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## Publications of year 2001

### Books and proceedings

1. Ramon F. Hanssen. Radar interferometry: data interpretation and error analysis. Kluwer Academic Publishers, 2001. Keyword(s): SAR Processing, SAR, Interferometry, InSAR, Error Analysis, InSAR Error Analysis, Teaching Material, Tutorial.
@Book{RadarInterferometryBookRamonHanssen2002,
title = {Radar interferometry: data interpretation and error analysis},
year = {2001},
author = {Hanssen, Ramon F.},
doi = {10.1007/0-306-47633-9},
keywords = {SAR Processing, SAR, Interferometry, InSAR, Error Analysis, InSAR Error Analysis, Teaching Material,Tutorial},
owner = {ofrey},

}


### Thesis

1. Andreas Reigber. Airborne Polarimetric SAR Tomography. PhD thesis, University of Stuttgart, 2001. Keyword(s): SAR Processing, SAR Tomography, Tomography, Polarimettric SAR, Pol-InSAR, L-Band, E-SAR.
@PhdThesis{reigberDiss2001:Tomo,
Title = {Airborne Polarimetric SAR Tomography},
Author = {Andreas Reigber},
Url = {http://www.cv.tu-berlin.de/~anderl/papers/dissertation_reigber.pdf},
Year = {2001},
Keywords = {SAR Processing, SAR Tomography, Tomography, Polarimettric SAR, Pol-InSAR, L-Band, E-SAR},
Owner = {ofrey},
Pdf = {../../../docs/dissertation_reigber01.pdf},
School = {University of Stuttgart}
}


### Articles in journal or book chapters

1. Curtis W. Chen and Howard A. Zebker. Two-dimensional phase unwrapping with use of statistical models for cost functions in nonlinear optimization. J. Opt. Soc. Am. A, 18(2):338-351, February 2001. Keyword(s): SAR Processing, phase unwrapping, SNAPHU, SAR Interferometry, InSAR, Synthetic aperture radar, Phase.
 Abstract: Interferometric radar techniques often necessitate two-dimensional (2-D) phase unwrapping, defined here as the estimation of unambiguous phase data from a 2-D array known only modulo 2$\pi$ rad. We develop a maximum a posteriori probability (MAP) estimation approach for this problem, and we derive an algorithm that approximately maximizes the conditional probability of its phase-unwrapped solution given observable quantities such as wrapped phase, image intensity, and interferogram coherence. Examining topographic and differential interferometry separately, we derive simple, working models for the joint statistics of the estimated and the observed signals. We use generalized, nonlinear cost functions to reflect these probability relationships, and we employ nonlinear network-flow techniques to approximate MAP solutions. We apply our algorithm both to a topographic interferogram exhibiting rough terrain and layover and to a differential interferogram measuring the deformation from a large earthquake. The MAP solutions are complete and are more accurate than those of other tested algorithms.

@Article{chenZebkerJOptSoc2001SNAPHU2DPhaseUnwrappingCostFunctionNonlinearOptimization,
author = {Curtis W. Chen and Howard A. Zebker},
title = {Two-dimensional phase unwrapping with use of statistical models for cost functions in nonlinear optimization},
journal = {J. Opt. Soc. Am. A},
year = {2001},
volume = {18},
number = {2},
pages = {338-351},
month = feb,
abstract = {Interferometric radar techniques often necessitate two-dimensional (2-D) phase unwrapping, defined here as the estimation of unambiguous phase data from a 2-D array known only modulo 2$\pi$ rad. We develop a maximum a posteriori probability (MAP) estimation approach for this problem, and we derive an algorithm that approximately maximizes the conditional probability of its phase-unwrapped solution given observable quantities such as wrapped phase, image intensity, and interferogram coherence. Examining topographic and differential interferometry separately, we derive simple, working models for the joint statistics of the estimated and the observed signals. We use generalized, nonlinear cost functions to reflect these probability relationships, and we employ nonlinear network-flow techniques to approximate MAP solutions. We apply our algorithm both to a topographic interferogram exhibiting rough terrain and layover and to a differential interferogram measuring the deformation from a large earthquake. The MAP solutions are complete and are more accurate than those of other tested algorithms.},
doi = {10.1364/JOSAA.18.000338},
file = {:chenZebkerJOptSoc2001SNAPHU2DPhaseUnwrappingCostFunctionNonlinearOptimization.pdf:PDF},
keywords = {SAR Processing, phase unwrapping, SNAPHU, SAR Interferometry; InSAR, Synthetic aperture radar; Phase},
owner = {ofrey},
publisher = {OSA},
url = {http://josaa.osa.org/abstract.cfm?URI=josaa-18-2-338},

}


2. A. Ferretti, C. Prati, and F. Rocca. Permanent scatterers in SAR interferometry. IEEE Trans. Geosci. Remote Sens., 39(1):8-20, 2001. Keyword(s): SAR Processing, PSI, Persistent Scatterer Interferometry, Differential SAR Interferometry, Permanent scatterers, geodesy, geophysical techniques, remote sensing by radar, synthetic aperture radar, terrain mapping, topography (Earth)InSAR, SAR interferometry, atmospheric disturbance, atmospheric phase screen, differential interferometry, geodesy, geometrical decorrelation, geophysical measurement technique, land surface topography, permanent scatterer, radar remote sensing, stable natural reflector, surface deformation monitoring, synthetic aperture radar, terrain mapping, topographic profile reconstruction.
 Abstract: Temporal and geometrical decorrelation often prevents SAR interferometry from being an operational tool for surface deformation monitoring and topographic profile reconstruction. Moreover, atmospheric disturbances can strongly compromise the accuracy of the results. The authors present a complete procedure for the identification and exploitation of stable natural reflectors or permanent scatterers (PSs) starting from long temporal series of interferometric SAR images. When, as it often happens, the dimension of the PS is smaller than the resolution cell, the coherence is good even for interferograms with baselines larger than the decorrelation one, and all the available images of the ESA ERS data set can be successfully exploited. On these pixels, submeter DEM accuracy and millimetric terrain motion detection can be achieved, since atmospheric phase screen (APS) contributions can be estimated and removed. Examples are then shown of small motion measurements, DEM refinement, and APS estimation and removal in the case of a sliding area in Ancona, Italy. ERS data have been used

@Article{ferrettiPratiRocca2001:PermanentScat,
author = {Ferretti, A. and Prati, C. and Rocca, F.},
title = {{Permanent scatterers in SAR interferometry}},
journal = {IEEE Trans. Geosci. Remote Sens.},
year = {2001},
volume = {39},
number = {1},
pages = {8-20},
issn = {0196-2892},
abstract = {Temporal and geometrical decorrelation often prevents SAR interferometry from being an operational tool for surface deformation monitoring and topographic profile reconstruction. Moreover, atmospheric disturbances can strongly compromise the accuracy of the results. The authors present a complete procedure for the identification and exploitation of stable natural reflectors or permanent scatterers (PSs) starting from long temporal series of interferometric SAR images. When, as it often happens, the dimension of the PS is smaller than the resolution cell, the coherence is good even for interferograms with baselines larger than the decorrelation one, and all the available images of the ESA ERS data set can be successfully exploited. On these pixels, submeter DEM accuracy and millimetric terrain motion detection can be achieved, since atmospheric phase screen (APS) contributions can be estimated and removed. Examples are then shown of small motion measurements, DEM refinement, and APS estimation and removal in the case of a sliding area in Ancona, Italy. ERS data have been used},
doi = {10.1109/36.898661},
file = {:ferrettiPratiRocca2001_PermanentScat - Permanent Scatterers in SAR Interferometry.pdf:PDF},
keywords = {SAR Processing, PSI, Persistent Scatterer Interferometry, Differential SAR Interferometry, Permanent scatterers, geodesy, geophysical techniques, remote sensing by radar, synthetic aperture radar, terrain mapping, topography (Earth)InSAR, SAR interferometry, atmospheric disturbance, atmospheric phase screen, differential interferometry, geodesy, geometrical decorrelation, geophysical measurement technique, land surface topography, permanent scatterer, radar remote sensing, stable natural reflector, surface deformation monitoring, synthetic aperture radar, terrain mapping, topographic profile reconstruction},
pdf = {../../../docs/ferrettiPratiRocca2001.pdf},
url = {http://ieeexplore.ieee.org/iel5/36/19440/00898661.pdf},

}


3. R. Lanari, M. Tesauro, E. Sansosti, and G. Fornaro. Spotlight SAR data focusing based on a two-step processing approach. IEEE Transactions on Geoscience and Remote Sensing, 39(9):1993 -2004, September 2001. Keyword(s): SPECAN algorithm, azimuth spectral folding, data focusing, data-focusing algorithm, deramping, geophysical measurement technique, high bandwidth transmitted chirp signals, land surface, radar remote sensing, space-invariant azimuth filtering, space-variant characteristics, spaceborne radar, spectral analysis, spotlight SAR, stripmap focusing, synthetic aperture radar, terrain mapping, two-step process, geophysical signal processing, geophysical techniques, radar imaging, remote sensing by radar, spaceborne radar, synthetic aperture radar, terrain mapping.
 Abstract: The authors present a new spotlight SAR data-focusing algorithm based on a two-step processing strategy that combines the advantages of two commonly adopted processing approaches: the efficiency of SPECAN algorithms and the precision of stripmap focusing techniques. The first step of the proposed algorithm implements a linear and space-invariant azimuth filtering that is carried out via a deramping-based technique representing a simplified version of the SPECAN approach. This operation allows the authors to perform a bulk azimuth raw data compression and to achieve a pixel spacing smaller than (or equal to) the expected azimuth resolution of the fully focused image. Thus, the azimuth spectral folding phenomenon, typically affecting the spotlight data, is overcome, and the space-variant characteristics of the stripmap system transfer function are preserved. Accordingly, the residual and precise focusing of the SAR data is achieved by applying a conventional stripmap processing procedure requiring a minor modification and implemented in the frequency domain. The extension of the proposed technique to the case of high bandwidth transmitted chirp signals is also discussed. Experiments carried out on real and simulated data confirm the validity of the presented approach, which is mainly focused on spaceborne systems

@Article{951090,
author = {Lanari, R. and Tesauro, M. and Sansosti, E. and Fornaro, G.},
journal = {IEEE Transactions on Geoscience and Remote Sensing},
title = {Spotlight SAR data focusing based on a two-step processing approach},
year = {2001},
issn = {0196-2892},
month = {sep},
number = {9},
pages = {1993 -2004},
volume = {39},
abstract = {The authors present a new spotlight SAR data-focusing algorithm based on a two-step processing strategy that combines the advantages of two commonly adopted processing approaches: the efficiency of SPECAN algorithms and the precision of stripmap focusing techniques. The first step of the proposed algorithm implements a linear and space-invariant azimuth filtering that is carried out via a deramping-based technique representing a simplified version of the SPECAN approach. This operation allows the authors to perform a bulk azimuth raw data compression and to achieve a pixel spacing smaller than (or equal to) the expected azimuth resolution of the fully focused image. Thus, the azimuth spectral folding phenomenon, typically affecting the spotlight data, is overcome, and the space-variant characteristics of the stripmap system transfer function are preserved. Accordingly, the residual and precise focusing of the SAR data is achieved by applying a conventional stripmap processing procedure requiring a minor modification and implemented in the frequency domain. The extension of the proposed technique to the case of high bandwidth transmitted chirp signals is also discussed. Experiments carried out on real and simulated data confirm the validity of the presented approach, which is mainly focused on spaceborne systems},
doi = {10.1109/36.951090},
keywords = {SPECAN algorithm;azimuth spectral folding;data focusing;data-focusing algorithm;deramping;geophysical measurement technique;high bandwidth transmitted chirp signals;land surface;radar remote sensing;space-invariant azimuth filtering;space-variant characteristics;spaceborne radar;spectral analysis;spotlight SAR;stripmap focusing;synthetic aperture radar;terrain mapping;two-step process;geophysical signal processing;geophysical techniques;radar imaging;remote sensing by radar;spaceborne radar;synthetic aperture radar;terrain mapping},

}


4. R. Lanari, S. Zoffoli, E. Sansosti, G. Fornaro, and F. Serafino. New approach for hybrid strip-map/spotlight SAR data focusing. IEE Proceedings - Radar, Sonar and Navigation, 148(6):363 -372, December 2001. Keyword(s): SAR data processing, azimuth convolution, azimuth data filtering, azimuth resolution, chirp signal, focused SAR images, generalised processing code, hybrid acquisition mode, hybrid strip-map/spotlight SAR, microwave image generation, spacebome systems, spotlight SAR data processing, strip-map processing, two-step focusing technique, convolution, filtering theory, image resolution, radar imaging, radar resolution, spaceborne radar, synthetic aperture radar.
 Abstract: A new algorithm is presented for processing SAR data acquired in the hybrid strip-map/spotlight SAR configuration whose acquisition mode allows the generation of microwave images with an azimuth resolution better than that obtained in the strip-map case and with an imaged area larger than that achieved in the spotlight operation. The algorithm extends the focusing capability of conventional strip-map processing techniques to the hybrid SAR data; this result is achieved by generalising a previously proposed two-step focusing technique for spotlight SAR data processing, the spotlight mode being a particular case of the more general hybrid one. The key point of the procedure is the first filtering step which implements an azimuth convolution between the raw data and a chirp signal whose rate is selected, in the generalised approach, depending on the characteristics of the hybrid acquisition mode. Following this stage, standard strip-map processing procedures can be used to implement the second processing step, leading to fully focused SAR images. The algorithm, mainly oriented to spaceborne systems, is simple and efficient and allows the design of a generalised processing code suitable for data acquired in the hybrid strip-map/spotlight SAR configuration including the strip-map and spotlight modes as special cases. Experiments carried out on simulated data clarify the rationale of the method and confirm its validity

@Article{980764,
Title = {New approach for hybrid strip-map/spotlight SAR data focusing},
Author = {Lanari, R. and Zoffoli, S. and Sansosti, E. and Fornaro, G. and Serafino, F.},
Doi = {10.1049/ip-rsn:20010662},
ISSN = {1350-2395},
Month = {dec},
Number = {6},
Pages = {363 -372},
Volume = {148},
Year = {2001},
Abstract = {A new algorithm is presented for processing SAR data acquired in the hybrid strip-map/spotlight SAR configuration whose acquisition mode allows the generation of microwave images with an azimuth resolution better than that obtained in the strip-map case and with an imaged area larger than that achieved in the spotlight operation. The algorithm extends the focusing capability of conventional strip-map processing techniques to the hybrid SAR data; this result is achieved by generalising a previously proposed two-step focusing technique for spotlight SAR data processing, the spotlight mode being a particular case of the more general hybrid one. The key point of the procedure is the first filtering step which implements an azimuth convolution between the raw data and a chirp signal whose rate is selected, in the generalised approach, depending on the characteristics of the hybrid acquisition mode. Following this stage, standard strip-map processing procedures can be used to implement the second processing step, leading to fully focused SAR images. The algorithm, mainly oriented to spaceborne systems, is simple and efficient and allows the design of a generalised processing code suitable for data acquired in the hybrid strip-map/spotlight SAR configuration including the strip-map and spotlight modes as special cases. Experiments carried out on simulated data clarify the rationale of the method and confirm its validity},
Keywords = {SAR data processing;azimuth convolution;azimuth data filtering;azimuth resolution;chirp signal;focused SAR images;generalised processing code;hybrid acquisition mode;hybrid strip-map/spotlight SAR;microwave image generation;spacebome systems;spotlight SAR data processing;strip-map processing;two-step focusing technique;convolution;filtering theory;image resolution;radar imaging;radar resolution;spaceborne radar;synthetic aperture radar}
}


5. Fabrizio Lombardini and Hugh D. Griffiths. Optimum and Suboptimum Estimator Performance for Multibaseline InSAR. EUSAR 2000 Special Issue, Frequenz, Zeitschrift für Telekommunikation (Journal of Telecommunications), 55:114-118, March 2001. Keyword(s): SAR Processing, Interferometry, Multibaseline InSAR, Model-Based Interferometric Processing.
 Abstract: Multibaseline methods have been recently proposed to reduce problems of phase ambiguity and data noise in SAR interferometry for topographic mapping. Both phase-only interferometry and direct processing of the complex multibaseline data have been considered. In this paper, two non-model based multibaseline estimators and two recently proposed model based algorithms are discussed and compared in terms of statistical accuracy of the reduced-ambiguity phase estimate. lt is shown that model-based processing of the complex multibaseline data can be significantly more efficient than the other methods.

@Article{lombardiniFrequenz01:MultibaselineInSAR,
Title = {{Optimum and Suboptimum Estimator Performance for Multibaseline InSAR}},
Author = {Fabrizio Lombardini and Hugh D. Griffiths},
Month = mar,
Pages = {114-118},
Volume = {55},
Year = {2001},
Abstract = {Multibaseline methods have been recently proposed to reduce problems of phase ambiguity and data noise in SAR interferometry for topographic mapping. Both phase-only interferometry and direct processing of the complex multibaseline data have been considered. In this paper, two non-model based multibaseline estimators and two recently proposed model based algorithms are discussed and compared in terms of statistical accuracy of the reduced-ambiguity phase estimate. lt is shown that model-based processing of the complex multibaseline data can be significantly more efficient than the other methods.},
Journal = {EUSAR 2000 Special Issue, Frequenz, Zeitschrift f{\"u}r Telekommunikation (Journal of Telecommunications)},
Keywords = {SAR Processing, Interferometry, Multibaseline InSAR, Model-Based Interferometric Processing},
Pdf = {../../../docs/lombardiniFrequenz01.pdf}
}


6. X. Luo, Lars M. H. Ulander, J. Askne, G. Smith, and Per-Olov Frölind. RFI Suppression in Ultra-Wideband SAR Systems Using LMS Filters in Frequency Domain. Electronics Letters, 37(4):241-243, February 2001. Keyword(s): SAR Processing, RFI Suppression, Back-Projection, Ultra-Wideband SAR, VHF SAR, CARABAS, Airborne SAR.
 Abstract: A least-mean-square algorithm in the frequency domain, with amplitude normalisation, is proposed to remove narrowband radio frequency interference in low-frequency ultra-wideband synthetic aperture radar systems. The performance of the algorithm was tested on experimental data acquired with the CARABAS system

@Article{LuoUlandAskSmiFro01:RFI,
author = {X. Luo and Lars M. H. Ulander and J. Askne and G. Smith and Per-Olov Fr{\"o}lind},
title = {{RFI Suppression in Ultra-Wideband SAR Systems Using LMS Filters in Frequency Domain}},
journal = {Electronics Letters},
year = {2001},
volume = {37},
number = {4},
pages = {241-243},
month = Feb,
abstract = {A least-mean-square algorithm in the frequency domain, with amplitude normalisation, is proposed to remove narrowband radio frequency interference in low-frequency ultra-wideband synthetic aperture radar systems. The performance of the algorithm was tested on experimental data acquired with the CARABAS system},
keywords = {SAR Processing, RFI Suppression, Back-Projection, Ultra-Wideband SAR, VHF SAR, CARABAS, Airborne SAR},
url = {http://ieeexplore.ieee.org/iel5/2220/19607/00907545.pdf},

}


7. Andrea Monti-Guarnieri and Pietro Guccione. Optimal Focusing for Low Resolution ScanSAR. IEEE Transactions on Geoscience and Remote Sensing, 39(3):479-491, March 2001. Keyword(s): SAR Processing, ScanSAR, Focusing.
 Abstract: This paper deals with the focusing of low resolution ScanSAR data, for both detected amplitude images and interferometric applications. The SAR reference is exploited to achieve ScanSAR focusing in conventional techniques. Such techniques provide quite effective compensation of the azimuth antenna pattern (AAP) (e.g., no scalloping) when the azimuth time-bandwidth product (TBP ) of the ScanSAR echo is large, but fail to do so as the burst shortens, being reduced to an ineffective weighting of the output. The result is an azimuth varying distortion of the focused impulse responses, a distortion that is partly compensated for in the multilook average (not available for interferometric applications) at the price of a reduction in the processed Doppler bandwidth. This paper proposes quite a different approach. A set of short kernels, each suitable for focusing at a specific azimuth bin, has been optimized to reconstruct source reflectivity in the minimum mean square error (MMSE) sense. That pseudoinversion converges to the conventional focusing when the burst extent is large and for short bursts, edge effects are accounted for. These azimuth-varying kernels can be suitably tuned to meet constraints in the resolution/sidelobes trade-off and have proved capable of providingfairly undistorted output and fine resolution. They better exploit the available Doppler bandwidth, maximizing the number of looks and the interferometric quality. A decomposition is suggested that implements the inverse operator as a fast preprocessing to be followed by a conventional ScanSAR processor.

@Article{monti01:optFocus,
Title = {{Optimal Focusing for Low Resolution ScanSAR}},
Author = {Andrea Monti-Guarnieri and Pietro Guccione},
Month = mar,
Number = {3},
Pages = {479-491},
Url = {http://ieeexplore.ieee.org/iel5/36/19663/00911107.pdf},
Volume = {39},
Year = {2001},
Abstract = {This paper deals with the focusing of low resolution ScanSAR data, for both detected amplitude images and interferometric applications. The SAR reference is exploited to achieve ScanSAR focusing in conventional techniques. Such techniques provide quite effective compensation of the azimuth antenna pattern (AAP) (e.g., no scalloping) when the azimuth time-bandwidth product (TBP ) of the ScanSAR echo is large, but fail to do so as the burst shortens, being reduced to an ineffective weighting of the output. The result is an azimuth varying distortion of the focused impulse responses, a distortion that is partly compensated for in the multilook average (not available for interferometric applications) at the price of a reduction in the processed Doppler bandwidth. This paper proposes quite a different approach. A set of short kernels, each suitable for focusing at a specific azimuth bin, has been optimized to reconstruct source reflectivity in the minimum mean square error (MMSE) sense. That pseudoinversion converges to the conventional focusing when the burst extent is large and for short bursts, edge effects are accounted for. These azimuth-varying kernels can be suitably tuned to meet constraints in the resolution/sidelobes trade-off and have proved capable of providingfairly undistorted output and fine resolution. They better exploit the available Doppler bandwidth, maximizing the number of looks and the interferometric quality. A decomposition is suggested that implements the inverse operator as a fast preprocessing to be followed by a conventional ScanSAR processor.},
Journal = {IEEE Transactions on Geoscience and Remote Sensing},
Keywords = {SAR Processing, ScanSAR, Focusing},
Pdf = {../../../docs/optFocusingMonti.pdf}
}


8. A. Potsis, A. Reigber, J. Mittermayer, A. Moreira, and N. Uzunoglou. Sub-aperture algorithm for motion compensation improvement in wide-beam SAR data processing. Electronics Letters, 37(23):1405-1407, 2001. Keyword(s): SAR Processing, error compensation, Motion Compensation, radar imaging, Airborne SAR, synthetic aperture radar, motion compensation improvement, residual motion error compensation, strong motion errors, sub-aperture algorithm, synthetic aperture radar processing, wide-beam SAR data processing, wide-beam azimuth processing, ESAR, P-Band.
 Abstract: The effects of strong motion errors in wide-beam azimuth synthetic aperture radar (SAR) processing are analysed and discussed, using simulated data, as well as data collected by the airborne experimental SAR system of the Deutsches Zentrum fur Luft- und Raumfahrt e.V. (DLR) (E-SAR). A new sub-aperture approach for residual motion error compensation in wide-beam azimuth processing is proposed.

@Article{potsisReigberMittermayerMoreiraUzunoglou01:SubApertureMocoAlgo,
Title = {{Sub-aperture algorithm for motion compensation improvement in wide-beam SAR data processing}},
Author = {Potsis, A. and Reigber, A. and Mittermayer, J. and Moreira, A. and Uzunoglou, N.},
Number = {23},
Pages = {1405-1407},
Url = {http://ieeexplore.ieee.org/iel5/2220/20863/00966551.pdf},
Volume = {37},
Year = {2001},
Abstract = {The effects of strong motion errors in wide-beam azimuth synthetic aperture radar (SAR) processing are analysed and discussed, using simulated data, as well as data collected by the airborne experimental SAR system of the Deutsches Zentrum fur Luft- und Raumfahrt e.V. (DLR) (E-SAR). A new sub-aperture approach for residual motion error compensation in wide-beam azimuth processing is proposed.},
Journal = {Electronics Letters},
Keywords = {SAR Processing, error compensation, Motion Compensation, radar imaging, Airborne SAR, synthetic aperture radar, motion compensation improvement, residual motion error compensation, strong motion errors, sub-aperture algorithm, synthetic aperture radar processing, wide-beam SAR data processing, wide-beam azimuth processing, ESAR, P-Band},
Owner = {ofrey},
Pdf = {../../../docs/potsisReigberMittermayerMoreiraUzunoglou01.pdf}
}


9. A. Reigber. Correction of residual motion errors in airborne SAR interferometry. Electronics Letters, 37(17):1083-1084, 2001. Keyword(s): SAR Processing, airborne radar, error correction, motion compensation, radar interference, radiowave interferometry, synthetic aperture radar, airborne SAR interferometry, airborne repeat pass interferometric SAR data, interferometric phase, residual motion compensation errors, residual motion error correction, uncompensated motion errors, Motion Compensation, Interferometry, interferometric SAR.
 Abstract: The main limitation for a wider applicability of airborne repeat pass interferometric SAR data is the presence of small uncompensated motion errors. The effect of residual motion compensation errors is addressed and a new technique to minimise their influence on the interferometric phase is proposed.

@Article{reigber01:ResMotionComp,
Title = {Correction of residual motion errors in airborne SAR interferometry},
Author = {Reigber, A.},
Number = {17},
Pages = {1083--1084},
Url = {http://ieeexplore.ieee.org/iel5/2220/20519/00948339.pdf},
Volume = {37},
Year = {2001},
Abstract = {The main limitation for a wider applicability of airborne repeat pass interferometric SAR data is the presence of small uncompensated motion errors. The effect of residual motion compensation errors is addressed and a new technique to minimise their influence on the interferometric phase is proposed.},
Journal = {Electronics Letters},
Keywords = {SAR Processing, airborne radar, error correction, motion compensation, radar interference, radiowave interferometry, synthetic aperture radar, airborne SAR interferometry, airborne repeat pass interferometric SAR data, interferometric phase, residual motion compensation errors, residual motion error correction, uncompensated motion errors, Motion Compensation, Interferometry, interferometric SAR},
Owner = {ofrey},
Pdf = {../../../docs/reigber01.pdf}
}


10. Andreas Reigber, Konstantinos P. Papathanassiou, Shane R. Cloude, and Alberto Moreira. SAR Tomography and Interferometry for the Remote Sensing of Forested Terrain. EUSAR 2000 Special Issue, Frequenz, Zeitschrift für Telekommunikation (Journal of Telecommunications), 55:119-122, March 2001. Keyword(s): SAR Processing, Tomography, SAR Tomography, Interferometry, Multi-Antenna Interferometry, Multi-Baseline Interferometry, 3D imaging, Airborne SAR, L-Band, E-SAR.
 Abstract: SAR interferometry and tomography are two potential techniques for resolving the scattering behaviour of volume scatterers. Therefore, they can be used to investigate the vertical structure of forested terrain. ln this paper we contrast the principles and the performance of the two approaches and show experimental results achieved using airborne SAR data acquired by the experimental SAR systemof DLR (E-SAR).

@Article{ReigberPapathanassiouCloudeMoreira01:Tomography,
Title = {{SAR Tomography and Interferometry for the Remote Sensing of Forested Terrain}},
Author = {Andreas Reigber and Konstantinos P. Papathanassiou and Shane R. Cloude and Alberto Moreira},
Month = mar,
Pages = {119-122},
Volume = {55},
Year = {2001},
Abstract = {SAR interferometry and tomography are two potential techniques for resolving the scattering behaviour of volume scatterers. Therefore, they can be used to investigate the vertical structure of forested terrain. ln this paper we contrast the principles and the performance of the two approaches and show experimental results achieved using airborne SAR data acquired by the experimental SAR systemof DLR (E-SAR).},
Journal = {EUSAR 2000 Special Issue, Frequenz, Zeitschrift f{\"u}r Telekommunikation (Journal of Telecommunications)},
Keywords = {SAR Processing, Tomography, SAR Tomography, Interferometry, Multi-Antenna Interferometry, Multi-Baseline Interferometry, 3D imaging, Airborne SAR, L-Band, E-SAR},
Owner = {ofrey},
Pdf = {../../../docs/ReigberPapathanassiouCloudeMoreira01.pdf}
}


11. Ludwig Rössing and Joachim H.G. Ender. Multi-Antenna SAR Tomography Using Superresolution Techniques. EUSAR 2000 Special Issue, Frequenz, Zeitschrift für Telekommunikation (Journal of Telecommunications), 55:123-128, March 2001. Keyword(s): SAR Processing, Tomography, SAR Tomography, Interferometry, Multi-Antenna Interferometry, 3D imaging, superresolution, a posteriori probability density function, Airborne SAR, X-Band, Multi-Channel X-Band, AER-II, FGAN.
 Abstract: Classical SAR interferometry provides a two-dimensional image of the surface together with a pixel-to-pixel measurement of the elevation angle of that pixel with respect to the radar antenna. The elevation angle can be transformed to a height estimate for each pixel yielding a digital elevation map. This assumes that the scattering points are distributed over a two dimensional surface and that for each azimuth-range resolution cell there is only one elevation angle. In this paper, we look for solutions for those cases, in which this assumption is invalid, i.e. where there are multiple point-like scatterers with distinct elevation angles in a single resolution cell. Using a parametric approach these distinct elevation angles can be estimated simultaneously. Since for single-pass interferometry the height resolution is mostly poor because of the limited baseline, we want to apply superresolution to get an appropriate height resolution. To achieve imaging also along the third dimension we propose a calculation of an a posteriori marginal distribution of the elevation angle. This approach is illustrated by simulation results and with airborne SAR data from the multi-channel X-band system 'AER-II'.

@Article{RoessingTomogrFrequenz01:Tomography,
Title = {{Multi-Antenna SAR Tomography Using Superresolution Techniques}},
Author = {Ludwig R{\"o}ssing and Joachim H.G. Ender},
Month = mar,
Pages = {123-128},
Volume = {55},
Year = {2001},
Abstract = {Classical SAR interferometry provides a two-dimensional image of the surface together with a pixel-to-pixel measurement of the elevation angle of that pixel with respect to the radar antenna. The elevation angle can be transformed to a height estimate for each pixel yielding a digital elevation map. This assumes that the scattering points are distributed over a two dimensional surface and that for each azimuth-range resolution cell there is only one elevation angle. In this paper, we look for solutions for those cases, in which this assumption is invalid, i.e. where there are multiple point-like scatterers with distinct elevation angles in a single resolution cell. Using a parametric approach these distinct elevation angles can be estimated simultaneously. Since for single-pass interferometry the height resolution is mostly poor because of the limited baseline, we want to apply superresolution to get an appropriate height resolution. To achieve imaging also along the third dimension we propose a calculation of an a posteriori marginal distribution of the elevation angle. This approach is illustrated by simulation results and with airborne SAR data from the multi-channel X-band system 'AER-II'.},
Journal = {EUSAR 2000 Special Issue, Frequenz, Zeitschrift f{\"u}r Telekommunikation (Journal of Telecommunications)},
Keywords = {SAR Processing, Tomography, SAR Tomography, Interferometry, Multi-Antenna Interferometry, 3D imaging, superresolution, a posteriori probability density function, Airborne SAR, X-Band, Multi-Channel X-Band, AER-II, FGAN},
Owner = {ofrey},
Pdf = {../../../docs/RoessingTomogrFrequenz01.pdf}
}


12. Mehrdad Soumekh. Wavefront-Based Synthetic Aperture Radar Signal Processing. EUSAR 2000 Special Issue, Frequenz, Zeitschrift für Telekommunikation (Journal of Telecommunications), 55:99-113, March 2001. Keyword(s): SAR Processing, Time-Domain Back-Projection, TDBP, Back-Projection, Moving Target Indication, Range Stacking Algorithm, Wavefront Reconstruction, Range Migration Algorithm, Wavenumber Domain Algorithm, omega-k, Comparison of Algorithms, Wideband SAR, Squinted SAR, FOPEN, Motion Compensation.
 Abstract: This paper is concerned with the processing of Synthetic Aperture Radar (SAR) data, using Gabor's theory of wavefront reconstruction [9]. In the framework of this theory, multidimensional digital signal processing algorithms have been developed for accurate and computationally-efficient analysis of SAR data via a single or multi processor computer. This paper exhibits the utility of the SAR wavefront signal theory and its associated digital algorithms in addressing the practical information processing issues that are encountered in high-resolution and/or specialized SAR systems. We present results from two modern SAR systems. One system is the United States Navy P-3 ultra wideband UHF stripmap SAR that is intended for imaging man-made targets hidden under foliage (FOliage PENetrating, FOPEN, SAR). The other system is a high-resolution X-band spotlight SAR that is operated in an along-track monopulse, mode (single transmitter and dual receivers) for Ground Moving Target Indication (GMTI).

@Article{soumekhFrequenz01:Wavefront,
Title = {{Wavefront-Based Synthetic Aperture Radar Signal Processing}},
Month = mar,
Pages = {99-113},
Volume = {55},
Year = {2001},
Abstract = {This paper is concerned with the processing of Synthetic Aperture Radar (SAR) data, using Gabor's theory of wavefront reconstruction [9]. In the framework of this theory, multidimensional digital signal processing algorithms have been developed for accurate and computationally-efficient analysis of SAR data via a single or multi processor computer. This paper exhibits the utility of the SAR wavefront signal theory and its associated digital algorithms in addressing the practical information processing issues that are encountered in high-resolution and/or specialized SAR systems. We present results from two modern SAR systems. One system is the United States Navy P-3 ultra wideband UHF stripmap SAR that is intended for imaging man-made targets hidden under foliage (FOliage PENetrating, FOPEN, SAR). The other system is a high-resolution X-band spotlight SAR that is operated in an along-track monopulse, mode (single transmitter and dual receivers) for Ground Moving Target Indication (GMTI).},
Comment = {At the end of page 99 several publications are mentioned that compare different SAR processing algorithms},
Journal = {EUSAR 2000 Special Issue, Frequenz, Zeitschrift f{\"u}r Telekommunikation (Journal of Telecommunications)},
Keywords = {SAR Processing, Time-Domain Back-Projection, TDBP, Back-Projection, Moving Target Indication, Range Stacking Algorithm, Wavefront Reconstruction, Range Migration Algorithm, Wavenumber Domain Algorithm, omega-k, Comparison of Algorithms, Wideband SAR, Squinted SAR, FOPEN, Motion Compensation},
Pdf = {../../../docs/soumekhFrequenz01.pdf}
}


13. Mehrdad Soumekh, David A. Nobles, Michael C. Wicks, and Gerard J. Genello. Signal Processing of Wide Bandwidth and Wide Beamwidth P-3 SAR data. IEEE Transactions on Aerospace and Electronic Systems, 37(4):1122-1141, October 2001. Keyword(s): SAR Processing, P-Band, Ultra-Wideband SAR, Time-Domain Back-Projection, TDBP, Back-Projection, RFI Suppression.
 Abstract: This research is concerned with multidimensional signal processing and image formation with FOliage PENetrating (FOPEN) airborne radar data which were collected by a Navy P-3 ultra wideband (UWB) radar in 1995. The digital signal processors that were developed for the P-3 data commonly used a radar beamwidth angle that was limited to 35 deg. Provided that the P-3 radar beamwidth angle (after slow-time FIR filtering and 6:1 decimation) was 35 deg, the P-3 signal aperture radar (SAR) system would approximately yield alias-free data in the slow-time Doppler domain. We provide an analysis here of the slow-time Doppler properties of the P-3 SAR system. This study indicates that the P-3 database possesses a 50 deg beamwidth angle within the entire [215, 730] MHz band of the P-3 radar. We show that the 50-degree beamwidth limit is imposed by the radar (radial) range swath gate; a larger beamwidth measurements would be possible with a larger range swath gate. The 50-degree beamwidth of the P-3 system results in slow-time Doppler aliasing within the frequency band of [444, 730] MHz. We outline a slow-time processing of the P-3 data to minimize the Doppler aliasing. The images which are formed via this method are shown to be superior in quality to the images which are formed via the conventional P-3 processor. In the presentation, we also introduce a method for converting the P-3 deramped (range-compressed) data into its alias-free baseband echoed data; the utility of this conversion for suppressing radio frequency interference signals is shown

@Article{soumNoblWicGen01:PBand,
Title = {{Signal Processing of Wide Bandwidth and Wide Beamwidth P-3 SAR data}},
Author = {Mehrdad Soumekh and David A. Nobles and Michael C. Wicks and Gerard J. Genello},
Month = Oct,
Number = {4},
Pages = {1122-1141},
Url = {http://ieeexplore.ieee.org/iel5/7/21073/00976954.pdf},
Volume = {37},
Year = {2001},
Abstract = {This research is concerned with multidimensional signal processing and image formation with FOliage PENetrating (FOPEN) airborne radar data which were collected by a Navy P-3 ultra wideband (UWB) radar in 1995. The digital signal processors that were developed for the P-3 data commonly used a radar beamwidth angle that was limited to 35 deg. Provided that the P-3 radar beamwidth angle (after slow-time FIR filtering and 6:1 decimation) was 35 deg, the P-3 signal aperture radar (SAR) system would approximately yield alias-free data in the slow-time Doppler domain. We provide an analysis here of the slow-time Doppler properties of the P-3 SAR system. This study indicates that the P-3 database possesses a 50 deg beamwidth angle within the entire [215, 730] MHz band of the P-3 radar. We show that the 50-degree beamwidth limit is imposed by the radar (radial) range swath gate; a larger beamwidth measurements would be possible with a larger range swath gate. The 50-degree beamwidth of the P-3 system results in slow-time Doppler aliasing within the frequency band of [444, 730] MHz. We outline a slow-time processing of the P-3 data to minimize the Doppler aliasing. The images which are formed via this method are shown to be superior in quality to the images which are formed via the conventional P-3 processor. In the presentation, we also introduce a method for converting the P-3 deramped (range-compressed) data into its alias-free baseband echoed data; the utility of this conversion for suppressing radio frequency interference signals is shown},
Journal = {IEEE Transactions on Aerospace and Electronic Systems},
Keywords = {SAR Processing, P-Band, Ultra-Wideband SAR, Time-Domain Back-Projection, TDBP, Back-Projection, RFI Suppression},
Pdf = {../../../docs/soumekhNoblesWicksGenello01.pdf}
}


### Conference articles

1. Richard Abrahamsson, Jian Li, Petre Stoica, and Gunnar Thordarson. Sensitivity of two autofocus algorithms to spatially variant phase errors. In E. G. Zelnio, editor, Proceedings of SPIE Vol. 5788, volume 4382 of Presented at the Society of Photo-Optical Instrumentation Engineers (SPIE) Conference, pages 29-40, August 2001. Keyword(s): SAR Processing, Phase Gradient Autofocus, PGA, AUTOCLEAN, CLEAN, Polar Format Algorithm, Autofocus, Residual Motion Errors, Motion Errors, Motion Compensation, MoComp, Motion Through Resolution Cells, Spatially Variant Phase Errors, Airborne SAR.
 Abstract: In this paper we study the performance of two existing autofocus algorithms in a difficult SAR scenario. One algorithm is the well known phase gradient autofocus (PGA) algorithm and the other is the more recent AUTOCLEAN. The latter was introduced particularly with ISAR autofocus of a small target in mind and has been shown to outperform the PGA when range misalignment is present. This was expected as AUTOCLEAN, as opposed to PGA, has a built-in ability to compensate for range misalignment. In most available studies of the above autofocus algorithms spatially variant phase errors are absent or insignificant. The data used here is far-field SAR data collected over a large range of aspect angles. The target area is large, hence significant motion through resolution cells (MTRC) occurs due to target scene rotation. The polar format algorithm (PFA) is applied prior to autofocus to handle MTRC and compensate for off-track platform motion. However, the platform motion measurements used in PFA are not precise enough to compensate for the off-track motion and left after PFA are phase errors corrupting the data. These phase errors are spatially variant due to the large target scene and this violates the models for the autofocus algorithms above. This in contrast with the previously mentioned studies. We show that the performances of the autofocus algorithms considered are much deteriorated by the presence of spatially variant phase error but in different ways since the averaging of the phase error estimates is made differently in the two algorithms. Based on our numerical study of the two autofocus methods we try to rank them with respect to their sensitivity to spatially variant phase errors.

@InProceedings{abrahamssonLiStoicaThordarson2001:PGAandAUTOCLEAN,
Title = {{Sensitivity of two autofocus algorithms to spatially variant phase errors}},
Author = {{Abrahamsson}, Richard and {Li}, Jian and {Stoica}, Petre and {Thordarson}, Gunnar},
Booktitle = {Proceedings of SPIE Vol. 5788},
Editor = {{Zelnio}, E.~G.},
Month = {aug},
Pages = {29-40},
Series = {Presented at the Society of Photo-Optical Instrumentation Engineers (SPIE) Conference},
Url = {http://spiedl.aip.org/getpdf/servlet/GetPDFServlet?filetype=pdf&id=PSISDG004382000001000029000001&idtype=cvips&prog=normal},
Volume = {4382},
Year = {2001},
Abstract = {In this paper we study the performance of two existing autofocus algorithms in a difficult SAR scenario. One algorithm is the well known phase gradient autofocus (PGA) algorithm and the other is the more recent AUTOCLEAN. The latter was introduced particularly with ISAR autofocus of a small target in mind and has been shown to outperform the PGA when range misalignment is present. This was expected as AUTOCLEAN, as opposed to PGA, has a built-in ability to compensate for range misalignment. In most available studies of the above autofocus algorithms spatially variant phase errors are absent or insignificant. The data used here is far-field SAR data collected over a large range of aspect angles. The target area is large, hence significant motion through resolution cells (MTRC) occurs due to target scene rotation. The polar format algorithm (PFA) is applied prior to autofocus to handle MTRC and compensate for off-track platform motion. However, the platform motion measurements used in PFA are not precise enough to compensate for the off-track motion and left after PFA are phase errors corrupting the data. These phase errors are spatially variant due to the large target scene and this violates the models for the autofocus algorithms above. This in contrast with the previously mentioned studies. We show that the performances of the autofocus algorithms considered are much deteriorated by the presence of spatially variant phase error but in different ways since the averaging of the phase error estimates is made differently in the two algorithms. Based on our numerical study of the two autofocus methods we try to rank them with respect to their sensitivity to spatially variant phase errors.},
Keywords = {SAR Processing, Phase Gradient Autofocus, PGA, AUTOCLEAN, CLEAN, Polar Format Algorithm, Autofocus, Residual Motion Errors, Motion Errors, Motion Compensation, MoComp, Motion Through Resolution Cells, Spatially Variant Phase Errors, Airborne SAR},
Owner = {ofrey},
Pdf = {../../../docs/abrahamssonLiStoicaThordarson2001.pdf}
}


2. Arnold Barmettler, Erich Meier, and Daniel Nüesch. Development of an Ultra-Wideband SAR Processor. In CEOS SAR Workshop 2001, April 2001. Keyword(s): SAR Processing, Time-Domain Back-Projection, Back-Projection, Ultra-Wideband SAR, VHF SAR, CARABAS, Airborne SAR.
 Abstract: Ultra-wideband SAR (UWB) has a high potential for applications because it makes high-resolution low-frequency imaging radar feasible. In combination with other SAR frequency bands, topographic or even tomographic mapping will be possible and geophysical parameters determinable. RSL has its own SAR processor for frequency bands from P- to X-band for various space- and airborne SAR sensors. For the processing of VHF UWB data, a new module for azimuth focusing was developed, due to the special system requirements at these wavelengths. We present first results from RSL's VHF processing chain based upon rangecompressed data from the Swedish CARABAS sensor system.

@InProceedings{BarmettMeierNuesch01:Backproj,
Title = {{Development of an Ultra-Wideband SAR Processor}},
Author = {Arnold Barmettler and Erich Meier and Daniel N{\"u}esch},
Booktitle = {CEOS SAR Workshop 2001},
Month = apr,
Url = {http://www.geo.uzh.ch/rsl/research/SARLab/uwb/ceos2001.Tokyo.Barmettler-et-al.pdf},
Year = {2001},
Abstract = {Ultra-wideband SAR (UWB) has a high potential for applications because it makes high-resolution low-frequency imaging radar feasible. In combination with other SAR frequency bands, topographic or even tomographic mapping will be possible and geophysical parameters determinable. RSL has its own SAR processor for frequency bands from P- to X-band for various space- and airborne SAR sensors. For the processing of VHF UWB data, a new module for azimuth focusing was developed, due to the special system requirements at these wavelengths. We present first results from RSL's VHF processing chain based upon rangecompressed data from the Swedish CARABAS sensor system.},
Keywords = {SAR Processing, Time-Domain Back-Projection, Back-Projection, Ultra-Wideband SAR, VHF SAR, CARABAS, Airborne SAR},
Pdf = {../../../docs/BarmettMeierNuesch01.pdf}
}


3. Matthew C. Cobb and James H. McClellan. Omega-k Quadtree UWB SAR Focusing. In Proceedings of the 2001 IEEE Radar Conference, pages 311-314, May 2001. Keyword(s): SAR Processing, Wavefront Reconstruction, Wavenumber Domain Algorithm, omega-k Quadtree Processing, omega-k, Quadtree Processing, Back-Projection, Ultra-Wideband SAR, Ghost Target Elimination, FOPEN.
 Abstract: A variation on the quadtree algorithm for ultra- wideband, wide-angle (UWB-WA) SAR imaging that uses the omega-k algorithm for final stage focusing is introduced. Several signal processing techniques appropriate to the requirements of UWB-WA SAR, and that prevent errors and artifacts in the omega-k focusing will be reviewed. These techniques include spatial and temporal shifts for spotlight data, elimination of ghost targets, and adjustments needed to account for the virtual sampling of the quadtree algorithm. In order to justify these techniques, a simple Fourier-based model of the imaging problem appropriate to UWB-WA SAR is presented.

@InProceedings{CobbMcClellan01:Quadtree,
Title = {{Omega-k Quadtree UWB SAR Focusing}},
Author = {Matthew C. Cobb and James H. McClellan},
Booktitle = {Proceedings of the 2001 IEEE Radar Conference},
Month = May,
Pages = {311-314},
Url = {http://ieeexplore.ieee.org/iel5/7355/19954/00922997.pdf},
Year = {2001},
Abstract = {A variation on the quadtree algorithm for ultra- wideband, wide-angle (UWB-WA) SAR imaging that uses the omega-k algorithm for final stage focusing is introduced. Several signal processing techniques appropriate to the requirements of UWB-WA SAR, and that prevent errors and artifacts in the omega-k focusing will be reviewed. These techniques include spatial and temporal shifts for spotlight data, elimination of ghost targets, and adjustments needed to account for the virtual sampling of the quadtree algorithm. In order to justify these techniques, a simple Fourier-based model of the imaging problem appropriate to UWB-WA SAR is presented.},
Keywords = {SAR Processing, Wavefront Reconstruction, Wavenumber Domain Algorithm, omega-k Quadtree Processing, omega-k, Quadtree Processing, Back-Projection, Ultra-Wideband SAR, Ghost Target Elimination, FOPEN},
Pdf = {../../../docs/CobbMcClellan01.pdf}
}


4. Ian G. Cumming. Model-Based Doppler Estimation for Frame-Based SAR Processing. In IGARSS '01, International Geoscience and Remote Sensing Symposium, volume 6, pages 2645-2647, 2001. Keyword(s): SAR Processing, Doppler Centroid, Doppler Centroid Estimation, Clutterlock.
 Abstract: This paper presents a new method of Doppler centroid estimation whereby estimates are made over small blocks of data covering a whole frame of data, and examined for strong SNR and lack of bias. Poor estimates are rejected, and the remaining estimates are used to fit a surface model of the Doppler centroid vs. range and azimuth. The method is applied to both the fractional and integer PRF part of the centroid. A geometric model is used to constrain the model to allowable roll, pitch and yaw values of satellite attitude. The method is tested with RADARSAT-1 and SRTM/X-SAR data.

@InProceedings{Cumming:DopCentrEst,
Title = {{Model-Based Doppler Estimation for Frame-Based SAR Processing}},
Author = {Ian G. Cumming},
Booktitle = {IGARSS '01, International Geoscience and Remote Sensing Symposium},
Pages = {2645-2647},
Url = {http://ieeexplore.ieee.org/iel5/7695/21050/00978117.pdf},
Volume = {6},
Year = {2001},
Abstract = {This paper presents a new method of Doppler centroid estimation whereby estimates are made over small blocks of data covering a whole frame of data, and examined for strong SNR and lack of bias. Poor estimates are rejected, and the remaining estimates are used to fit a surface model of the Doppler centroid vs. range and azimuth. The method is applied to both the fractional and integer PRF part of the centroid. A geometric model is used to constrain the model to allowable roll, pitch and yaw values of satellite attitude. The method is tested with RADARSAT-1 and SRTM/X-SAR data.},
Keywords = {SAR Processing, Doppler Centroid, Doppler Centroid Estimation, Clutterlock},
Pdf = {../../../docs/Cumming01.pdf}
}


5. Joachim H. G. Ender. The meaning of k-space for classical and advanced SAR techniques. In International Symposium Physics in Signal and Image Processing, PSIP 2001, Marseille, pages 23-38, January 2001. Keyword(s): SAR Processing, k-Space, Airborne SAR, Bistatic SAR.
 Abstract: Synthetic aperture radar (SAR) has proven to be a powerful technique for imaging the surface of the earth and other celestial bodies with high resolution in the microwave region. As sensor a radar is used which is mounted on a moving platform - an airplane or satellite. By its motion a synthetic aperture is formed; the image is processed from the radar raw data using focusing algorithms of high complexity. Similar to SAR imaging is the technique of inverse SAR (ISAR), which allows to image turning or moving objects with a fixed radar. The k-space as the domain of the spatial Fourier transform presents an important mathematical tool for general imaging problems. As an example, in biomedical ultrasonic imaging, k-space techniques are widely used, for instance for the analysis of imaging systems and evaluation of data collection strategies, see e.g. [33]. In the field of radar imaging, the k-space can serve as a system analysis tool as well as the basis for reconstruction algorithms: Many of the phenomena arising for SAR and ISAR can be explained by analysis in the k-space. Some of the algorithms like polar reformatting are based on k-space formulation. To get a deeper insight into physical effects, it is also worthwile to look at advanced techniques like bistatic SAR in the light of k-space. On the other hand, the k-space is also a domain for the synthesis of imaging conditions: Thanks to the fast development of technical components, it will be more and more possible to create flexible waveforms and geometries, i.e.: to design the measurement configuration in the k-space opening new exciting possibilities. In this tutorial, a unified view of such techniques in terms of k-space is presented. Here, the aim of this tutorial is not to give a comprehensive summary of the numerous focussing algorithms, but to give aspects of the way of thinking in the three-dimensional Fourier domain. Though it is also possible to handle the k-space in terms of electromagnetic theory (e.g.[20]), we will concentrate to the signal-theoretical view.

@InProceedings{ender2001:kspace,
Title = {The meaning of k-space for classical and advanced {SAR} techniques},
Author = {Ender, Joachim H. G.},
Booktitle = {International Symposium Physics in Signal and Image Processing, PSIP 2001},
Month = {jan},
Pages = {23-38},
Year = {2001},
Abstract = {Synthetic aperture radar (SAR) has proven to be a powerful technique for imaging the surface of the earth and other celestial bodies with high resolution in the microwave region. As sensor a radar is used which is mounted on a moving platform - an airplane or satellite. By its motion a synthetic aperture is formed; the image is processed from the radar raw data using focusing algorithms of high complexity. Similar to SAR imaging is the technique of inverse SAR (ISAR), which allows to image turning or moving objects with a fixed radar. The k-space as the domain of the spatial Fourier transform presents an important mathematical tool for general imaging problems. As an example, in biomedical ultrasonic imaging, k-space techniques are widely used, for instance for the analysis of imaging systems and evaluation of data collection strategies, see e.g. [33]. In the field of radar imaging, the k-space can serve as a system analysis tool as well as the basis for reconstruction algorithms: Many of the phenomena arising for SAR and ISAR can be explained by analysis in the k-space. Some of the algorithms like polar reformatting are based on k-space formulation. To get a deeper insight into physical effects, it is also worthwile to look at advanced techniques like bistatic SAR in the light of k-space. On the other hand, the k-space is also a domain for the synthesis of imaging conditions: Thanks to the fast development of technical components, it will be more and more possible to create flexible waveforms and geometries, i.e.: to design the measurement configuration in the k-space opening new exciting possibilities. In this tutorial, a unified view of such techniques in terms of k-space is presented. Here, the aim of this tutorial is not to give a comprehensive summary of the numerous focussing algorithms, but to give aspects of the way of thinking in the three-dimensional Fourier domain. Though it is also possible to handle the k-space in terms of electromagnetic theory (e.g.[20]), we will concentrate to the signal-theoretical view.},
Keywords = {SAR Processing,k-Space, Airborne SAR, Bistatic SAR},
Owner = {ofrey},
Pdf = {../../../docs/ender2001.pdf},
Timestamp = {2009.11.20}
}


6. F. Gini, F. Lombardini, P. Matteucci, and L. Verrazzani. System and estimation problems for multibaseline InSAR imaging of multiple layovered reflectors. In Geoscience and Remote Sensing Symposium, 2001. IGARSS '01. IEEE 2001 International, volume 1, pages 115-117, July 2001.
@InProceedings{Gini2001,
Title = {System and estimation problems for multibaseline InSAR imaging of multiple layovered reflectors},
Author = {Gini, F. and Lombardini, F. and Matteucci, P. and Verrazzani, L.},
Booktitle = {Geoscience and Remote Sensing Symposium, 2001. IGARSS '01. IEEE 2001 International},
Month = jul,
Pages = {115--117},
Volume = {1},
Year = {2001},
Owner = {ofrey}
}


7. Xiaotao Huang, Zhimin Zhou, and Diannong Liang. Effects of RFI on UWB-SAR Using LFM Waveforms. In CIE International Conference on Radar, 2001, pages 631-633, October 2001. Keyword(s): SAR Processing, RFI Suppression, Ultra-Wideband SAR, VHF SAR.
 Abstract: The dual requirement of ultra-wide band synthetic aperture radar (UWB-SAR) for high range resolution and low frequency penetration proposes the problem of radio frequency interference (RFI) suppression. Although careful design of the receiver hardware can reduce this difficulty, a great amount of RFI will still distort the actual target returns. The effects of RFI on both of the design of hardware and the task of signal processing are studied. We focus our analysis on the basic pulse compression in linear frequency modulated (LFM) UWB-SAR. The output of a typical sinusoidal RFI after pulse compression is derived and proved to be closely related to the frequency of the RFI. Computer simulations successfully verify our conclusions.

@InProceedings{XiaoZhimDian01:RFI,
Title = {{Effects of RFI on UWB-SAR Using LFM Waveforms}},
Author = {Xiaotao Huang and Zhimin Zhou and Diannong Liang},
Booktitle = {CIE International Conference on Radar, 2001},
Month = Oct,
Pages = {631-633},
Url = {http://ieeexplore.ieee.org/iel5/7730/21220/00984797.pdf},
Year = {2001},
Abstract = {The dual requirement of ultra-wide band synthetic aperture radar (UWB-SAR) for high range resolution and low frequency penetration proposes the problem of radio frequency interference (RFI) suppression. Although careful design of the receiver hardware can reduce this difficulty, a great amount of RFI will still distort the actual target returns. The effects of RFI on both of the design of hardware and the task of signal processing are studied. We focus our analysis on the basic pulse compression in linear frequency modulated (LFM) UWB-SAR. The output of a typical sinusoidal RFI after pulse compression is derived and proved to be closely related to the frequency of the RFI. Computer simulations successfully verify our conclusions.},
Keywords = {SAR Processing, RFI Suppression, Ultra-Wideband SAR, VHF SAR},
Pdf = {../../../docs/XiaoZhimDian01.pdf}
}


8. Roger R.-Y. Lee, James S. Verdi, and Mehrdad Soumekh. Enhancements of NP-3 UHF Image Quality Using Digital Spotlighting Technique. In Proceedings of the 2001 IEEE Radar Conference, pages 1-6, May 2001. Keyword(s): SAR Processing, Wavefront Reconstruction, Wavenumber Domain Algorithm, omega-k, RFI Suppression, Subaperture Processing, Digital Spotlighting, Slow-Time Upsampling, Alias-free Processing, Quadband SAR, P-Band, X-Band, L-Band, C-Band, Airborne SAR.
 Abstract: This paper is concerned with signal processing issues that are associated with foliage penetrating (FOPEN) USA Navy NP-3 ultra-wideband (UWB) synthetic aperture radar. The digital signal processors that were developed for the NP-3 data commonly used a radar beamwidth angle that was limited to 35 degrees. Provided that the NP-3 radar beamwidth angle was 35 degrees, the NP-3 SAR system would approximately yield alias-free data in the slow-time Doppler domain. We show that the NP-3 data possess a 50-degree beamwidth angle within the entire 215-730 MHz band of the NP-3 radar that is imposed by the radar (radial) range swath gate. The 50-degree beamwidth of the NP-3 system results in slow-time Doppler aliasing within the frequency band of 444-730 MHz. We outline a slow-time processing of the NP-3 data, that we refer to as digital spotlighting and PRF upsampling, to minimize the Doppler aliasing. The digital spotlighting is also used for in-scene target calibration

@InProceedings{LeeVerdiSoumekh01:Spotlighting,
Title = {{Enhancements of NP-3 UHF Image Quality Using Digital Spotlighting Technique}},
Author = {Roger R.-Y. Lee and James S. Verdi and Mehrdad Soumekh},
Booktitle = {Proceedings of the 2001 IEEE Radar Conference},
Month = May,
Pages = {1-6},
Url = {http://ieeexplore.ieee.org/iel5/7355/19954/00922941.pdf},
Year = {2001},
Abstract = {This paper is concerned with signal processing issues that are associated with foliage penetrating (FOPEN) USA Navy NP-3 ultra-wideband (UWB) synthetic aperture radar. The digital signal processors that were developed for the NP-3 data commonly used a radar beamwidth angle that was limited to 35 degrees. Provided that the NP-3 radar beamwidth angle was 35 degrees, the NP-3 SAR system would approximately yield alias-free data in the slow-time Doppler domain. We show that the NP-3 data possess a 50-degree beamwidth angle within the entire 215-730 MHz band of the NP-3 radar that is imposed by the radar (radial) range swath gate. The 50-degree beamwidth of the NP-3 system results in slow-time Doppler aliasing within the frequency band of 444-730 MHz. We outline a slow-time processing of the NP-3 data, that we refer to as digital spotlighting and PRF upsampling, to minimize the Doppler aliasing. The digital spotlighting is also used for in-scene target calibration},
Keywords = {SAR Processing, Wavefront Reconstruction, Wavenumber Domain Algorithm, omega-k, RFI Suppression, Subaperture Processing, Digital Spotlighting, Slow-Time Upsampling, Alias-free Processing, Quadband SAR, P-Band, X-Band, L-Band, C-Band, Airborne SAR},
Pdf = {../../../docs/LeeVerdiSoumekh01.pdf}
}


9. F. Lombardini, F. Gini, and P. Matteucci. Application of array processing techniques to multibaseline InSAR for layover solution. In Radar Conference, 2001. Proceedings of the 2001 IEEE, pages 210-215, May 2001.
@InProceedings{Lombardini2001,
Title = {Application of array processing techniques to multibaseline InSAR for layover solution},
Author = {Lombardini, F. and Gini, F. and Matteucci, P.},
Booktitle = {Radar Conference, 2001. Proceedings of the 2001 IEEE},
Doi = {10.1109/NRC.2001.922979},
Month = may,
Pages = {210--215},
Year = {2001},
Owner = {ofrey}
}


10. F. Lombardini, F. Gini, and P. Matteucci. Multibaseline ATI-SAR for robust ocean surface velocity estimation in presence of bimodal Doppler spectrum. In Geoscience and Remote Sensing Symposium, 2001. IGARSS '01. IEEE 2001 International, volume 1, pages 578-580, July 2001.
@InProceedings{Lombardini2001a,
Title = {Multibaseline ATI-SAR for robust ocean surface velocity estimation in presence of bimodal Doppler spectrum},
Author = {Lombardini, F. and Gini, F. and Matteucci, P.},
Booktitle = {Geoscience and Remote Sensing Symposium, 2001. IGARSS '01. IEEE 2001 International},
Month = jul,
Pages = {578--580},
Volume = {1},
Year = {2001},
Owner = {ofrey}
}


11. Jordi J. Mallorqui, I. Rosado, and M. Bara. Interferometric calibration for DEM enhancing and system characterization in single pass SAR interferometry. In Proc. IEEE Int. Geosci. Remote Sens. Symp., volume 1, pages 404-406, July 2001.
@InProceedings{Mallorqui2001,
Title = {Interferometric calibration for DEM enhancing and system characterization in single pass SAR interferometry},
Author = {Mallorqui, Jordi J. and Rosado, I. and Bara, M.},
Booktitle = {Proc. IEEE Int. Geosci. Remote Sens. Symp.},
Month = jul,
Pages = {404-406},
Volume = {1},
Year = {2001},
Owner = {ofrey},
Timestamp = {2009.03.05}
}


12. Seung-Mok Oh and James H. McClellan. Multiresolution Imaging with Quadtree Backprojection. In The Record of the Thirty-Fifth Asilomar Conference on Signals, Systems and Computers, 2001, volume 1, pages 105-109, November 2001. Keyword(s): SAR Processing, Back-Projection, Time-Domain Back-Projection, TDBP, Quadtree Processing, Divide and Conquer Methods.
 Abstract: The quadtree backprojection is an efficient space-time synthetic aperture radar (SAR) imaging algorithm that is based on the spectral decomposition of SAR data. Normally the quadtree backprojection is represented as a multiple stage imaging process that performs the space-time domain imaging over a number of sub-patches separately at each stage. By representing the contents of each sub-patch with a predefined energy function, it is possible to form a sequence of multi-resolution images. In this paper, we discuss various applications where this quadtree imaging can be applied to provide the multiresolution imaging. These include SAR, tomographic medical imaging and beamforming.

@InProceedings{SeungMcClellan01:Backproj,
Title = {{Multiresolution Imaging with Quadtree Backprojection}},
Author = {Seung-Mok Oh and James H. McClellan},
Booktitle = {The Record of the Thirty-Fifth Asilomar Conference on Signals, Systems and Computers, 2001},
Month = Nov,
Pages = {105-109},
Volume = {1},
Year = {2001},
Abstract = {The quadtree backprojection is an efficient space-time synthetic aperture radar (SAR) imaging algorithm that is based on the spectral decomposition of SAR data. Normally the quadtree backprojection is represented as a multiple stage imaging process that performs the space-time domain imaging over a number of sub-patches separately at each stage. By representing the contents of each sub-patch with a predefined energy function, it is possible to form a sequence of multi-resolution images. In this paper, we discuss various applications where this quadtree imaging can be applied to provide the multiresolution imaging. These include SAR, tomographic medical imaging and beamforming.},
Keywords = {SAR Processing, Back-Projection,Time-Domain Back-Projection, TDBP, Quadtree Processing, Divide and Conquer Methods},
Pdf = {../../../docs/seungMcClellan01.pdf}
}


13. Tim Payne. Phase analysis for the limitations of the tomographic paradigm on a 3D scene. In Geoscience and Remote Sensing Symposium, 2001. IGARSS '01. IEEE 2001 International, volume 7, pages 3030-3032, 2001. Keyword(s): SAR Processing, SAR Tomography, Tomography, geophysical techniques, radar theory, remote sensing by radar, synthetic aperture radar, terrain mapping, 3D Fourier transform, 3D scene, SAR, complex surface reflectivity, demodulated pulses, geophysical measurement technique, land surface, phase analysis, phase errors, spotlight mode, synthetic aperture radar, terrain mapping, three dimensional scene.
 Abstract: The tomographic paradigm argues that the demodulated pulses from a spotlight mode SAR system trace a 2D slice of the 3D Fourier transform of the complex surface reflectivity. This paper derives the phase errors that result from imaging a 3D surface from a non planar collection geometry and shows how correct projection to the true surface can eliminate many of the errors. The response from an ideal scatterer is derived and then approximated to simplify the expression into a manageable and meaningful form and so that insight can be gained into the artifacts produced. The theory indicates that warping an image by distorting the final image to correct for layover doesn't eliminate the second order blurring terms produced by the relief and that both the layover and these blurring affects can be properly eliminated through correct projection to the real ground plane

@InProceedings{payne01:Tomo,
Title = {Phase analysis for the limitations of the tomographic paradigm on a 3D scene},
Author = {Payne, Tim},
Booktitle = {Geoscience and Remote Sensing Symposium, 2001. IGARSS '01. IEEE 2001 International},
Pages = {3030--3032},
Url = {http://ieeexplore.ieee.org/iel5/7695/21051/00978244.pdf},
Volume = {7},
Year = {2001},
Abstract = {The tomographic paradigm argues that the demodulated pulses from a spotlight mode SAR system trace a 2D slice of the 3D Fourier transform of the complex surface reflectivity. This paper derives the phase errors that result from imaging a 3D surface from a non planar collection geometry and shows how correct projection to the true surface can eliminate many of the errors. The response from an ideal scatterer is derived and then approximated to simplify the expression into a manageable and meaningful form and so that insight can be gained into the artifacts produced. The theory indicates that warping an image by distorting the final image to correct for layover doesn't eliminate the second order blurring terms produced by the relief and that both the layover and these blurring affects can be properly eliminated through correct projection to the real ground plane},
Keywords = {SAR Processing, SAR Tomography, Tomography, geophysical techniques, radar theory, remote sensing by radar, synthetic aperture radar, terrain mapping, 3D Fourier transform, 3D scene, SAR, complex surface reflectivity, demodulated pulses, geophysical measurement technique, land surface, phase analysis, phase errors, spotlight mode, synthetic aperture radar, terrain mapping, three dimensional scene},
Owner = {ofrey},
Pdf = {../../../docs/payneTomo01.pdf}
}


14. Mats I. Pettersson. Moving Target Detection in Wide Band SAR. In CIE International Conference on Radar, 2001, pages 614-618, October 2001. Keyword(s): SAR Processing, Back-Projection, Fast Back-Projection, Time-Domain Back-Projection, TDBP, Moving Target Indication, Ultra-Wideband SAR.
 Abstract: A likelihood ratio test is proposed for moving target detection in a ultra wide frequency band and wide antenna beam (wide band) SAR systems. The developed method combines time domain fast backprojection SAR processing methods with moving target detection. It saves the 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{Pettersson01:BackprojTarget,
Title = {{Moving Target Detection in Wide Band SAR}},
Booktitle = {CIE International Conference on Radar, 2001},
Month = Oct,
Pages = {614-618},
Year = {2001},
Abstract = {A likelihood ratio test is proposed for moving target detection in a ultra wide frequency band and wide antenna beam (wide band) SAR systems. The developed method combines time domain fast backprojection SAR processing methods with moving target detection. It saves the 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, Time-Domain Back-Projection, TDBP, Moving Target Indication, Ultra-Wideband SAR},
}


15. M. Preiss, D. Gray, and N.J.S. Stacy. The effect of polar format resampling on uncompensated motion phase errors and the phase gradient autofocus algorithm. In Geoscience and Remote Sensing Symposium, 2001. IGARSS '01. IEEE 2001 International, volume 3, pages 1442-1444, July 2001. Keyword(s): SAR Processing, Autofocus, Phase Gradient Autofocus.
@InProceedings{Preiss2001,
Title = {The effect of polar format resampling on uncompensated motion phase errors and the phase gradient autofocus algorithm},
Author = {Preiss, M. and Gray, D. and Stacy, N.J.S.},
Booktitle = {Geoscience and Remote Sensing Symposium, 2001. IGARSS '01. IEEE 2001 International},
Month = jul,
Pages = {1442--1444},
Volume = {3},
Year = {2001},
Keywords = {SAR Processing, Autofocus, Phase Gradient Autofocus},
Owner = {ofrey}
}


16. Lars M. H. Ulander, Per-Olov Frölind, A. Gustavsson, H. Hellsten, T. Jonsson, B. Larsson, and G. Stenstrom. Performance of the CARABAS-II VHF-Band Synthetic Aperture Radar. In IGARSS '01, International Geoscience and Remote Sensing Symposium, volume 1, pages 129 - 131, Jul. 2001. Keyword(s): SAR Processing, RFI Suppression, Back-Projection, Ultra-Wideband SAR, Time-Domain Back-Projection, TDBP, VHF SAR, CARABAS, Airborne SAR.
 Abstract: CARABAS-II is an airborne SAR operating in the 20-90 MHz band. The low operating frequency enables detection of concealed objects in dense forests as well as mapping of forest stem volume. A number of calibration experiments have recently been conducted to evaluate system performance. In this paper, we report on some of the results from the analysis. Spatial resolution, measured using 5-m trihedrals, is typically 2.5 m in both slant range and azimuth. The right-left ambiguity ratio, measured using 5-m trihedrals on both sides of the flight track, is about 10 dB for a single antenna element on receive. The noise level varies in the images and includes both multiplicative (integrated sidelobe ratio, right-left ambiguity ratio) and additive (radio-frequency interference, receiver noise) terms. Analysis of images from a recent campaign in northern Sweden shows that the additive noise term is less than -20 dB (noise-equivalent beta ?) for slant ranges less than 14 km.

@InProceedings{UlaFroGustHelJonLarsSten01:CARABAS,
Title = {{Performance of the CARABAS-II VHF-Band Synthetic Aperture Radar}},
Author = {Lars M. H. Ulander and Per-Olov Fr{\"o}lind and A. Gustavsson and H. Hellsten and T. Jonsson and B. Larsson and G. Stenstrom},
Booktitle = {IGARSS '01, International Geoscience and Remote Sensing Symposium},
Month = {Jul.},
Pages = {129 - 131},
Url = {http://ieeexplore.ieee.org/iel5/7695/21054/00976079.pdf},
Volume = {1},
Year = {2001},
Abstract = {CARABAS-II is an airborne SAR operating in the 20-90 MHz band. The low operating frequency enables detection of concealed objects in dense forests as well as mapping of forest stem volume. A number of calibration experiments have recently been conducted to evaluate system performance. In this paper, we report on some of the results from the analysis. Spatial resolution, measured using 5-m trihedrals, is typically 2.5 m in both slant range and azimuth. The right-left ambiguity ratio, measured using 5-m trihedrals on both sides of the flight track, is about 10 dB for a single antenna element on receive. The noise level varies in the images and includes both multiplicative (integrated sidelobe ratio, right-left ambiguity ratio) and additive (radio-frequency interference, receiver noise) terms. Analysis of images from a recent campaign in northern Sweden shows that the additive noise term is less than -20 dB (noise-equivalent beta ?) for slant ranges less than 14 km.},
Keywords = {SAR Processing, RFI Suppression, Back-Projection, Ultra-Wideband SAR, Time-Domain Back-Projection, TDBP, VHF SAR, CARABAS, Airborne SAR},
}


17. Lars M. H. Ulander, Hans Hellsten, and Gunnar Stenström. Performance analysis of fast backprojection for synthetic-aperture radar processing. In Edmund G. Zelnio, editor, Proc. of SPIE Vol. 4382, Algorithms for Synthetic Aperture Radar Imagery VIII, number 1, pages 13-21, 2001. SPIE. Keyword(s): SAR Processing, Back-Projection, Time-Domain Back-Projection, TDBP, Fast Back-Projection, inversion.
 Abstract: Exact SAR inversion for a linear aperture may be obtained using fast transform techniques. Alternatively, backprojection in time domain may be used which can also handle general curved apertures. In the past, however, backprojection has seldom been used due to its heavy computational burden. We show in the paper that the backprojection method can be formulated as an exact recursive method based on factorization of the aperture. By sampling the backprojected data in local polar coordinates it is shown that the number of operations is drastically reduced and can be made to approach that of fast transform algorithms.

@InProceedings{UlanderHellstenStenstroem2001,
author = {Lars M. H. Ulander and Hans Hellsten and Gunnar Stenstr{\"o}m},
title = {Performance analysis of fast backprojection for synthetic-aperture radar processing},
booktitle = {Proc. of SPIE Vol. 4382, Algorithms for Synthetic Aperture Radar Imagery VIII},
year = {2001},
editor = {Edmund G. Zelnio},
number = {1},
pages = {13-21},
publisher = {SPIE},
abstract = {Exact SAR inversion for a linear aperture may be obtained using fast transform techniques. Alternatively, backprojection in time domain may be used which can also handle general curved apertures. In the past, however, backprojection has seldom been used due to its heavy computational burden. We show in the paper that the backprojection method can be formulated as an exact recursive method based on factorization of the aperture. By sampling the backprojected data in local polar coordinates it is shown that the number of operations is drastically reduced and can be made to approach that of fast transform algorithms.},
file = {:UlanderHellstenStenstroem2001.pdf:PDF},
keywords = {SAR Processing, Back-Projection, Time-Domain Back-Projection, TDBP, Fast Back-Projection, inversion},
location = {Orlando, FL, USA},
owner = {ofrey},
pdf = {../../../docs/UlanderHellstenStenstroem2001.pdf},

}


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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.