Geodetic Stereo SAR - 4-D coordinate retrival of persistent scatterers from TerraSAR-X radar observations

Abstract

The combination of geodetic principles for correcting radio signals with spaceborne Synthetic Aperture Radar (SAR) has led to a new type of accurate radar observations. This approach is comparable to satellite altimetry or Global Navigation Satellite Systems (GNSS), where errors in the signal time-of-flight caused by the Earth’s atmosphere and the geodynamic effects (solid Earth tides, ocean loading, …) are removed by external models or complementary observations. In case of the radar satellites TerraSAR-X and TanDEM-X, the possibility of such geodetic SAR observations was demonstrated by using several radar corner reflectors with known reference coordinates. Their positions were retrieved not only in the 2-D radar geometry (range, azimuth) but also in absolute 3-D with an accuracy of 1-2 centimeter (1 sigma level). Moreover, additional velocity determination has become possible if the radar data has sufficient temporal coverage. After the successful demonstration for radar corner reflectors, the concept of geodetic stereo SAR shall now be applied to opportunistic persistent scatterers (PS) found in SAR images acquired in urban areas. TerraSAR-X data covering several years are available for the city of Munich and our general aim is the usage of geodetic stereo SAR to retrieve both the global coordinates of the PS as well as their common velocity vector linked to plate tectonics. Like in the case of the corner reflectors, a controlled test scenario has been established by selecting a building of Technische Universtät München (TUM) which provides a large set of PS clearly visible in the radar images. A detailed and geometrically accurate model of this building was created in the global reference frame, and analysed by ray tracing methods to verify the 3-D PS positions obtained from SAR. Regarding the secular velocity, permanent GNSS operated at TUM campus enables a reliable cross-comparison with the SAR-based solution. Our presentation gives insight into the methods and the results achieved for the TUM test scenario. In future, geodetic stereo SAR shall enable the straight forward integration of SAR observations into GNSS networks and support the observation of secular deformations like plate tectonics or post glacial rebound.