Geometric position error analysis of airborne SAR and geometric calibration with platform motion constraints

Abstract

Airborne synthetic aperture radar (SAR) has the advantages of flexible scanning geometry and high spatial resolution compared with spaceborne SAR. However, the quality and positioning accuracy are affected by platform instability caused by air turbulence and other factors. In this paper, the sources of geometric positioning error in airborne SAR were analyzed, including platform position error, time delay error and tropospheric delay error. To improve the positioning quality of airborne SAR, an imaging parameters calibration model considering velocity constraints (IFP-VC) was proposed to rectify the orbit parameters and enable geometric calibration to improve the positioning accuracy. The proposed IFP-VC model was applied to improve the positioning accuracy of airborne SAR images acquired in Hainan and Rizhao, China. The IFP-VC model demonstrated good positioning performance when using measured ground control points (GCPs) in Hainan, achieving a positioning accuracy of 1.42 m. In Rizhao, the proposed IFP-VC model yielded a positioning accuracy of 7.16–12.71 m and 2.05–6 m higher than the slant range and time calibration model and the unconstrained model when using manually selected GCPs, respectively. The multiple images combination strategy was superior to the single image strategy, and the initial positioning accuracy of 930 m was improved from 14.50 m using a single image to 12.47 m using 5 images. When applying the imaging parameters calibration results to the images in different tracks, the positioning accuracy can be improved to 31 m compared with the initial positioning accuracy. The geometric calibration of airborne SAR images has the potential to enhance its applications in remote sensing mapping, land-use change monitoring and ground target detection.