Final results of the efficient TerraSAR-X calibration method

Abstract

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 in-orbit operation of the entire SAR system can be ensured. The paper describes both the in-orbit calibration method for TerraSAR-X and dedicated activities performed during the commissioning phase as well as final results derived from all calibration procedures.

TerraSAR-X Antenna Calibration and Monitoring Based on a Precise Antenna Model

“…For verification purpose, several few representative beams were selected to verify the calibration approach. A description of the absolute radiometric calibration would exceed the content of this paper and the interested reader is referred to [7] and [9].…”

TerraSAR-X Calibration Results

“…the connection between the SAR data and the earth surface could be calibrated down to an accuracy of almost one magnitude better than the product specification with 2m. By this accurately calibrated TerraSAR-X system the impact of propagation effects on the range delay could be verified for the first time by a SAR system [4]. …”

“…Separating the absolute calibration factor according to the beam ID, i.e. as function of look angle, the gain-offset between different beams could be likewise verified by deployed reference targets with an accuracy less than +/-0.2dB [4]. Hence, absolute radiometric calibration of the whole TerraSAR-X system must be independent on both, the position of the targets deployed within the swath and the beam being operated.…”

Multimode Hybrid Geometric Calibration of Spaceborne SAR Considering Atmospheric Propagation Delay

“…The geometric accuracy of international advanced SAR satellites such as TerraSAR-X, ERS, ALOS-PALSAR, Sentinel-1A, and RADARSAT-2 is better than 10 m without control points after compensating for the two calibration parameters mentioned above [2][3][4][5][6][7][8][9][10]. The geometric accuracy of ENVISAT-ASAR is better than 0.6 pixels in range, and better than 8 pixels in azimuth after the division of atmospheric composition, Puyssegur integrated the influence of the amount of clouds and free electrons, and gave the calculation model for the atmospheric refractive index [14] …”

“…In Equation (2), the first term is the atmospheric delay caused by the hydrostatic effect (air pressure), the second term is the atmospheric delay caused by humidity (water vapor), the third term is the atmospheric delay caused by liquid (water droplets), and the fourth term is the ionospheric delay.…”