LT-1A/B Satellite SAR Geometric Calibration and Absolute Location Error Analysis

LuTan-1 (LT-1) is China's first L-band differential interferometric synthetic aperture radar (SAR) satellite system, and also the first twin L-band SAR satellite system in the world. Geometric accuracy is one of the most crucial indicators for remote sensing satellites. SAR images with high geometric accuracy not only establish a more accurate geometric correspondence between image pixels and actual ground objects but also greatly simplify the later application. This article primarily explores the geometric error issues of the LT-1 satellite system, encompassing analysis of error sources, error modeling, and correction. Through research conducted on 232 acquisitions of LT-1 covering three calibration arrays across the globe during the in-orbit commissioning phase, it is shown that the direct out-of-box LT-1 SAR imagery exhibits a slant range deviation of approximately 38 m and an azimuth deviation of about 15 m. After applying the correction methods described in this article, the range accuracy is improved to 0.7 m, and the azimuth accuracy is enhanced to 2.1 m. In addition, we found that after correcting for atmospheric delay, there still exists a correlation between the slant range errors and beams. Optimal correction results can only be achieved through beam-wise calibration. Since the LT-1 operates in the L-band SAR frequency range, where ionospheric propagation delay is significant. We analyzed the relationship between ionospheric delay estimation error and slant range error. Our analysis revealed that the accuracy of ionospheric delay estimation is the primary factor limiting the precision of the slant range.