An Autofocus Approach for Residual motion errors with applications to airborne repeat-pass SAR interferometry (original) (raw)
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IEEE Transactions on Geoscience and Remote Sensing, 2000
Airborne repeat-pass SAR systems are very sensible to subwavelength deviations from the reference track. To enable repeat-pass interferometry, a high-precision navigation system is needed. Due to the limit of accuracy of such systems, deviations in the order of centimeters remain between the real track and the processed one, causing mainly undesirable phase undulations and misregistration in the interferograms, referred to as residual motion errors. Up to now, only interferometric approaches, as multisquint, are used to compensate for such residual errors. In this paper, we present for the first time the use of the autofocus technique for residual motion errors in the repeat-pass interferometric context. A very robust autofocus technique has to be used to cope with the demands of the repeat-pass applications. We propose a new robust autofocus algorithm based on the weighted least squares phase estimation and the phase curvature autofocus (PCA) extended to the range-dependent case. We call this new algorithm weighted PCA. Different from multisquint, the autofocus approach has the advantage of being able to estimate motion deviations independently, leading to better focused data and correct impulse-response positioning. As a consequence, better coherence and interferometric-phase accuracy are achieved. Repeat-pass interferometry based only on image processing gains in robustness and reliability, since its performance does not deteriorate with time decorrelation and no assumptions need to be made on the interferometric phase. Repeat-pass data of the E-SAR system of the German Aerospace Center (DLR) are used to demonstrate the performance of the proposed approach.
An Autofocus Approach for Residual Motion Errors With Application to Airborne
2008
Airborne repeat-pass SAR systems are very sensible to subwavelength deviations from the reference track. To enable repeat-pass interferometry, a high-precision navigation system is needed. Due to the limit of accuracy of such systems, deviations in the order of centimeters remain between the real track and the processed one, causing mainly undesirable phase undulations and misregistration in the interferograms, referred to as residual motion errors. Up to now, only interferometric approaches, as multisquint, are used to compensate for such residual errors. In this paper, we present for the first time the use of the autofocus technique for residual motion errors in the repeat-pass interferometric context. A very robust autofocus technique has to be used to cope with the demands of the repeat-pass applications. We propose a new robust autofocus algorithm based on the weighted least squares phase estimation and the phase curvature autofocus (PCA) extended to the range-dependent case. We call this new algorithm weighted PCA. Different from multisquint, the autofocus approach has the advantage of being able to estimate motion deviations independently, leading to better focused data and correct impulse-response positioning. As a consequence, better coherence and interferometric-phase accuracy are achieved. Repeat-pass interferometry based only on image processing gains in robustness and reliability, since its performance does not deteriorate with time decorrelation and no assumptions need to be made on the interferometric phase. Repeat-pass data of the E-SAR system of the German Aerospace Center (DLR) are used to demonstrate the performance of the proposed approach.
2008
Airborne SAR systems are traditionally considered to be a suitable testbed for the demonstration of new Earth observation data acquisition techniques and for the development of new applications based on the acquired multi parameter data sets. Spaceborne SAR system concepts and mission design is based on the experience gathered from these airborne SAR experiments and from dedicated campaigns. DLR's E-SAR system is supporting these activities since the late 1980-ties by providing high resolution multi-frequency and multi-polarisation data sets to a large user community. Triggered by the scientific needs and also by the recent advancements in motion compensation techniques several new operating modes are now available for the E-SAR system on a quasi-operational basis. This paper gives an overview of these techniques and presents novel application examples.
Trajectory Uncertainty in Repeat-Pass SAR Interferometry: A Case Study
IGARSS 2019 - 2019 IEEE International Geoscience and Remote Sensing Symposium, 2019
In the context of differential synthetic aperture radar interferometry (DInSAR), precise trajectory estimation of the SAR platform is necessary to minimize residual phase errors induced by inaccurate knowledge of the 3D acquisition geometry. Inertial navigation systems (INS) and global navigation satellite system (GNSS) are usually employed to track the position of the platform. However, their unavoidable inaccuracies lead to motion estimation errors that negatively affect the quality of the processed radar data. To assess the positioning performance in a repeat-pass scenario, we used a navigation-grade INS/GNSS system to precisely track the position and the attitude of a platform moving along a rail and carrying a SAR sensor. We analyse the performance of the positioning solution for different scenarios relevant to repeat-pass DInSAR. Since the position of the platform is nearly perfectly repeated at every pass (zero interferometric baseline), the precision of the estimated position can be assessed and the interferometric performance evaluated.
Precise Topography- and Aperture-Dependent Motion Compensation for Airborne SAR
IEEE Geoscience and Remote Sensing Letters, 2005
Efficient synthetic aperture radar (SAR) processing algorithms are unable to exactly implement the aperture-and topography-dependent motion compensation due to the superposition of the synthetic apertures of several targets having different motion errors and potentially different topographic heights. Thus, during motion compensation, a reference level is assumed, resulting in residual phase errors that impact the focusing, geometric fidelity, and phase accuracy of the processed SAR images. This letter proposes a new short fast Fourier transform-based postprocessing methodology capable of efficient and precise compensation of these topography-and aperture-dependent residual phase errors. In addition to wide beamwidth (very high resolution) SAR systems, airborne repeat-pass interferometry especially benefits from this approach, as motion compensation can be significantly improved, especially in areas with high topographic changes. Repeat-pass interferometric data of the E-SAR system of the German Aerospace Center (DLR) are used to demonstrate the performance of the proposed approach.
Advances in airborne SAR interferometry using the experimental SAR system of DLR
2007
During recent years the Experimental SAR (E-SAR) system of the German Aerospace Center (DLR) has continuously been operated to acquire data for different scientific applications in forestry, agriculture and glaciology. In this context, the data where mainly used to develop new scattering models in preparation of future space-borne missions posing increasing accuracy requirements especially for the processing of repeatpass interferometric data. Also direct model-free methods like differential SAR interferometry for measuring displacements in the order of the wavelength or SAR tomography for real 3D microwave imaging of scattering volumes determined the development of advanced and very accurate motion compensation techniques. This paper first gives an overview of the updates of the E-SAR system performed during the last couple of years and then focusses on the recently developed airborne interferometric processing methods and their applications.
Estimation of uncompensated trajectory deviations and image refocusing for high-resolution SAR
2015 German Microwave Conference, 2015
The accuracy of trajectory measurements is one of the crucial factors in high-resolution SAR imaging. Common navigation systems often do not fulfill the requirements that results in significant image quality degradation. In the paper, a new autofocus algorithm for the reconstruction of the SAR platform trajectory deviations is proposed. The approach is based on the estimation of the Doppler rate errors on a sequence of short-time intervals. The method is capable of estimation of time-varying and range-dependent phase error functions. The key steps of the developed technique are illustrated. The method is demonstrated on experimental data obtained with an X-band airborne SAR system.
1999
This paper presents first the relevant parameters of the experimental E-SAR system for single-and repeat-pass SAR interferometry. The implementation of the different interferometric operation modes is described and special attention is paid to the problems posed by the unstable airborne platform. Each interferometric mode is described including the solution of its critical problems. The given examples prove the enormous information content one can obtain from the different imaging modes of airborne SAR interferometry. Finally, future developments concerning polarimetric SAR interferometry and tomography will be addressed.
System Concepts for Bi and Multi-Static SAR Missions
The performance and capabilities of bi-and multistatic spaceborne synthetic aperture radar (SAR) are analyzed. Such systems can be optimized for a broad range of applications like frequent monitoring, wide swath imaging, single-pass cross-track interferometry, along-track interferometry, resolution enhancement or radar tomography. Further potentials arises from digital beamforming on receive, which allows to gather additional information about the direction of the scattered radar echoes. This directional information can be used to suppress interferences, to improve geometric and radiometric resolution, or to increase the unambiguous swath width. Furthermore, a coherent combination of multiple receiver signals will allow for a suppression of azimuth ambiguities. For this, a reconstruction algorithm is derived, which enables a recovery of the unambiguous Doppler spectrum also in case of non-optimum receiver aperture displacements leading to a non-uniform sampling of the SAR signal. This algorithm has also a great potential for systems relying on the displaced phase center (DPC) technique, like the high resolution wide swath (HRWS) SAR or the split antenna approach in the TerraSAR-X and Radarsat II satellites.
Multi-Satellite Interferometric SAR System
Proceedings of the Fifth International Conference on Telecommunications and Remote Sensing, 2016
In the present work a multi-satellite SAR system is considered. Between every pair of SAR satellites an interferometric concept is implemented. It allows the height of each pixel on the surface to be evaluated with high precision and a three dimensional map to be created. InSAR geometry is analytically described. Mathematical expressions for determination of current distances between SAR's and detached pixels on the ground, and principal InSAR parameters are derived. A model of linear frequency modulated (LFM) SAR signal with InSAR applications, reflected from the surface is developed. Correlation and spectral SAR image reconstruction algorithms and co-registration procedure are described. To verify the correctness of the signal model and image reconstruction and co-registration algorithm numerical experiment is carried out.