Geometric Correction of Bistatic SAR Moon Mapping Results Based on the RPC Model

Abstract

The bistatic synthetic aperture radar (SAR) system based on the Five-Hundred-Meter Aperture Spherical Radio Telescope (FAST) has successfully acquired multiple high-quality Moon surface images. However, the system errors introduced by noncooperative transmitting and receiving radars prevent traditional geometric correction methods based on geographic data and radar parameters from accurately transforming delay-Doppler format images into geographic coordinates, making it impossible to further utilize these images for scientific applications. In this letter, a novel geometric correction method is proposed for transforming delay-Doppler images to the Moon’s geographic coordinate images. This approach utilizes a geometric positioning model to generate ideal delay-Doppler coordinates corresponding to the Moon’s geographic coordinates. These coordinate pairs are used to fit the rational polynomial coefficient (RPC). Subsequently, based on the RPC model, localization offsets are corrected through an affine transformation and selective coefficient optimization. An optical-SAR image registration method is used to determine the localization offsets and evaluate the reliability of the geometric correction method. We demonstrate this approach using Moon SAR images obtained by the bistatic SAR system based on FAST and other transmitting radars. This method can effectively integrate multisource Moon SAR data to address specific scientific challenges.