Geometric Auto-Calibration of SAR Images Utilizing Constraints of Symmetric Geometry

Synthetic aperture radar (SAR) has evolved into an essential Earth observation technique. Geometric quality is one of its most fundamental elements to ensure subsequent applications. Excellent localization accuracy requires comprehensive error compensation and calibration, while traditional calibration work is time-consuming and depends on the test sites. Besides, the available calibration test sites are scarce and unevenly distributed for certain SAR satellites. It is, hence, necessary to research how to make geometric calibration without ground control points (GCPs) for SAR. This study proposes a method utilizing the constraints of symmetric geometry that could cancel out plane error symmetrically and then calculates calibration constants combined with external digital elevation model (DEM). Experiments demonstrate that the calibration accuracy of the proposed way is approximately 0.3 m along range direction when all constraints are met, and the discrepancy between the proposed method and that using GCPs is analyzed. Generally, the method can achieve fast, labor-saving, and normalized calibration work for SAR images in the absence of available control data.