TerraSAR-X Calibration Results

TerraSAR-X is a satellite mission for scientific and commercial applications operating a highly flexible X-band SAR instrument with a multitude of different operation modes. As product quality is of crucial importance, the success or failure of the mission depends essentially on the method of calibrating TerraSAR-X in an efficient way during commissioning the entire system in a restricted time. Only then, product quality and the correct operation of the SAR system can be ensured. The paper describes the method of calibrating TerraSAR-X and final results derived from all calibration procedures. 1 Scope and Strategy On June 15th, 2007, the first German SAR satellite for commercial and scientific applications, TerraSAR-X, was launched. The essential task of calibrating TerraSAR-X is to estimate and correct systematic error contributions throughout the complete SAR system and to tie-down im-age information (magnitude and phase) to reference units in geophysical terms. In addition to the high degree of flexibility of TerraSAR-X with different operation modes (StripMap, Spotlight, ScanSAR, right/left looking, etc.) and a tight performance with an absolute radiometric ac-curacy better than 1dB, the main goal after launch of the satellite is to provide calibrated and verified SAR data products as soon as possible. Thus, a strategy for an ef-ficient but robust calibration method was developed [1]. Applying a novel antenna model approach the in-orbit cali-bration method can be sub-divided into six major tasks per-formed during commissioning of TerraSAR-X. The suc-cessive baseline calibration procedures are: 1. Geometric Calibration, to assign the SAR data to the geographic location on the earth’s surface. 2. Antenna Pointing Determination, to obtain a cor-rect beam pointing of the antenna. 3. Antenna Model Verification, to ensure the provi-sion of the antenna patterns of all operation modes and the gain offset between different beams. 4. Relative Radiometric Calibration, for radiometric correction of SAR data within an illuminated scene