adjacent pixels in a real SAR interferogram, are statistically dependent due to filtering, and hence, the number of looks is usually smaller than the number of samples averaged. It has been shown that compensation with an effective number of looks, rather than an intractable rederivation of the pdf, can account for the statistical dependence. This paper addresses the challenge of how to determine a suitable value for the effective number of looks. It is shown that an optimum value can be found via a maximum-likelihood estimator (MLE) based on the interferometric phase pdf. However, since such an MLE is computationally intensive and numerically unstable, an estimator based on the method of moments (MoM) possessing similar fidelity is proposed. MoM is fast and robust and can be used in operational applications, such as determining constant false alarm rate (CFAR) detection thresholds for moving-target detection in SAR along-track interferometry.},
    doi = {10.1109/TGRS.2002.802457},
    file = {:gierullSikanetaTGRS2002EffectiveNumberOfLooks.pdf:PDF},
    keywords = {SAR Processing, ENL, effective number of looks, maximum likelihood estimation, method of moments, radar imaging, radiowave interferometry, remote sensing by radar, synthetic aperture radar, CFAR detection thresholds, MoM, adjacent pixels, compensation, complex correlation coefficient, constant false alarm rate detection thresholds, effective number of looks, filtering, interferometric SAR data, maximum-likelihood estimator, method of moments, moving-target detection, multilook interferometric phase, pdf, probability density function, statistical dependence, synthetic aperture radar images, Clutter, Interferometry, Layout, Maximum likelihood estimation, Pixel, Probability density function, Radar detection, Speckle, Statistics},
    pdf = {../../../docs/gierullSikanetaTGRS2002EffectiveNumberOfLooks.pdf},
    
    }
    


  10. F. Gini, F. Lombardini, and M. Montanari. Layover solution in multibaseline SAR interferometry. Aerospace and Electronic Systems, IEEE Transactions on, 38(4):1344-1356, 2002. Keyword(s): SAR Processing, SAR Tomography, Tomography, Monte Carlo methods, airborne radar, radiowave interferometry, remote sensing by radar, synthetic aperture radar, MUSIC, Cramer-Rao lower bounds, Interferometry, InSAR, M-RELAX, Monte Carlo simulations, RELAX algorithm, baseline diversity, discontinuities, height contributions, layover solution, multibaseline SAR interferometry, multichannel interferometric synthetic aperture radar, multiplicative noise, natural targets, nonparametric techniques, parametric techniques, range-azimuth resolution cell, spectral estimation techniques, terrain slopes.
    Abstract: In this work, spectral estimation techniques are used to exploit baseline diversity of a multichannel interferometric synthetic aperture radar (SAR) system and overcome the layover problem. This problem arises when different height contributions collapse in the same range-azimuth resolution cell, due to the presence of strong terrain slopes or discontinuities in the sensed scene. We propose a multilook approach to counteract the presence of multiplicative noise, which is due to the extended nature of natural targets; to this purpose we extend the RELAX algorithm to the multilook data scenario (M-RELAX). A thorough performance analysis of nonparametric (beamforming and Capon) and parametric (root MUSIC and M-RELAX) techniques is carried out based on Monte Carlo simulations and Cramer-Rao lower bounds (CRLB) calculation. The results suggest the superiority of parametric methods over nonparametric ones.

    @Article{giniLombardiniMontanari02:LayoverMultibaseline,
    Title = {Layover solution in multibaseline SAR interferometry},
    Author = {Gini, F. and Lombardini, F. and Montanari, M.},
    Number = {4},
    Pages = {1344--1356},
    Url = {http://ieeexplore.ieee.org/iel5/7/25794/01145755.pdf},
    Volume = {38},
    Year = {2002},
    Abstract = {In this work, spectral estimation techniques are used to exploit baseline diversity of a multichannel interferometric synthetic aperture radar (SAR) system and overcome the layover problem. This problem arises when different height contributions collapse in the same range-azimuth resolution cell, due to the presence of strong terrain slopes or discontinuities in the sensed scene. We propose a multilook approach to counteract the presence of multiplicative noise, which is due to the extended nature of natural targets; to this purpose we extend the RELAX algorithm to the multilook data scenario (M-RELAX). A thorough performance analysis of nonparametric (beamforming and Capon) and parametric (root MUSIC and M-RELAX) techniques is carried out based on Monte Carlo simulations and Cramer-Rao lower bounds (CRLB) calculation. The results suggest the superiority of parametric methods over nonparametric ones.},
    Journal = {Aerospace and Electronic Systems, IEEE Transactions on},
    Keywords = {SAR Processing, SAR Tomography, Tomography, Monte Carlo methods, airborne radar, radiowave interferometry, remote sensing by radar, synthetic aperture radar, MUSIC, Cramer-Rao lower bounds,Interferometry, InSAR, M-RELAX, Monte Carlo simulations, RELAX algorithm, baseline diversity, discontinuities, height contributions, layover solution, multibaseline SAR interferometry, multichannel interferometric synthetic aperture radar, multiplicative noise, natural targets, nonparametric techniques, parametric techniques, range-azimuth resolution cell, spectral estimation techniques, terrain slopes},
    Owner = {ofrey},
    Pdf = {../../../docs/giniLombardiniMontanari02.pdf} 
    }
    


  11. F. Gustrau and A. Bahr. W-band investigation of material parameters, SAR distribution, and thermal response in human tissue. IEEE Transactions on Microwave Theory and Techniques, 50(10):2393-2400, October 2002. Keyword(s): SAR Processing, W-Band, bioelectric phenomena, biological effects of microwaves, biological tissues, biothermics, dosimetry, eye, finite difference time-domain analysis, health hazards, infrared imaging, skin, 3 to 100 GHz, 77 GHz, Gunn oscillator, SAR distribution, W-band dielectric properties, analytical method, dosimetry, electromagnetic field, eye tissue, finite-difference time-domain method, horn antenna, human eye, human tissue, layered skin model, maximum local SAR values, maximum temperature increase, millimeter-wave irradiation, plane-wave exposure, porcine eye, safety guidelines, skin, specific absorption rate, superficial tissue, temperature changes, thermal bio-heat-transfer simulation, thermal infrared imaging system, thermal response, Antenna measurements, Biological materials, Biological system modeling, Biological tissues, Dielectric materials, Electromagnetic fields, Humans, Millimeter wave measurements, Skin, Temperature.
    Abstract: This investigation is divided into three parts. First, the W-band dielectric properties of different biological tissues are determined. Then, the electromagnetic field in the human eye and skin is simulated for plane-wave exposure. An analytical method is used to investigate the specific absorption rate (SAR) inside a layered model of the human skin between 3-100 GHz. Furthermore, the SAR inside a detailed model of the human eye is investigated numerically by the finite-difference time-domain method for a frequency of 77 GHz. Maximum local SAR values of 27.2 W/kg in skin tissue and 45.1 W/kg in eye tissue are found for 77 GHz and an incident power density of 1 mW/cm2. In the third part of the investigation, the temperature changes of superficial tissue caused by millimeter-wave irradiation are measured by a thermal infrared imaging system. The exposure setup is based on a horn antenna with a Gunn oscillator operating at 15.8-dBm output power. The measurements showed a maximum temperature increase of 0.7 deg C for a power density of 10 mW/cm2 and less than 0.1 deg C for 1 mW/cm2, both in human skin (in vivo), as well as in porcine eye (in vitro). The comparison of the temperature measurements with a thermal bio-heat-transfer simulation of a layered skin model showed a good agreement.

    @ARTICLE{gustrauBahrTMTT2002WBandSAR,
    author={F. Gustrau and A. Bahr},
    journal={IEEE Transactions on Microwave Theory and Techniques},
    title={W-band investigation of material parameters, SAR distribution, and thermal response in human tissue},
    year={2002},
    volume={50},
    number={10},
    pages={2393-2400},
    abstract={This investigation is divided into three parts. First, the W-band dielectric properties of different biological tissues are determined. Then, the electromagnetic field in the human eye and skin is simulated for plane-wave exposure. An analytical method is used to investigate the specific absorption rate (SAR) inside a layered model of the human skin between 3-100 GHz. Furthermore, the SAR inside a detailed model of the human eye is investigated numerically by the finite-difference time-domain method for a frequency of 77 GHz. Maximum local SAR values of 27.2 W/kg in skin tissue and 45.1 W/kg in eye tissue are found for 77 GHz and an incident power density of 1 mW/cm2. In the third part of the investigation, the temperature changes of superficial tissue caused by millimeter-wave irradiation are measured by a thermal infrared imaging system. The exposure setup is based on a horn antenna with a Gunn oscillator operating at 15.8-dBm output power. The measurements showed a maximum temperature increase of 0.7 deg C for a power density of 10 mW/cm2 and less than 0.1 deg C for 1 mW/cm2, both in human skin (in vivo), as well as in porcine eye (in vitro). The comparison of the temperature measurements with a thermal bio-heat-transfer simulation of a layered skin model showed a good agreement.},
    keywords={SAR Processing, W-Band,bioelectric phenomena;biological effects of microwaves;biological tissues;biothermics;dosimetry;eye;finite difference time-domain analysis;health hazards;infrared imaging;skin;3 to 100 GHz;77 GHz;Gunn oscillator;SAR distribution;W-band dielectric properties;analytical method;dosimetry;electromagnetic field;eye tissue;finite-difference time-domain method;horn antenna;human eye;human tissue;layered skin model;maximum local SAR values;maximum temperature increase;millimeter-wave irradiation;plane-wave exposure;porcine eye;safety guidelines;skin;specific absorption rate;superficial tissue;temperature changes;thermal bio-heat-transfer simulation;thermal infrared imaging system;thermal response;Antenna measurements;Biological materials;Biological system modeling;Biological tissues;Dielectric materials;Electromagnetic fields;Humans;Millimeter wave measurements;Skin;Temperature},
    doi={10.1109/TMTT.2002.803445},
    ISSN={0018-9480},
    month=oct,
    owner = {ofrey},
    
    }
    


  12. Jürgen Holzner and Richard Bamler. Burst-Mode and ScanSAR Interferometry. IEEE Transactions on Geoscience and Remote Sensing, 40(9):1917-1934, September 2002. Keyword(s): SAR Processing, Burst-mode, ScanSAR, Interferometry, pack-and-go algorithm, ENVISAT, RADARSAT, SRTM.
    Abstract: ScanSAR interferometry is an attractive option for efficient topographic mapping of large areas and for monitoring of large-scale motions. Only ScanSAR interferometry made it possible to map almost the entire landmass of the earth in the 11-day Shuttle Radar Topography Mission. Also the operational satellites RADARSAT and ENVISAT offer ScanSAR imaging modes and thus allow for repeat-pass ScanSAR interferometry. This paper gives a complete description of ScanSAR and burst-mode interferometric signal properties and compares different processing algorithms. The problems addressed are azimuth scanning pattern synchronization, spectral shift filtering in the presence of high squint, Doppler centroid estimation, different phase-preserving ScanSAR processing algorithms, ScanSAR interferogram formation, coregistration, and beam alignment. Interferograms and digital elevation models from RADARSAT ScanSAR Narrow modes are presented. The novel pack-and-go algorithm for efficient burst-mode range processing and a new time-variant fast interpolator for interferometric coregistration are introduced.

    @Article{HolzBaml:burstmode,
    Title = {{Burst-Mode and ScanSAR Interferometry}},
    Author = {J{\"u}rgen Holzner and Richard Bamler},
    Month = sep,
    Number = {9},
    Pages = {1917-1934},
    Volume = {40},
    Year = {2002},
    Abstract = {ScanSAR interferometry is an attractive option for efficient topographic mapping of large areas and for monitoring of large-scale motions. Only ScanSAR interferometry made it possible to map almost the entire landmass of the earth in the 11-day Shuttle Radar Topography Mission. Also the operational satellites RADARSAT and ENVISAT offer ScanSAR imaging modes and thus allow for repeat-pass ScanSAR interferometry. This paper gives a complete description of ScanSAR and burst-mode interferometric signal properties and compares different processing algorithms. The problems addressed are azimuth scanning pattern synchronization, spectral shift filtering in the presence of high squint, Doppler centroid estimation, different phase-preserving ScanSAR processing algorithms, ScanSAR interferogram formation, coregistration, and beam alignment. Interferograms and digital elevation models from RADARSAT ScanSAR Narrow modes are presented. The novel pack-and-go algorithm for efficient burst-mode range processing and a new time-variant fast interpolator for interferometric coregistration are introduced.},
    Journal = {IEEE Transactions on Geoscience and Remote Sensing},
    Keywords = {SAR Processing, Burst-mode, ScanSAR, Interferometry, pack-and-go algorithm, ENVISAT, RADARSAT, SRTM},
    Pdf = {../../../docs/holznerBamler02.pdf} 
    }
    


  13. Lance M. Kaplan, James H. McClellan, and Seung-Mok Oh. Prescreening During Image Formation for Ultrawideband Radar. IEEE Transactions on Aerospace and Electronic Systems, 38(1):74-88, January 2002. Keyword(s): SAR Processing, Back-Projection, Ultra-Wideband SAR, Prescreening, Quadtree Processing, Divide and Conquer Methods.
    Abstract: Standard radar image formation techniques waste computational resources by full resolving all areas of the scene, even regions of benign clutter. We introduce a multiscale prescreener algorithm that runs as part of the image formation processing step for ultrawideband (UWB) synthetic aperture radar (SAR) systems. The prescreener processes intermediate radar data generated by a quadtree backprojection image former. As the quadtree algorithm iterates, it is resolving increasingly finer subpatches of the scene. After each quadtree stage, the prescreener makes an estimate of the signal-to-background ratio of each subpatch and applies a constant false alarm rate (CFAR) detector to decide which ones might contain a target of interest. Whenever the prescreener determines that a subpatch is not near a detection, it cues the image former to terminate further processing of that subpatch. Using a small database of UWB radar field data, we demonstrate that the prescreener is able to decrease the overall computational load of the image formation process. We also show that the new multiscale prescreener method produces fewer false alarms than the conventional two-parameter CFAR prescreener applied to the completely formed image.

    @Article{KaplanEtAl02:Backproj,
    Title = {{Prescreening During Image Formation for Ultrawideband Radar}},
    Author = {Lance M. Kaplan and James H. McClellan and Seung-Mok Oh},
    Month = Jan,
    Number = {1},
    Pages = {74-88},
    Volume = {38},
    Year = {2002},
    Abstract = {Standard radar image formation techniques waste computational resources by full resolving all areas of the scene, even regions of benign clutter. We introduce a multiscale prescreener algorithm that runs as part of the image formation processing step for ultrawideband (UWB) synthetic aperture radar (SAR) systems. The prescreener processes intermediate radar data generated by a quadtree backprojection image former. As the quadtree algorithm iterates, it is resolving increasingly finer subpatches of the scene. After each quadtree stage, the prescreener makes an estimate of the signal-to-background ratio of each subpatch and applies a constant false alarm rate (CFAR) detector to decide which ones might contain a target of interest. Whenever the prescreener determines that a subpatch is not near a detection, it cues the image former to terminate further processing of that subpatch. Using a small database of UWB radar field data, we demonstrate that the prescreener is able to decrease the overall computational load of the image formation process. We also show that the new multiscale prescreener method produces fewer false alarms than the conventional two-parameter CFAR prescreener applied to the completely formed image.},
    Journal = {IEEE Transactions on Aerospace and Electronic Systems},
    Keywords = {SAR Processing, Back-Projection, Ultra-Wideband SAR, Prescreening, Quadtree Processing, Divide and Conquer Methods},
    Pdf = {../../../docs/kaplanEtAll02.pdf} 
    }
    


  14. Erik G. Larsson and Petre Stoica. Fast Implementation of Two-Dimensional APES and CAPON Spectral Estimators. Multidimensional Systems and Signal Processing, 13(1):35-53, 2002. Keyword(s): 2D Imaging, Capon, APES, Fast Implementation, Spectral Estimation, Beamforming.
    Abstract: The matched-filterbank spectral estimators APES and CAPON have recently received considerable attention in a number of applications. Unfortunately, their computational complexity tends to limit their usage in several cases --a problem that has previously been addressed by different authors. In this paper, we introduce a novel approach to the computation of the APES and CAPON spectra, which leads to a computational method that is considerably faster than all existing techniques. The new implementations of APES and CAPON are called fast APES and fast CAPON, respectively, and are developed for the two-dimensional case, with the one-dimensional case as a special case. Numerical examples are provided to demonstrate the application of APES to synthetic aperture radar (SAR) imaging, and to illustrate the reduction in computational complexity provided by our method.

    @Article{larssonStoica2002FastImplementationsOf2DAPESandCapon,
    author = {Larsson, Erik G. and Stoica, Petre},
    title = {Fast Implementation of Two-Dimensional {APES} and {CAPON} Spectral Estimators},
    journal = {Multidimensional Systems and Signal Processing},
    year = {2002},
    volume = {13},
    number = {1},
    pages = {35--53},
    abstract = {The matched-filterbank spectral estimators APES and CAPON have recently received considerable attention in a number of applications. Unfortunately, their computational complexity tends to limit their usage in several cases --a problem that has previously been addressed by different authors. In this paper, we introduce a novel approach to the computation of the APES and CAPON spectra, which leads to a computational method that is considerably faster than all existing techniques. The new implementations of APES and CAPON are called fast APES and fast CAPON, respectively, and are developed for the two-dimensional case, with the one-dimensional case as a special case. Numerical examples are provided to demonstrate the application of APES to synthetic aperture radar (SAR) imaging, and to illustrate the reduction in computational complexity provided by our method.},
    doi = {10.1023/A:1013891327453},
    file = {:larssonStoica2002FastImplementationsOf2DAPESandCapon.pdf:PDF},
    isbn = {1573-0824},
    keywords = {2D Imaging, Capon, APES, Fast Implementation, Spectral Estimation, Beamforming},
    owner = {ofrey},
    url = {https://doi.org/10.1023/A:1013891327453},
    
    }
    


  15. Christian Matzler. MATLAB functions for Mie scattering and absorption, version 2. IAP Res. Rep, 8:1-24, 2002.
    @Article{Maetzler2002,
    author = {Matzler, Christian},
    title = {MATLAB functions for Mie scattering and absorption, version 2},
    journal = {IAP Res. Rep},
    year = {2002},
    volume = {8},
    pages = {1--24},
    owner = {ofrey},
    
    }
    


  16. Christian Matzler. Relation between grain-size and correlation length of snow. Journal of Glaciology, 48(162):461-466, February 2002.
    Abstract: In the past it has often been difficult to compare results of different types of snow-structural information. Grain-size and correlation length are such parameters of granular media, and there exist different definitions and different measurement methods for both of them. The relation between these parameters is analyzed from theoretical and from experimental points of view, considering optical and microwave properties. For spherical ice grains the connecting formulas are simple, but for other shapes the two parameters are not directly related. Care must be taken in the measurement procedure. Especially if grain-size is regarded as the maximum extent of connected ice particles, the results are likely to lead to extreme overestimates. Therefore it is concluded that grain-size should be complemented by an additional size parameter, namely, the surface-to-volume ratio of equivalent spheres, i.e.a measure of the correlation length. Methods to determine this quantity in the laboratory have been known for a long time. Methods to obtain such measurements in the field are described here.

    @Article{matzlerJournalofGlaciology2002RelationGrainSizeCorrelationLength,
    author = {Christian Matzler},
    title = {Relation between grain-size and correlation length of snow},
    journal = {Journal of Glaciology},
    year = {2002},
    volume = {48},
    number = {162},
    pages = {461--466},
    month = {feb},
    abstract = {In the past it has often been difficult to compare results of different types of snow-structural information. Grain-size and correlation length are such parameters of granular media, and there exist different definitions and different measurement methods for both of them. The relation between these parameters is analyzed from theoretical and from experimental points of view, considering optical and microwave properties. For spherical ice grains the connecting formulas are simple, but for other shapes the two parameters are not directly related. Care must be taken in the measurement procedure. Especially if grain-size is regarded as the maximum extent of connected ice particles, the results are likely to lead to extreme overestimates. Therefore it is concluded that grain-size should be complemented by an additional size parameter, namely, the surface-to-volume ratio of equivalent spheres, i.e.a measure of the correlation length. Methods to determine this quantity in the laboratory have been known for a long time. Methods to obtain such measurements in the field are described here.},
    doi = {10.3189/172756502781831287},
    file = {:matzlerJournalofGlaciology2002RelationGrainSizeCorrelationLength.pdf:PDF},
    owner = {ofrey},
    publisher = {Cambridge University Press ({CUP})},
    
    }
    


  17. Jean-Luc Starck, E.J. Candes, and D.L. Donoho. The curvelet transform for image denoising. IEEE Transactions on Image Processing, 11(6):670-684, June 2002. Keyword(s): Cartesian samples, Fourier space, Fourier-domain, approximate digital Radon transform, approximate digital implementations, concentric squares geometry, curvelet coefficients, curvelet transform, decimated wavelet transforms, exact reconstruction, filter bank, frequency domain, image denoising, interpolation, low computational complexity, overcomplete wavelet pyramid, pseudo-polar sampling set, rectopolar grid, ridgelet transform, stability, tree-based Bayesian posterior mean methods, trous wavelet filters, undecimated wavelet transforms, visual performance, wavelet-based image reconstruction, white noise, Fourier transforms, Radon transforms, channel bank filters, filtering theory, image reconstruction, interpolation, wavelet transforms, white noise;.
    Abstract: We describe approximate digital implementations of two new mathematical transforms, namely, the ridgelet transform and the curvelet transform. Our implementations offer exact reconstruction, stability against perturbations, ease of implementation, and low computational complexity. A central tool is Fourier-domain computation of an approximate digital Radon transform. We introduce a very simple interpolation in the Fourier space which takes Cartesian samples and yields samples on a rectopolar grid, which is a pseudo-polar sampling set based on a concentric squares geometry. Despite the crudeness of our interpolation, the visual performance is surprisingly good. Our ridgelet transform applies to the Radon transform a special overcomplete wavelet pyramid whose wavelets have compact support in the frequency domain. Our curvelet transform uses our ridgelet transform as a component step, and implements curvelet subbands using a filter bank of a grave; trous wavelet filters. Our philosophy throughout is that transforms should be overcomplete, rather than critically sampled. We apply these digital transforms to the denoising of some standard images embedded in white noise. In the tests reported here, simple thresholding of the curvelet coefficients is very competitive with state of the art techniques based on wavelets, including thresholding of decimated or undecimated wavelet transforms and also including tree-based Bayesian posterior mean methods. Moreover, the curvelet reconstructions exhibit higher perceptual quality than wavelet-based reconstructions, offering visually sharper images and, in particular, higher quality recovery of edges and of faint linear and curvilinear features. Existing theory for curvelet and ridgelet transforms suggests that these new approaches can outperform wavelet methods in certain image reconstruction problems. The empirical results reported here are in encouraging agreement

    @Article{1014998,
    Title = {The curvelet transform for image denoising},
    Author = {Jean-Luc Starck and Candes, E.J. and Donoho, D.L.},
    Doi = {10.1109/TIP.2002.1014998},
    ISSN = {1057-7149},
    Month = jun,
    Number = {6},
    Pages = {670-684},
    Volume = {11},
    Year = {2002},
    Abstract = {We describe approximate digital implementations of two new mathematical transforms, namely, the ridgelet transform and the curvelet transform. Our implementations offer exact reconstruction, stability against perturbations, ease of implementation, and low computational complexity. A central tool is Fourier-domain computation of an approximate digital Radon transform. We introduce a very simple interpolation in the Fourier space which takes Cartesian samples and yields samples on a rectopolar grid, which is a pseudo-polar sampling set based on a concentric squares geometry. Despite the crudeness of our interpolation, the visual performance is surprisingly good. Our ridgelet transform applies to the Radon transform a special overcomplete wavelet pyramid whose wavelets have compact support in the frequency domain. Our curvelet transform uses our ridgelet transform as a component step, and implements curvelet subbands using a filter bank of a grave; trous wavelet filters. Our philosophy throughout is that transforms should be overcomplete, rather than critically sampled. We apply these digital transforms to the denoising of some standard images embedded in white noise. In the tests reported here, simple thresholding of the curvelet coefficients is very competitive with state of the art techniques based on wavelets, including thresholding of decimated or undecimated wavelet transforms and also including tree-based Bayesian posterior mean methods. Moreover, the curvelet reconstructions exhibit higher perceptual quality than wavelet-based reconstructions, offering visually sharper images and, in particular, higher quality recovery of edges and of faint linear and curvilinear features. Existing theory for curvelet and ridgelet transforms suggests that these new approaches can outperform wavelet methods in certain image reconstruction problems. The empirical results reported here are in encouraging agreement},
    Journal = {IEEE Transactions on Image Processing},
    Keywords = {Cartesian samples;Fourier space;Fourier-domain;approximate digital Radon transform;approximate digital implementations;concentric squares geometry;curvelet coefficients;curvelet transform;decimated wavelet transforms;exact reconstruction;filter bank;frequency domain;image denoising;interpolation;low computational complexity;overcomplete wavelet pyramid;pseudo-polar sampling set;rectopolar grid;ridgelet transform;stability;tree-based Bayesian posterior mean methods;trous wavelet filters;undecimated wavelet transforms;visual performance;wavelet-based image reconstruction;white noise;Fourier transforms;Radon transforms;channel bank filters;filtering theory;image reconstruction;interpolation;wavelet transforms;white noise;} 
    }
    


Conference articles

  1. P. Berardino, G. Fornaro, R. Lanari, E. Sansosti, F. Serafino, and F. Soldovieri. Multi-pass synthetic aperture radar for 3-D focusing. In Proc. IEEE Int. Geosci.Remote Sens. Symp., volume 1, pages 176-178, 2002. Keyword(s): SAR Processing, SAR Tomography, Tomography, geophysical techniques, radar imaging, radar theory, remote sensing by radar, synthetic aperture radar, terrain mapping, 3D focusing, SAR, SVD, geophysical measurement technique, land surface, multipass method, penetration depth, radar imaging, radar remote sensing, radar tomography, singular value decomposition, synthetic aperture radar, terrain mapping.
    Abstract: In the area of tomographic synthetic aperture radar processing wepresent a new technique that makes use of the singular value decomposition method to improve the resolution limits by including a-priori information about the radiation penetration depth.

    @InProceedings{bernardinoFornaroLanariSansostiSerafinoSoldovieri2002:Tomo,
    Title = {Multi-pass synthetic aperture radar for {3-D} focusing},
    Author = {Berardino, P. and Fornaro, G. and Lanari, R. and Sansosti, E. and Serafino, F. and Soldovieri, F.},
    Booktitle = {Proc. IEEE Int. Geosci.Remote Sens. Symp.},
    Pages = {176--178},
    Url = {http://ieeexplore.ieee.org/iel5/7969/22036/01024979.pdf},
    Volume = {1},
    Year = {2002},
    Abstract = {In the area of tomographic synthetic aperture radar processing wepresent a new technique that makes use of the singular value decomposition method to improve the resolution limits by including a-priori information about the radiation penetration depth.},
    Keywords = {SAR Processing, SAR Tomography, Tomography, geophysical techniques, radar imaging, radar theory, remote sensing by radar, synthetic aperture radar, terrain mapping, 3D focusing, SAR, SVD, geophysical measurement technique, land surface, multipass method, penetration depth, radar imaging, radar remote sensing, radar tomography, singular value decomposition, synthetic aperture radar, terrain mapping},
    Owner = {ofrey},
    Pdf = {../../../docs/berardinoFornaroLanariSnsostiSerafinoSoldovieriTomo02.pdf} 
    }
    


  2. P. Berens. Estimation of Carrier Track For High Precision SAR Imaging Using Active Reference Reflectors. In Proc. of EUSAR 2002 - 4th European Conference on Synthetic Aperture Radar, pages 241-244, 2002. Keyword(s): SAR Processing, Active Reflector, Transponder, Autofocus, Carrier Track Estimation, Flight Track Estimation, Kalman Filter, PAMIR, X-Band. DGPS, INS.
    Abstract: Synthetic aperture radar (SAR) processing needs precise information about the path of the radar sensor. Modern DGPS and INS systems are commonly used. However, for highest resolution, additional auto focus algorithms have to be implemented. The success of these algorithms depends strongly on the scene. For a reliable estimation of the flight path, a new idea is presented: active reference reflectors (transponders) within the scene receive the pulses of the radar system and reradiates them with an additional amplitude modulation. The echoes from these transponders can be separated from the echoes of the scene and offer an excellent basis for the estimation of the antenna track. The paper describes the processing steps to separate the echoes of the transponders from the scene echoes. The range histories from the antenna to the transponders can be determined very precisely afterwards. A Kalman filter combines the measured ranges and motion information given by a DGPS system to estimate the carrier track.

    @InProceedings{berensEUSAR2002:EstimFlightTrackPamir,
    Title = {Estimation of Carrier Track For High Precision SAR Imaging Using Active Reference Reflectors},
    Author = {P. Berens},
    Booktitle = {Proc. of EUSAR 2002 - 4th European Conference on Synthetic Aperture Radar},
    Pages = {241-244},
    Year = {2002},
    Abstract = {Synthetic aperture radar (SAR) processing needs precise information about the path of the radar sensor. Modern DGPS and INS systems are commonly used. However, for highest resolution, additional auto focus algorithms have to be implemented. The success of these algorithms depends strongly on the scene. For a reliable estimation of the flight path, a new idea is presented: active reference reflectors (transponders) within the scene receive the pulses of the radar system and reradiates them with an additional amplitude modulation. The echoes from these transponders can be separated from the echoes of the scene and offer an excellent basis for the estimation of the antenna track. The paper describes the processing steps to separate the echoes of the transponders from the scene echoes. The range histories from the antenna to the transponders can be determined very precisely afterwards. A Kalman filter combines the measured ranges and motion information given by a DGPS system to estimate the carrier track.},
    Keywords = {SAR Processing, Active Reflector, Transponder, Autofocus, Carrier Track Estimation, Flight Track Estimation, Kalman Filter, PAMIR, X-Band. DGPS, INS},
    Owner = {ofrey},
    Pdf = {../../../docs/berensEUSAR2002.pdf} 
    }
    


  3. Andreas R. Brenner. DISTRIBUTED SAR PROCESSING IN THE TIME DOMAIN. In Proc. of EUSAR 2002 - 4th European Conference on Synthetic Aperture Radar, 2002. Keyword(s): SAR Processing, Back-projection, Time-Domain Back-Projection, PAMIR, Distributed Processing, Parallel Processing.
    Abstract: The next generation airborne SAR sensors will comprise among others high resolution imaging capabilities (< 1 dm) and long range surveillance (> 100 km). This wide band and wide angle scenario requires an accurate modeling for SAR image formation with respect to motion compensation and focusing. This paper reports on the feasibility to jointly realise two approaches: First, a non-approximative time domain based SAR processor was developed. Second, because of its high computational burden, a distributed implementation on a heterogeneous workstation cluster by means of message passing interfaces was carried out. The evaluation of the processor on simulated data as well as an assessment of the distributed implementation is presented. The distributed time domain processor is successfully applied to data acquired with the new very wideband SAR sensor PAMIR of FGAN-FHR as well.

    @InProceedings{brennerEUSAR2002:TDBP,
    Title = {DISTRIBUTED SAR PROCESSING IN THE TIME DOMAIN},
    Author = {Andreas R. Brenner},
    Booktitle = {Proc. of EUSAR 2002 - 4th European Conference on Synthetic Aperture Radar},
    Year = {2002},
    Abstract = {The next generation airborne SAR sensors will comprise among others high resolution imaging capabilities (< 1 dm) and long range surveillance (> 100 km). This wide band and wide angle scenario requires an accurate modeling for SAR image formation with respect to motion compensation and focusing. This paper reports on the feasibility to jointly realise two approaches: First, a non-approximative time domain based SAR processor was developed. Second, because of its high computational burden, a distributed implementation on a heterogeneous workstation cluster by means of message passing interfaces was carried out. The evaluation of the processor on simulated data as well as an assessment of the distributed implementation is presented. The distributed time domain processor is successfully applied to data acquired with the new very wideband SAR sensor PAMIR of FGAN-FHR as well.},
    Keywords = {SAR Processing, Back-projection, Time-Domain Back-Projection,PAMIR, Distributed Processing, Parallel Processing},
    Owner = {ofrey},
    Pdf = {../../../docs/brennerEUSAR2002.pdf} 
    }
    


  4. Andreas R. Brenner and Joachim H. G. Ender. First Experimental Results Achieved With The New Very Wideband SAR System PAMIR. In Proc. of EUSAR 2002 - 4rd European Conference on Synthetic Aperture Radar, pages 81-86, 2002. Keyword(s): SAR Processing, Time-Domain Back-Projection, Back-Projection, PAMIR, Phased Array Multifunctional Imaging Radar, AER-II, X-Band, High Resolution, Wideband SAR.
    Abstract: Imaging radar systems in forthcoming surveillance and reconnaissance tasks have to meet increasingly severe demands. The next generation airborne SAR should comprise high resolution imaging capabilities (< 1 dm), long range surveillance (> 100 km), moving target indication (< 1 m/s) and a multitude of complex operational modes like MultipleSpotlight, ScanMTI and ISAR imaging of ground moving targets. At FGAN-FHR, where the experimental SAR system AER-II is successfully operational since 1996, a new experimental X-band system was conceived, which will possess in its final stage of realisation an electronically steerable phased array, five independent receive channels, a total signal bandwidth of about 1.8 GHz and will support novel multifunctional radar modes. The system is termed PAMIR (Phased Array Multifunctional Imaging Radar) and operates in its current realization with one channel and two horn antennas. In this paper, the first experimental results concerning calibration, synthetic bandwidth, motion compensation and high resolution image formation are presented.

    @InProceedings{brennerEnderEUSAR2002:PAMIR,
    Title = {First Experimental Results Achieved With The New Very Wideband SAR System PAMIR},
    Author = {Andreas R. Brenner and Joachim H. G. Ender},
    Booktitle = {Proc. of EUSAR 2002 - 4rd European Conference on Synthetic Aperture Radar},
    Pages = {81-86},
    Year = {2002},
    Abstract = {Imaging radar systems in forthcoming surveillance and reconnaissance tasks have to meet increasingly severe demands. The next generation airborne SAR should comprise high resolution imaging capabilities (< 1 dm), long range surveillance (> 100 km), moving target indication (< 1 m/s) and a multitude of complex operational modes like MultipleSpotlight, ScanMTI and ISAR imaging of ground moving targets. At FGAN-FHR, where the experimental SAR system AER-II is successfully operational since 1996, a new experimental X-band system was conceived, which will possess in its final stage of realisation an electronically steerable phased array, five independent receive channels, a total signal bandwidth of about 1.8 GHz and will support novel multifunctional radar modes. The system is termed PAMIR (Phased Array Multifunctional Imaging Radar) and operates in its current realization with one channel and two horn antennas. In this paper, the first experimental results concerning calibration, synthetic bandwidth, motion compensation and high resolution image formation are presented.},
    Keywords = {SAR Processing, Time-Domain Back-Projection, Back-Projection, PAMIR, Phased Array Multifunctional Imaging Radar, AER-II, X-Band, High Resolution, Wideband SAR},
    Owner = {ofrey},
    Pdf = {../../../docs/brennerEnderEUSAR2002.pdf} 
    }
    


  5. Yu Ding and David C. Munson, Jr.. A fast back-projection algorithm for bistatic SAR imaging. In Proc. Int. Conf. on Image Processing, volume 2, pages 449-452, 2002. Keyword(s): SAR Processing, Time-Domain Back-Projection, Back-projection, Bistatic SAR, image reconstruction, integral equations, radar imaging, synthetic aperture radar, tomography 2D interpolation, FFT, Fourier domain, Fourier domain data, bistatic SAR imaging, computational cost reduction, direct Fourier reconstruction, fast back-projection algorithm, image formation algorithms, integral equations, near-field imaging, nonCartesian grid, simulation results, synthetic aperture radar, tomography.
    Abstract: Using a far-field model, bistatic synthetic aperture radar (SAR) acquires Fourier data on a rather unusual, non-Cartesian grid in the Fourier domain. Previous image formation algorithms were mainly based on direct Fourier reconstruction to take advantage of the FFT, but the irregular coverage of the available Fourier domain data and the 2-D interpolation in the Fourier domain may adversely affect the accuracy of image reconstruction. Back-projection techniques avoid Fourier-domain interpolation, but ordinarily have huge computational cost. We present a fast back-projection algorithm for bistatic SAR imaging, motivated by a fast back-projection algorithm previously proposed for tomography. It has a reduced computational cost, on the same order as that of direct Fourier reconstruction. Furthermore, this approach can be used for near-field imaging. Simulation results verify the performance of this new algorithm.

    @InProceedings{dingMunson2002:BistaticFastBackp,
    author = {Yu Ding and David C. {Munson, Jr.}},
    booktitle = {Proc. Int. Conf. on Image Processing},
    title = {A fast back-projection algorithm for bistatic {SAR} imaging},
    year = {2002},
    pages = {449--452},
    volume = {2},
    abstract = {Using a far-field model, bistatic synthetic aperture radar (SAR) acquires Fourier data on a rather unusual, non-Cartesian grid in the Fourier domain. Previous image formation algorithms were mainly based on direct Fourier reconstruction to take advantage of the FFT, but the irregular coverage of the available Fourier domain data and the 2-D interpolation in the Fourier domain may adversely affect the accuracy of image reconstruction. Back-projection techniques avoid Fourier-domain interpolation, but ordinarily have huge computational cost. We present a fast back-projection algorithm for bistatic SAR imaging, motivated by a fast back-projection algorithm previously proposed for tomography. It has a reduced computational cost, on the same order as that of direct Fourier reconstruction. Furthermore, this approach can be used for near-field imaging. Simulation results verify the performance of this new algorithm.},
    doi = {10.1109/ICIP.2002.1039984},
    issn = {1522-4880},
    keywords = {SAR Processing, Time-Domain Back-Projection, Back-projection, Bistatic SAR, image reconstruction, integral equations, radar imaging, synthetic aperture radar, tomography 2D interpolation, FFT, Fourier domain, Fourier domain data, bistatic SAR imaging, computational cost reduction, direct Fourier reconstruction, fast back-projection algorithm, image formation algorithms, integral equations, near-field imaging, nonCartesian grid, simulation results, synthetic aperture radar, tomography},
    owner = {ofrey},
    
    }
    


  6. Armin W. Doerry, Fred M. Dickey, Louis A. Romero, and John M. DeLaurentis. Difficulties in Superresolving Synthetic Aperture Radar Images. In Edmund G. Zelnio, editor, Proc. of SPIE Vol. 4727, Algorithms for Synthetic Aperture Radar Imagery IX, number 1, pages 122-133, 2002. SPIE. Keyword(s): SAR Processing, Superresolution, Super Resolution, High Resolution, Fine Resolution, Spectral Estimation.
    Abstract: The ability to resolve Synthetic Aperture Radar (SAR) images to finer resolutions than the system bandwidths classically allow is a tantalizing prospect. Seemingly superresolution offers something for nothing, or at least something better than the system was designed for if only we process enough or right. Over the years this has proved to be a rather popular area of investigation, generating a wide variety of algorithms and corresponding claims of performance. Nevertheless, the literature on the fundamental underlying principles of superresolution as applied to SAR has been rather anemic. This paper addresses the following questions: What exactly is superresolution? and What is not really superresolution, but perhaps more aptly described as image enhancement? Is true superresolution possible? and to what degree? What constrains superresolution? and very importantly, How should we objectively test whether an image is in fact superresolved? Whereas superresolution concepts offer the potential of resolution beyond the classical limit, this great promise has not generally been realized. That is not to say that many reported algorithms have no useful effect on images. True superresolution is defined herein as the recovery of true scene spectrum, that allows more accurate scene rendering. The analytical basis for superresolution theory is outlined, and the application to SAR is then investigated as an operator inversion problem, which is generally ill posed. Noise inherent in radar data tends to severely inhibit significant enhancement of image resolution. A criterion for judging superresolution processing of an image is presented.

    @InProceedings{DoerryDickeyRomeroDeLaurentis2002,
    author = {Armin W. Doerry and Fred M. Dickey and Louis A. Romero and John M. DeLaurentis},
    title = {Difficulties in Superresolving Synthetic Aperture Radar Images},
    booktitle = {Proc. of SPIE Vol. 4727, Algorithms for Synthetic Aperture Radar Imagery IX},
    year = {2002},
    editor = {Edmund G. Zelnio},
    number = {1},
    pages = {122-133},
    publisher = {SPIE},
    abstract = {The ability to resolve Synthetic Aperture Radar (SAR) images to finer resolutions than the system bandwidths classically allow is a tantalizing prospect. Seemingly superresolution offers something for nothing, or at least something better than the system was designed for if only we process enough or right. Over the years this has proved to be a rather popular area of investigation, generating a wide variety of algorithms and corresponding claims of performance. Nevertheless, the literature on the fundamental underlying principles of superresolution as applied to SAR has been rather anemic. This paper addresses the following questions: What exactly is superresolution? and What is not really superresolution, but perhaps more aptly described as image enhancement? Is true superresolution possible? and to what degree? What constrains superresolution? and very importantly, How should we objectively test whether an image is in fact superresolved? Whereas superresolution concepts offer the potential of resolution beyond the classical limit, this great promise has not generally been realized. That is not to say that many reported algorithms have no useful effect on images. True superresolution is defined herein as the recovery of true scene spectrum, that allows more accurate scene rendering. The analytical basis for superresolution theory is outlined, and the application to SAR is then investigated as an operator inversion problem, which is generally ill posed. Noise inherent in radar data tends to severely inhibit significant enhancement of image resolution. A criterion for judging superresolution processing of an image is presented.},
    file = {:DoerryDickeyRomeroDeLaurentis2002.pdf:PDF},
    keywords = {SAR Processing, Superresolution, Super Resolution, High Resolution, Fine Resolution, Spectral Estimation},
    location = {Orlando, FL, USA},
    owner = {ofrey},
    pdf = {../../../docs/DoerryDickeyRomeroDeLaurentis2002.pdf},
    url = {http://link.aip.org/link/?PSI/4727/122/1},
    
    }
    


  7. P. Dubois-Fernandez, O. R. du Plessis, D. le Coz, J. Dupas, B. Vaizan, X. Dupuis, H. Cantalloube, C. Coulombeix, C. Titin-Schnaider, P. Dreuillet, J. M. Boutry, J. P. Canny, L. Kaisersmertz, J. Peyret, P. Martineau, M. Chanteclerc, L. Pastore, and J. P. Bruyant. The ONERA RAMSES SAR system. In IEEE International Geoscience and Remote Sensing Symposium, volume 3, pages 1723-1725 vol.3, June 2002. Keyword(s): SAR Processing, W-Band, airborne radar, geophysical signal processing, geophysical techniques, radar polarimetry, remote sensing by radar, synthetic aperture radar, terrain mapping, 0.43 to 95 GHz, C-band, EHF, InSAR, K-band, Ka-band, Ku-band, L-band, ONERA, P-band, RAMSES, S-band, SAR, SHF, TDRI, UHF, W-band, X-band, airborne radar, algorithm, geophysical measurement technique, instrument, land surface, radar polarimetry, radar remote sensing, synthetic aperture radar, target detection recognition and identification, terrain mapping, Calibration, Frequency, Interferometry, Object detection, Radar applications, Radar imaging, Space technology, Synthetic aperture radar, System testing, Target recognition.
    Abstract: The ONERA RAMSES system (Radar Aeroporte Multi-spectral d'Etude des Signatures) is a flexible SAR system in constant evolution developed mainly as a test bench for new technologies and to provide specific data for TDRI (Target Detection, Recognition and Identification) algorithm evaluation. It is flown on a Transall C160 platform operated by the CEV (Centre d'Essais en Vol). This paper gives an overview of the system and its recent upgradings.

    @INPROCEEDINGS{DuboisFernandezEtAlIGARSS2002OneraRAMSESSARWBAND,
    author={P. Dubois-Fernandez and O. R. du Plessis and D. le Coz and J. Dupas and B. Vaizan and X. Dupuis and H. Cantalloube and C. Coulombeix and C. Titin-Schnaider and P. Dreuillet and J. M. Boutry and J. P. Canny and L. Kaisersmertz and J. Peyret and P. Martineau and M. Chanteclerc and L. Pastore and J. P. Bruyant},
    booktitle={IEEE International Geoscience and Remote Sensing Symposium},
    title={The ONERA RAMSES SAR system},
    year={2002},
    volume={3},
    number={},
    pages={1723-1725 vol.3},
    abstract={The ONERA RAMSES system (Radar Aeroporte Multi-spectral d'Etude des Signatures) is a flexible SAR system in constant evolution developed mainly as a test bench for new technologies and to provide specific data for TDRI (Target Detection, Recognition and Identification) algorithm evaluation. It is flown on a Transall C160 platform operated by the CEV (Centre d'Essais en Vol). This paper gives an overview of the system and its recent upgradings.},
    keywords={SAR Processing, W-Band,airborne radar;geophysical signal processing;geophysical techniques;radar polarimetry;remote sensing by radar;synthetic aperture radar;terrain mapping;0.43 to 95 GHz;C-band;EHF;InSAR;K-band;Ka-band;Ku-band;L-band;ONERA;P-band;RAMSES;S-band;SAR;SHF;TDRI;UHF;W-band;X-band;airborne radar;algorithm;geophysical measurement technique;instrument;land surface;radar polarimetry;radar remote sensing;synthetic aperture radar;target detection recognition and identification;terrain mapping;Calibration;Frequency;Interferometry;Object detection;Radar applications;Radar imaging;Space technology;Synthetic aperture radar;System testing;Target recognition},
    doi={10.1109/IGARSS.2002.1026233},
    ISSN={},
    month=jun,
    owner = {ofrey},
    
    }
    


  8. Joachim H.G. Ender and Andreas R. Brenner. PAMIR - A Wideband Phased Array SAR/MTI System. In Proc. of EUSAR 2002 - 4th European Conference on Synthetic Aperture Radar, pages 157-162, 2002. Keyword(s): SAR Processing, PAMIR, MTI, GMTI, Time-Domain Back-Projection, Back-Projection, Spotlight SAR, FGAN, X-Band, InSAR 1.8 GHz, ISAR, IfSAR, Phased Array Multifunctional Imaging Radar, X-band radar, airborne imaging radar, electronically steerable phased array, ground moving objects, ground moving target indication, ground-moving target indication, inverse SAR, long-range imaging capabilities, multichannel capability, operational modes, receive channels, reconfigurable phased array antenna, reconnaissance tasks, resolution, signal bandwidth, single-pass interferometric SAR, space-time adaptive processing, spaceborne imaging radar, subapertures, surveillance, synthetic aperture radar, wideband phased array SAR/MTI system, wideband system design.
    Abstract: Future air- and spacebased reconnaissance systems will be equipped with long range radar platforms of high flexibility, very high resolution in the order of one decimetre, covering a large angular sector and operating in sophisticated modes using multi channel signal processing. This variety of tasks can be fulfilled only by use of a phased array antenna. The need for a large bandwidth rises a lot of problems to be solved. To study the achievable performance in practice, FGAN-FHR has decided to build up an experimental system: PAMIR, the Phased Array Multifunctional Imaging Radar. Now, the system has come to a first stage allowing to gather preliminary radar data using a simple horn antenna. The phased array antenna is planned to be available in 2003.

    @InProceedings{enderBrennerEUSAR2002:PAMIR,
    Title = {PAMIR - A Wideband Phased Array SAR/MTI System},
    Author = {Joachim H.G. Ender and Andreas R. Brenner},
    Booktitle = {Proc. of EUSAR 2002 - 4th European Conference on Synthetic Aperture Radar},
    Pages = {157-162},
    Year = {2002},
    Abstract = {Future air- and spacebased reconnaissance systems will be equipped with long range radar platforms of high flexibility, very high resolution in the order of one decimetre, covering a large angular sector and operating in sophisticated modes using multi channel signal processing. This variety of tasks can be fulfilled only by use of a phased array antenna. The need for a large bandwidth rises a lot of problems to be solved. To study the achievable performance in practice, FGAN-FHR has decided to build up an experimental system: PAMIR, the Phased Array Multifunctional Imaging Radar. Now, the system has come to a first stage allowing to gather preliminary radar data using a simple horn antenna. The phased array antenna is planned to be available in 2003.},
    Keywords = {SAR Processing, PAMIR, MTI, GMTI, Time-Domain Back-Projection, Back-Projection, Spotlight SAR, FGAN, X-Band, InSAR 1.8 GHz, ISAR, IfSAR, Phased Array Multifunctional Imaging Radar, X-band radar, airborne imaging radar, electronically steerable phased array, ground moving objects, ground moving target indication, ground-moving target indication, inverse SAR, long-range imaging capabilities, multichannel capability, operational modes, receive channels, reconfigurable phased array antenna, reconnaissance tasks, resolution, signal bandwidth, single-pass interferometric SAR, space-time adaptive processing, spaceborne imaging radar, subapertures, surveillance, synthetic aperture radar, wideband phased array SAR/MTI system, wideband system design},
    Owner = {ofrey},
    Pdf = {../../../docs/enderBrennerEUSAR2002.pdf} 
    }
    


  9. Irena Hajnsek, Konstantinos P. Papathanassiou, Alberto Moreira, and Shane R. Cloude. Surface parameter estimation using interferometric and polarimetric SAR. In Proc. IEEE Int. Geoscience and Remote Sensing Symp, volume 1, pages 420-422 vol.1, 2002. Keyword(s): backscatter, geophysical techniques, hydrological techniques, radar cross-sections, radar polarimetry, radar theory, remote sensing by radar, synthetic aperture radar, terrain mapping, backscatter, geophysical measurement technique, hydrology, interferometric SAR, interferometric coherence, land surface, moisture, polarimetric SAR, radar polarimetry, radar remote sensing, radar scattering, soil moisture, surface parameter estimation, surface roughness, surface scattering model, synthetic aperture radar, terrain mapping, Anisotropic magnetoresistance, Coherence, Decorrelation, Parameter estimation, Polarization, Reflectivity, Rough surfaces, Scattering, Surface roughness, Surface topography.
    @InProceedings{Hajnsek2002,
    author = {Irena Hajnsek and Konstantinos P. Papathanassiou and Alberto Moreira and Shane R. Cloude},
    title = {Surface parameter estimation using interferometric and polarimetric {SAR}},
    booktitle = {Proc. IEEE Int. Geoscience and Remote Sensing Symp},
    year = {2002},
    volume = {1},
    pages = {420--422 vol.1},
    doi = {10.1109/IGARSS.2002.1025059},
    keywords = {backscatter, geophysical techniques, hydrological techniques, radar cross-sections, radar polarimetry, radar theory, remote sensing by radar, synthetic aperture radar, terrain mapping, backscatter, geophysical measurement technique, hydrology, interferometric SAR, interferometric coherence, land surface, moisture, polarimetric SAR, radar polarimetry, radar remote sensing, radar scattering, soil moisture, surface parameter estimation, surface roughness, surface scattering model, synthetic aperture radar, terrain mapping, Anisotropic magnetoresistance, Coherence, Decorrelation, Parameter estimation, Polarization, Reflectivity, Rough surfaces, Scattering, Surface roughness, Surface topography},
    owner = {ofrey},
    
    }
    


  10. Andrea Monti-Guarnieri. Processing Strategies for Phase Unwrapping for InSAR Applications. In Proc. of EUSAR 2002 - 4th European Conference on Synthetic Aperture Radar, volume 1, Ulm, Germany, pages 349-352, May 2002. Keyword(s): SAR Processing, Interferometry, Phase Unwrapping, Multifractal Modelling of Earth Topography.
    Abstract: We exploit the terrain statistics derived from multifractal modelling of earth topography to derive some statistical properties of SAR interferogram, with particular reference to the gradient of the unwrapped phase.

    @InProceedings{monti02:phaseUnWrap,
    Title = {{Processing Strategies for Phase Unwrapping for InSAR Applications}},
    Author = {Andrea Monti-Guarnieri},
    Booktitle = {Proc. of EUSAR 2002 - 4th European Conference on Synthetic Aperture Radar},
    Month = may,
    Pages = {349-352},
    Volume = {1},
    Year = {2002},
    Abstract = {We exploit the terrain statistics derived from multifractal modelling of earth topography to derive some statistical properties of SAR interferogram, with particular reference to the gradient of the unwrapped phase.},
    Address = {Ulm, Germany},
    Keywords = {SAR Processing, Interferometry, Phase Unwrapping, Multifractal Modelling of Earth Topography},
    Pdf = {../../../docs/monti02.pdf} 
    }
    


  11. R.L. Morrison, Jr. and David C. Munson, Jr.. An experimental study of a new entropy-based SAR autofocus technique. In Image Processing. 2002. Proceedings. 2002 International Conference on, volume 2, pages 441-444, September 2002. Keyword(s): SAR Processing, Autofocus, Phase Gradient Autofocus.
    @InProceedings{Morrison2002,
    Title = {An experimental study of a new entropy-based SAR autofocus technique},
    Author = {{Morrison, Jr.}, R.L. and {Munson, Jr.}, David C.},
    Booktitle = {Image Processing. 2002. Proceedings. 2002 International Conference on},
    Doi = {10.1109/ICIP.2002.1039982},
    Month = sep,
    Pages = {441--444},
    Volume = {2},
    Year = {2002},
    Keywords = {SAR Processing, Autofocus, Phase Gradient Autofocus},
    Owner = {ofrey} 
    }
    


  12. Clifford J. Nolan and Margaret Cheney. Synthetic Aperture Inversion For Non-Flat Topography. In Proc. of EUSAR 2002 - 4th European Conference on Synthetic Aperture Radar, volume 1, pages 105-108, 2002. Keyword(s): SAR Processing, Back-Projection, Non-Flat Topography, Time-Domain Back-Projection, TDBP.
    Abstract: This paper considers Synthetic Aperture Radar and other synthetic aperture imaging systems in which a backscattered wave is measured from positions along a single flight track. We assume that the ground topography is known but not necessarily flat. We consider two cases, corresponding to the degree of directionality of the antenna. For the high-directivity case, we propose an imaging algorithm involving backprojection and a spatially varying filter that corrects for the antenna beam pattern, source waveform, and other geometrical factors. We give conditions on the relationship between the flight track and the topography to avoid artifacts. We show that the algorithm correctly reproduces certain features of the scene. For the case of an antenna with poor directionality, the image produced by the above algorithm contains artifacts. For this case, we analyze the strength of the artifacts relative to the strength of the true image. The analysis of this paper shows that the artifacts can be somewhat suppressed by increasing the curvature of the flight track and by keeping the desired target in view for as long as possible.

    @InProceedings{nolancheney:SARInversion,
    Title = {{Synthetic Aperture Inversion For Non-Flat Topography}},
    Author = {Clifford J. Nolan and Margaret Cheney},
    Booktitle = {Proc. of EUSAR 2002 - 4th European Conference on Synthetic Aperture Radar},
    Pages = {105-108},
    Url = {www.rpi.edu/~cheney/papers/eusar.pdf},
    Volume = {1},
    Year = {2002},
    Abstract = {This paper considers Synthetic Aperture Radar and other synthetic aperture imaging systems in which a backscattered wave is measured from positions along a single flight track. We assume that the ground topography is known but not necessarily flat. We consider two cases, corresponding to the degree of directionality of the antenna. For the high-directivity case, we propose an imaging algorithm involving backprojection and a spatially varying filter that corrects for the antenna beam pattern, source waveform, and other geometrical factors. We give conditions on the relationship between the flight track and the topography to avoid artifacts. We show that the algorithm correctly reproduces certain features of the scene. For the case of an antenna with poor directionality, the image produced by the above algorithm contains artifacts. For this case, we analyze the strength of the artifacts relative to the strength of the true image. The analysis of this paper shows that the artifacts can be somewhat suppressed by increasing the curvature of the flight track and by keeping the desired target in view for as long as possible.},
    Keywords = {SAR Processing, Back-Projection, Non-Flat Topography, Time-Domain Back-Projection, TDBP},
    Pdf = {../../../docs/nolan02.pdf} 
    }
    


  13. Mats I. Pettersson. Detection of Moving Target in Wideband SAR Using Fast Time Backprojection Processing. In Proc. of EUSAR 2002 - 4th European Conference on Synthetic Aperture Radar, volume 1, pages 217-220, 2002. Keyword(s): SAR Processing, Back-Projection, Fast Back-Projection, TDBP, Time-Domain Back-Projection, Moving Target Indication, Ultra-Wideband SAR.
    Abstract: A likelihood ratio test is proposed for moving target detection in an ultra wide frequency band and wide antenna beam (wide band) SAR system. The developed method combines time domain fast backprojection SAR processing methods with moving target detection. It saves computational load when all relative speeds can be tested using the same clutter suppressed sub-aperture beams. The proposed method is tested on narrow band radar data.

    @InProceedings{pettersson:backproj,
    Title = {{Detection of Moving Target in Wideband SAR Using Fast Time Backprojection Processing}},
    Author = {Mats I. Pettersson},
    Booktitle = {Proc. of EUSAR 2002 - 4th European Conference on Synthetic Aperture Radar},
    Pages = {217-220},
    Url = {http://www.fhr.fgan.de/eusar/Conf__Program/Second_Day/second_day.html},
    Volume = {1},
    Year = {2002},
    Abstract = {A likelihood ratio test is proposed for moving target detection in an ultra wide frequency band and wide antenna beam (wide band) SAR system. The developed method combines time domain fast backprojection SAR processing methods with moving target detection. It saves computational load when all relative speeds can be tested using the same clutter suppressed sub-aperture beams. The proposed method is tested on narrow band radar data.},
    Keywords = {SAR Processing, Back-Projection, Fast Back-Projection, TDBP, Time-Domain Back-Projection, Moving Target Indication, Ultra-Wideband SAR},
    Pdf = {../../../docs/pettersson02.pdf} 
    }
    


  14. Athanasios Potsis, Andreas Reigber, Emmanouil Alivizatos, Alberto Moreira, and Nikolaos K. Uzunoglou. Comparison of Chirp Scaling and Wavenumber Domain Algorithms for Airborne Low-Frequency SAR. In Francesco Posa, editor, SAR Image Analysis, Modeling, and Techniques V, volume 4883, pages 25-36, March 2002. Keyword(s): SAR Processing, Chirp Scaling Algorithm, Extended Chirp Scaling Algorithm, omega-k, Range Migration Algorithm, Wavenumber Domain Algorithm, Comparison of Algorithms, P-Band, Wideband SAR, Airborne SAR.
    Abstract: In recent years a new class of Synthetic Aperture Radar (SAR) systems, using low frequencies, have emerged. The combination of low frequencies with high bandwidths allows a variety of new applications. Several new fields arise in forestry, biomass estimation and in archaeological and geological exploration. The P-band SAR technology benefits from technological advances in antenna design, low noise amplifiers, band pass filters, digital receiver technology, as well as new processing algorithms. For all the new applications of an airborne P-band SAR system, the high-resolution imaging is an important parameter, but it cannot be easily achieved with conventional processing techniques. In this paper, the performance and limitations of the Extended Chirp Scaling (ECS) algorithm and wavenumber domain Omega-K processing algorithm are analysed and discussed. Additionally, modifications of both algorithms are proposed, which optimise the respective algorithm for processing low frequency, wide-beam and wide-band SAR data. Despite of the inherent limitations of the above mentioned processing algorithms, a deterministic phase error, called ``digital phase error'', due to digital signal processing characteristics is formulated and its effect to the processed SAR data is analytically described. The analysis is carried out, using simulated low frequency airborne SAR data.

    @InProceedings{PotsisReigAliMorUzun02:Comparison,
    Title = {{Comparison of Chirp Scaling and Wavenumber Domain Algorithms for Airborne Low-Frequency SAR}},
    Author = {Athanasios Potsis and Andreas Reigber and Emmanouil Alivizatos and Alberto Moreira and Nikolaos K. Uzunoglou},
    Booktitle = {SAR Image Analysis, Modeling, and Techniques V},
    Editor = {Francesco Posa},
    Month = mar,
    Pages = {25-36},
    Url = {http://www.cv.tu-berlin.de/publications/pdf/potsis02_processing2.pdf},
    Volume = {4883},
    Year = {2002},
    Abstract = {In recent years a new class of Synthetic Aperture Radar (SAR) systems, using low frequencies, have emerged. The combination of low frequencies with high bandwidths allows a variety of new applications. Several new fields arise in forestry, biomass estimation and in archaeological and geological exploration. The P-band SAR technology benefits from technological advances in antenna design, low noise amplifiers, band pass filters, digital receiver technology, as well as new processing algorithms. For all the new applications of an airborne P-band SAR system, the high-resolution imaging is an important parameter, but it cannot be easily achieved with conventional processing techniques. In this paper, the performance and limitations of the Extended Chirp Scaling (ECS) algorithm and wavenumber domain Omega-K processing algorithm are analysed and discussed. Additionally, modifications of both algorithms are proposed, which optimise the respective algorithm for processing low frequency, wide-beam and wide-band SAR data. Despite of the inherent limitations of the above mentioned processing algorithms, a deterministic phase error, called ``digital phase error'', due to digital signal processing characteristics is formulated and its effect to the processed SAR data is analytically described. The analysis is carried out, using simulated low frequency airborne SAR data.},
    Keywords = {SAR Processing, Chirp Scaling Algorithm, Extended Chirp Scaling Algorithm, omega-k, Range Migration Algorithm, Wavenumber Domain Algorithm, Comparison of Algorithms, P-Band, Wideband SAR, Airborne SAR},
    Pdf = {../../../docs/PotsisReigAliMorUzun02.pdf} 
    }
    


  15. Rolf Scheiber and V. M. Bothale. Application of Multi-Look Techniques for Interferometric SAR Data. In Proc. of EUSAR 2002 - 4th European Conference on Synthetic Aperture Radar, Cologne, Germany, pages 77-80, June 2002. Keyword(s): SAR Processing, Extended Chirp Scaling, ECS, Chirp Scaling, CS, Azimuth Focusing, Multi-Look Processing, Non-Linear Flight Paths, Non-Linear SAR, Interferometry, InSAR, E-SAR, Airborne SAR, SAR interferometry, azimuth registration, geophysical measurement technique, image registration, interferometric SAR, land surface, motion compensation, multi-look method, multi-pass airborne method, multilook method, radar remote sensing, residual motion errors, spectral domain multi-look approach, synthetic aperture radar, terrain mapping.
    Abstract: Two different multi-look techniques for interferometric SAR data are investigated in the first part of this paper. The first one uses the box-car type of filter on the complex interferogram in the spatial domain, whereas the second one performs look-wise filtering of the individual images in the spectral domain with subsequent coherent addition of the look-wise interferograms. Next, it is shown that the flexibility of the spectral domain multi-look technique can be used for improved motion compensation and further for precisely updated estimation of azimuth misregistration offsets. This leads finally to the compensation of residual motion errors in case of multi-pass SAR interferometry. Investigations using data of the DLR owned airborne ESAR system are presented.

    @InProceedings{scheiberBothale2002:multiLookProcessing,
    Title = {{Application of Multi-Look Techniques for Interferometric SAR Data}},
    Author = {Rolf Scheiber and V. M. Bothale},
    Booktitle = {Proc. of EUSAR 2002 - 4th European Conference on Synthetic Aperture Radar},
    Month = {jun},
    Pages = {77-80},
    Year = {2002},
    Abstract = {Two different multi-look techniques for interferometric SAR data are investigated in the first part of this paper. The first one uses the box-car type of filter on the complex interferogram in the spatial domain, whereas the second one performs look-wise filtering of the individual images in the spectral domain with subsequent coherent addition of the look-wise interferograms. Next, it is shown that the flexibility of the spectral domain multi-look technique can be used for improved motion compensation and further for precisely updated estimation of azimuth misregistration offsets. This leads finally to the compensation of residual motion errors in case of multi-pass SAR interferometry. Investigations using data of the DLR owned airborne ESAR system are presented.},
    Address = {Cologne, Germany},
    Keywords = {SAR Processing, Extended Chirp Scaling, ECS, Chirp Scaling, CS, Azimuth Focusing, Multi-Look Processing, Non-Linear Flight Paths, Non-Linear SAR, Interferometry, InSAR, E-SAR, Airborne SAR, SAR interferometry, azimuth registration, geophysical measurement technique, image registration, interferometric SAR, land surface, motion compensation, multi-look method, multi-pass airborne method, multilook method, radar remote sensing, residual motion errors, spectral domain multi-look approach, synthetic aperture radar, terrain mapping},
    Owner = {ofrey},
    Pdf = {../../../docs/scheiberBothaleEusar2002.pdf} 
    }
    


  16. Rolf Scheiber and V.M. Bothale. Interferometric multi-look techniques for SAR data. In IEEE International Geoscience and Remote Sensing Symposium, IGARSS '02, volume 1, pages 173-175, 2002. Keyword(s): SAR Processing, Extended Chirp Scaling, ECS, Chirp Scaling, CS, Azimuth Focusing, Multi-Look Processing, Non-Linear Flight Paths, Non-Linear SAR, Interferometry, InSAR, E-SAR, Airborne SAR, airborne radar, geophysical signal processing, geophysical techniques, radar imaging, remote sensing by radar, synthetic aperture radar, terrain mapping, SAR interferometry, azimuth registration, geophysical measurement technique, image registration, interferometric SAR, land surface, motion compensation, multi-look method, multi-pass airborne method, multilook method, radar remote sensing, residual motion errors, spectral domain multi-look approach, synthetic aperture radar, terrain mapping.
    Abstract: This paper addresses the benefits of the spectral domain multi-look approach for SAR interferometry. A comparison with the wide spread spatial averaging filter is included in the beginning. Next, it is shown that the flexibility of the spectral domain multi-look technique can be used for improved motion compensation and further for precisely updated estimation of azimuth misregistration offsets. This leads finally to the compensation of residual motion errors in case of multi-pass airborne SAR interferometry, e.g. for the E-SAR system of DLR.

    @InProceedings{scheiberBothaleIgarss2002:multiLookProcessing,
    author = {Scheiber, Rolf and Bothale, V.M.},
    booktitle = {IEEE International Geoscience and Remote Sensing Symposium, IGARSS '02},
    title = {Interferometric multi-look techniques for SAR data},
    year = {2002},
    pages = {173--175},
    volume = {1},
    abstract = {This paper addresses the benefits of the spectral domain multi-look approach for SAR interferometry. A comparison with the wide spread spatial averaging filter is included in the beginning. Next, it is shown that the flexibility of the spectral domain multi-look technique can be used for improved motion compensation and further for precisely updated estimation of azimuth misregistration offsets. This leads finally to the compensation of residual motion errors in case of multi-pass airborne SAR interferometry, e.g. for the E-SAR system of DLR.},
    keywords = {SAR Processing, Extended Chirp Scaling, ECS, Chirp Scaling, CS, Azimuth Focusing, Multi-Look Processing, Non-Linear Flight Paths, Non-Linear SAR, Interferometry, InSAR, E-SAR, Airborne SAR, airborne radar, geophysical signal processing, geophysical techniques, radar imaging, remote sensing by radar, synthetic aperture radar, terrain mapping, SAR interferometry, azimuth registration, geophysical measurement technique, image registration, interferometric SAR, land surface, motion compensation, multi-look method, multi-pass airborne method, multilook method, radar remote sensing, residual motion errors, spectral domain multi-look approach, synthetic aperture radar, terrain mapping},
    owner = {ofrey},
    pdf = {../../../docs/scheiberBothaleIgarss2002.pdf},
    url = {http://ieeexplore.ieee.org/iel5/7969/22036/01024978.pdf},
    
    }
    


  17. H. Schimpf, H. Essen, S. Boehmsdorff, and T. Brehm. MEMPHIS-a fully polarimetric experimental radar. In Proc. IEEE Int. Geosci. Remote Sens. Symp., volume 3, pages 1714-1716, June 2002. Keyword(s): SAR Processing, W-Band, MEMPHIS, Airborne SAR, UAV, Fraunhofer, calibration, geophysical equipment, geophysical techniques, radar polarimetry, remote sensing by radar, synthetic aperture radar, terrain mapping, 5 to 36 GHz, 75 to 110 GHz, EHF, InSAR, Ka-band, MEMPHIS, SHF, W-band, X-band, across-track interferometry, calibration, forward squinted Doppler beam sharpening mode, geophysical measurement technique, land surface, polarimetric SAR, radar polarimetry, radar remote sensing, side-looking mode, synthetic aperture radar, technical description, terrain mapping, Calibration, Chirp, Frequency, Polarization, Radar antennas, Radar polarimetry, Receiving antennas, Satellite broadcasting, Synthetic aperture radar, Transmitting antennas.
    Abstract: The MEMPHIS polarimetric SAR is able to operate simultaneously at X-, Ka- and W-band. After a detailed technical description, several examples are given to demonstrate its capabilities in the side-looking mode, in forward squinted Doppler beam sharpenung (DBS) mode and with across-track interferometry. Of great importance is the polarimetric calibration which is described in some detail.

    @INPROCEEDINGS{schimpfEssenBoehmsdorffBrehmIGARSS2002MemphisWBandKaBandSAR,
    author={H. Schimpf and H. Essen and S. Boehmsdorff and T. Brehm},
    booktitle={Proc. IEEE Int. Geosci. Remote Sens. Symp.},
    title={MEMPHIS-a fully polarimetric experimental radar},
    year={2002},
    volume={3},
    number={},
    pages={1714-1716},
    abstract={The MEMPHIS polarimetric SAR is able to operate simultaneously at X-, Ka- and W-band. After a detailed technical description, several examples are given to demonstrate its capabilities in the side-looking mode, in forward squinted Doppler beam sharpenung (DBS) mode and with across-track interferometry. Of great importance is the polarimetric calibration which is described in some detail.},
    keywords={SAR Processing, W-Band,MEMPHIS, Airborne SAR, UAV, Fraunhofer,calibration;geophysical equipment;geophysical techniques;radar polarimetry;remote sensing by radar;synthetic aperture radar;terrain mapping;5 to 36 GHz;75 to 110 GHz;EHF;InSAR;Ka-band;MEMPHIS;SHF;W-band;X-band;across-track interferometry;calibration;forward squinted Doppler beam sharpening mode;geophysical measurement technique;land surface;polarimetric SAR;radar polarimetry;radar remote sensing;side-looking mode;synthetic aperture radar;technical description;terrain mapping;Calibration;Chirp;Frequency;Polarization;Radar antennas;Radar polarimetry;Receiving antennas;Satellite broadcasting;Synthetic aperture radar;Transmitting antennas},
    doi={10.1109/IGARSS.2002.1026230},
    ISSN={},
    month=jun,
    owner = {ofrey},
    
    }
    


  18. David Small, Detlev Kosmann, Jürgen Holzner, Hannes Raggam, Mauro Pirri, Adrian Schubert, Urs Krüttli, Wolfgang Hummelbrunner, and Martina Franke. ASAR Level 1 Geolocation. In Huguette Sawaya-Lacoste, editor, Proceedings of the Envisat Calibration Review, 2002. Keyword(s): SAR Geocoding, Calibration, Validation, Quality Assessment, ASAR, ENVISAT.
    Abstract: The localisation of ASAR products is vital to the ground segment, as overlays with independent information sources (typically in a map geometry) are only possible when the transformation between radar and map geometry is well calibrated. In this paper we describe calibration and validation steps undertaken to ensure that the transformations from radar to map geometry and back again are as accurate as possible. The ground segment of every new system must validate its geocoding chain to ensure that all parameters are treated consistently and are compatible with the product specifications. Special attention is devoted to the range and azimuth timing, as well as the orbit quality, cartographic and geodetic parameters describing the reference map projections. ASAR IMS and APS products are in the radar's native slant-range geometry. IMP, APP, IMM, APM, and WSM products are arranged in ground-range geometry. IMG and APG products are ellipsoid-geocoded (no terrain corrections applied), and delivered in map geometry. Each product type requires a slightly different calibration and validation methodology.

    @InProceedings{SmallKosHolRagPirSchuKruHumFra02:ASARGeoloc,
    Title = {{ASAR Level 1 Geolocation}},
    Author = {David Small and Detlev Kosmann and J{\"u}rgen Holzner and Hannes Raggam and Mauro Pirri and Adrian Schubert and Urs Kr{\"u}ttli and Wolfgang Hummelbrunner and Martina Franke},
    Booktitle = {Proceedings of the Envisat Calibration Review},
    Editor = {Huguette Sawaya-Lacoste},
    Url = {http://envisat.esa.int/calval/proceedings/asar/asar_15.pdf},
    Year = {2002},
    Abstract = {The localisation of ASAR products is vital to the ground segment, as overlays with independent information sources (typically in a map geometry) are only possible when the transformation between radar and map geometry is well calibrated. In this paper we describe calibration and validation steps undertaken to ensure that the transformations from radar to map geometry and back again are as accurate as possible. The ground segment of every new system must validate its geocoding chain to ensure that all parameters are treated consistently and are compatible with the product specifications. Special attention is devoted to the range and azimuth timing, as well as the orbit quality, cartographic and geodetic parameters describing the reference map projections. ASAR IMS and APS products are in the radar's native slant-range geometry. IMP, APP, IMM, APM, and WSM products are arranged in ground-range geometry. IMG and APG products are ellipsoid-geocoded (no terrain corrections applied), and delivered in map geometry. Each product type requires a slightly different calibration and validation methodology.},
    Keywords = {SAR Geocoding, Calibration, Validation, Quality Assessment, ASAR, ENVISAT},
    Pdf = {../../../docs/SmallKosHolRagPirSchuKruHumFra02.pdf} 
    }
    


  19. David Small, Adrian Schubert, Urs Krüttli, Erich Meier, and Daniel Nüesch. Preliminary Validation of ASAR Geometric Accuracy. In Proceedings of ENVISAT Validation Workshop, ESA-ESRIN, Frascati, Dec. 2002. Keyword(s): SAR Processing, SAR Geocoding, Geometric Accuracy, Geometric Calibration, Calibration, Validation, Quality Assessment, ASAR, ENVISAT.
    Abstract: We describe preliminary validation experiments performed to validate the geometric accuracy of ENVISAT ASAR data acquired in image (IM) and alternating polarisation (AP) modes. ESA?s ASAR transponders in The Netherlands were used primarily as reference locations. Corner reflectors were deployed at test sites in Switzerland for comparison, and conventional ground control points such as bridges and road intersections were also used. The location of the reference points in radar geometry was predicted based upon the reflector?s geographical position (and delay term in the case of transponders) and compared with the actual measured location in the image products. We form tentative conclusions on the residual error sources.

    @InProceedings{smallSchubertKruettliNuesch02:PrelASARGeomAccuracy,
    Title = {{Preliminary Validation of ASAR Geometric Accuracy}},
    Author = {David Small and Adrian Schubert and Urs Kr{\"u}ttli and Erich Meier and Daniel N{\"u}esch},
    Booktitle = {Proceedings of ENVISAT Validation Workshop},
    Month = {Dec.},
    Year = {2002},
    Abstract = {We describe preliminary validation experiments performed to validate the geometric accuracy of ENVISAT ASAR data acquired in image (IM) and alternating polarisation (AP) modes. ESA?s ASAR transponders in The Netherlands were used primarily as reference locations. Corner reflectors were deployed at test sites in Switzerland for comparison, and conventional ground control points such as bridges and road intersections were also used. The location of the reference points in radar geometry was predicted based upon the reflector?s geographical position (and delay term in the case of transponders) and compared with the actual measured location in the image products. We form tentative conclusions on the residual error sources.},
    Address = {ESA-ESRIN, Frascati},
    Keywords = {SAR Processing, SAR Geocoding, Geometric Accuracy, Geometric Calibration,Calibration,Validation, Quality Assessment, ASAR, ENVISAT},
    Owner = {ofrey},
    Pdf = {../../../docs/smallSchubertKruettliNuesch02.pdf} 
    }
    


  20. M. Weiss and P. Berens. Motion compensation of wideband synthetic aperture radar with a new transponder technique. In IEEE International Geoscience and Remote Sensing Symposium, 2002. IGARSS '02., volume 6, pages 3649-3651, June 2002. Keyword(s): SAR Processing, Motion Compensation, calibration, Autofocus, phased array radar, radar imaging, synthetic aperture radar, transponder, PAMIR, SAR, active transponders, calibration, coherent integration, echoes, large synthetic aperture, phased array multifunctional imaging radar, radar pulses, transponder technique, wideband synthetic aperture radar.
    Abstract: A high resolution synthetic aperture radar (SAR) system called phased array multifunctional imaging radar (PAMIR) is currently under development at FGAN. This system uses a very high bandwidth and performs a coherent integration along a large synthetic aperture. Problems in the area of calibration and motion compensation arise which can't be solved using common tools like corner reflectors. This paper describes the construction of active transponders which modulate and re-radiate radar pulses, discusses the advantages for calibration and shows how the echoes can be used for motion compensation in the SAR processing.

    @InProceedings{weissBerens2002:MoCoAutofocusTransponder,
    Title = {Motion compensation of wideband synthetic aperture radar with a new transponder technique},
    Author = {Weiss, M. and Berens, P.},
    Booktitle = {IEEE International Geoscience and Remote Sensing Symposium, 2002. IGARSS '02.},
    Doi = {10.1109/IGARSS.2002.1027279},
    Month = {jun},
    Pages = {3649--3651},
    Url = {http://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=1027279&isnumber=22041},
    Volume = {6},
    Year = {2002},
    Abstract = {A high resolution synthetic aperture radar (SAR) system called phased array multifunctional imaging radar (PAMIR) is currently under development at FGAN. This system uses a very high bandwidth and performs a coherent integration along a large synthetic aperture. Problems in the area of calibration and motion compensation arise which can't be solved using common tools like corner reflectors. This paper describes the construction of active transponders which modulate and re-radiate radar pulses, discusses the advantages for calibration and shows how the echoes can be used for motion compensation in the SAR processing.},
    Keywords = {SAR Processing, Motion Compensation, calibration, Autofocus, phased array radar, radar imaging, synthetic aperture radar, transponder, PAMIR, SAR, active transponders, calibration, coherent integration, echoes, large synthetic aperture, phased array multifunctional imaging radar, radar pulses, transponder technique, wideband synthetic aperture radar},
    Owner = {ofrey},
    Pdf = {../../../docs/weissBerens2002.pdf} 
    }
    


  21. Charles L. Werner, Urs Wegmuller, and Tazio Strozzi. Processing Strategies for Phase Unwrapping for InSAR Applications. In Proc. of EUSAR 2002 - 4th European Conference on Synthetic Aperture Radar, volume 1, pages 353-356, 2002. Keyword(s): SAR Processing, Interferometry, Phase Unwrapping, Minimum Cost Flow, Branch Cut.
    Abstract: One of the most challenging aspects in the successful application of SAR interferometry (INSAR) is unwrapping the interferometric phase. The difficulties arise in attempting to find global optimization procedures with the best possible cost criteria for data that are both noisy and incomplete. Recent progress in this problem includes introduction of network flow optimization, and the use of triangular irregular networks for sparse data. Interferograms differ greatly in the difficulty to unwrap depending on the interferogram fringe complexity and correlation. We examine the characteristics of these types and present phase unwrapping strategies for each of these.

    @InProceedings{WernWegStroz02:phaseUnWrap,
    Title = {{Processing Strategies for Phase Unwrapping for InSAR Applications}},
    Author = {Charles L. Werner and Urs Wegmuller and Tazio Strozzi},
    Booktitle = {Proc. of EUSAR 2002 - 4th European Conference on Synthetic Aperture Radar},
    Pages = {353-356},
    Volume = {1},
    Year = {2002},
    Abstract = {One of the most challenging aspects in the successful application of SAR interferometry (INSAR) is unwrapping the interferometric phase. The difficulties arise in attempting to find global optimization procedures with the best possible cost criteria for data that are both noisy and incomplete. Recent progress in this problem includes introduction of network flow optimization, and the use of triangular irregular networks for sparse data. Interferograms differ greatly in the difficulty to unwrap depending on the interferogram fringe complexity and correlation. We examine the characteristics of these types and present phase unwrapping strategies for each of these.},
    Keywords = {SAR Processing, Interferometry, Phase Unwrapping, Minimum Cost Flow, Branch Cut},
    Pdf = {../../../docs/WernerWegStrozzi02.pdf} 
    }
    


  22. Xiaojian Xu and R. M. Narayanan. SAR image enhancement using noninteger Nyquist SVA technique. In Proc. IEEE Antennas and Propagation Society International Symposium, volume 4, pages 298-301, 2002. Keyword(s): SAR Processing, Apodization, Spatially Variant Apodization, SVA, ISAR, image enhancement, image resolution, inverse SAR imaging, iterative super SVA procedure, noninteger Nyquist SVA, nonlinear filtering, sidelobe level reduction, spatially variant apodization, synthetic aperture radar, iterative methods, nonlinear filters.
    Abstract: In SAR and inverse SAR (ISAR) imaging, conventional Fourier transform (FT) based image reconstruction techniques result in images with limited resolution. The down-range and cross-range resolutions of these algorithms are inversely proportional to the radar signal waveform bandwidth and to the synthetic aperture size, respectively. On the other hand, when modem spectral estimation methods are applied to radar imaging, these nonlinear techniques, usually called super resolution algorithms, offer improved resolution, better contrast, and reduced speckle. Spatially variant apodization (SVA) is a nonlinear filtering operation which significantly reduces the sidelobe levels without degrading mainlobe resolution of the sinc impulse response. In this work, we propose a modified version of noninteger Nyquist SVA and develop an iterative super SVA procedure for SAR and ISAR image enhancement. The proposed technique was successfully applied to various SAR/ISAR images.

    @InProceedings{xiaojianNarayanan2002:Apodization,
    author = {Xiaojian Xu and Narayanan, R. M.},
    booktitle = {Proc. IEEE Antennas and Propagation Society International Symposium},
    title = {{SAR} image enhancement using noninteger {N}yquist {SVA} technique},
    year = {2002},
    pages = {298-301},
    volume = {4},
    abstract = {In SAR and inverse SAR (ISAR) imaging, conventional Fourier transform (FT) based image reconstruction techniques result in images with limited resolution. The down-range and cross-range resolutions of these algorithms are inversely proportional to the radar signal waveform bandwidth and to the synthetic aperture size, respectively. On the other hand, when modem spectral estimation methods are applied to radar imaging, these nonlinear techniques, usually called super resolution algorithms, offer improved resolution, better contrast, and reduced speckle. Spatially variant apodization (SVA) is a nonlinear filtering operation which significantly reduces the sidelobe levels without degrading mainlobe resolution of the sinc impulse response. In this work, we propose a modified version of noninteger Nyquist SVA and develop an iterative super SVA procedure for SAR and ISAR image enhancement. The proposed technique was successfully applied to various SAR/ISAR images.},
    doi = {10.1109/APS.2002.1016982},
    keywords = {SAR Processing, Apodization, Spatially Variant Apodization, SVA, ISAR, image enhancement, image resolution, inverse SAR imaging, iterative super SVA procedure, noninteger Nyquist SVA, nonlinear filtering, sidelobe level reduction, spatially variant apodization, synthetic aperture radar, iterative methods, nonlinear filters},
    
    }
    


Internal reports

  1. ASAR-Cal-Val-Team. Quality Measurements Definition for ASAR Level 1 Products. Technical report Iss. 1, ESA, Mar. 2002. Keyword(s): ENVISAT, ASAR, Product Calibration, Calibration, Quality Assessment, Quality Measures, ISLR, PSLR, SSLR, Level 1 Products, SAR, ASAR, ENVISAT, Calibration, Validation, Quality Measures.
    Abstract: The activities to verify and calibrate ASAR products during the ENVISAT Commissioning Phase (C.P.) will be carried out by the ASAR CAL/VAL team members at different centres and in some cases, using different product analysis tools. It is therefore important to establish the methodology for deriving all the quality parameters so that results from different team members are completely consistent. This document describes the procedures to be followed during the C.P. for measuring the ASAR product quality parameters on Level I products.

    @TechReport{qualityMeasuresASAR:IMGQUALITY,
    Title = {{Quality Measurements Definition for ASAR Level 1 Products}},
    Author = {ASAR-Cal-Val-Team},
    Institution = {ESA},
    Month = {Mar.},
    Number = {Iss. 1},
    Year = {2002},
    Abstract = {The activities to verify and calibrate ASAR products during the ENVISAT Commissioning Phase (C.P.) will be carried out by the ASAR CAL/VAL team members at different centres and in some cases, using different product analysis tools. It is therefore important to establish the methodology for deriving all the quality parameters so that results from different team members are completely consistent. This document describes the procedures to be followed during the C.P. for measuring the ASAR product quality parameters on Level I products.},
    Keyword = {ENVISAT, ASAR, Product Calibration, Calibration, Quality Assessment, Quality Measures, ISLR, PSLR, SSLR, Level 1 Products, SAR},
    Keywords = {ASAR, ENVISAT, Calibration, Validation, Quality Measures},
    Owner = {ofrey},
    Pdf = {../../../docs/qualityMeasuresASAR.pdf},
    Publisher = {ESRIN, ESA} 
    }
    


Miscellaneous

  1. Betlem Rosich. Preliminary Doppler Analysis on ASAR Products, 2002. Keyword(s): SAR Processing, Doppler Centroid, Doppler Centroid Estimation, Clutterlock, ASAR, ENVISAT.
    Abstract: This paper summarised the different Doppler estimation algorithms used in PF-ASAR for the different modes, how this information appears on the ASAR products and provides a first comparisons between measured and expected Doppler as well as a preliminary estimation of the in-flight antenna miss-pointing based on wave mode data products.

    @Misc{rosich:asarDoppler,
    Title = {{Preliminary Doppler Analysis on ASAR Products}},
    Author = {Betlem Rosich},
    Url = {http://envisat.esa.int/calval/proceedings/asar/asar_09.pdf},
    Year = {2002},
    Abstract = {This paper summarised the different Doppler estimation algorithms used in PF-ASAR for the different modes, how this information appears on the ASAR products and provides a first comparisons between measured and expected Doppler as well as a preliminary estimation of the in-flight antenna miss-pointing based on wave mode data products.},
    Keywords = {SAR Processing, Doppler Centroid, Doppler Centroid Estimation, Clutterlock, ASAR, ENVISAT},
    Pdf = {../../../docs/asarDopplerReview.pdf} 
    }
    


  2. David T. Sandwell. SAR Image Formation: ERS SAR Processor Coded in Matlab. Note: Lecture Notes - Radar and Sonar Interferometry, 2002. Keyword(s): SAR, SAR Processing, Digitizing, ERS, MATLAB, Range-Doppler, Range Compression, Range Migration, Azimuth Processing, SLC, Raw Data, Parameter Files, Squinted SAR, Example Processor.
    @Unpublished{San02d:SAR,
    Title = {{SAR Image Formation: ERS SAR Processor Coded in Matlab}},
    Author = {David T. Sandwell},
    Note = {Lecture Notes - Radar and Sonar Interferometry},
    Url = {http://topex.ucsd.edu/insar},
    Year = {2002},
    Comment = {++ MATLAB SAR processor description and code. It is used in a lecture at the University of California in San Diego. The code is printed in full in the appendix of the paper.},
    Keywords = {SAR, SAR Processing, Digitizing, ERS, MATLAB, Range-Doppler, Range Compression, Range Migration, Azimuth Processing, SLC, Raw Data, Parameter Files, Squinted SAR, Example Processor},
    Pdf = {../../../docs/sandwell02.pdf} 
    }
    


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Please note that access to full text PDF versions of papers is restricted to the Chair of Earth Observation and Remote Sensing, Institute of Environmental Engineering, ETH Zurich.
Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright.

This collection of SAR literature is far from being complete.
It is rather a collection of papers which I store in my literature data base. Hence, the list of publications under PUBLICATIONS OF AUTHOR'S NAME should NOT be mistaken for a complete bibliography of that author.




Last modified: Mon Feb 1 16:39:00 2021
Author: Othmar Frey, Earth Observation and Remote Sensing, Institute of Environmental Engineering, Swiss Federal Institute of Technology - ETH Zurich .


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