Precise Three-Dimensional Stereo Localization of Corner Reflectors and Persistent Scatterers With TerraSAR-X

This paper reports on the absolute 3-D localization of radar corner reflectors and persistent scatterers (PSs) by stereo synthetic aperture radar (SAR) carried out with TerraSAR-X and TanDEM-X. The novel combination of rigorously linearized range-Doppler equations with thorough sensor modeling, consideration of atmospheric delays, geodynamic signals, satellite dynamics, and geometrical calibration allows a direct target localization at the centimeter level. Therefore, there is no need for the application of geocoding since our approach delivers 3-D positions directly in the International Terrestrial Reference Frame (ITRF) 2008. Four radar corner reflectors located at the Wettzell Geodetic Observatory, Metsahovi Geodetic Observatory, and German Antarctic Receiving Station O'Higgins were localized in 3-D with a precision better than 4 cm. By introducing an updated geometrical calibration of TerraSAR-X and TanDEM-X, the absolute accuracy of the same level becomes possible, which was demonstrated by externally validating the reflector positions at Metsahovi and Wettzell against results of terrestrial geodetic surveying. Furthermore, PSs located in Berlin were retrieved with a precision of 10 cm, making the method a suitable tool for radar positioning in urban environments. Potential fields of application for our approach are the joint analysis with phase-based methods, geometrical calibration of radar satellites, and direct integration of SAR observations into Global Navigation Satellite System networks.