Spatio-temporal distribution of the zero-Doppler line of lunar-based SAR

Zero Doppler centroid imaging is of great significance in synthetic aperture radar interferometry (InSAR). Because the moon's orbit is elliptical and its orientation cannot be changed artificially, the zero Doppler centroid of lunar-based synthetic aperture radar (LB-SAR) is not steerable and will vary with lunar rotation and SAR system's position on lunar surface. Therefore, the distribution of zero Doppler centroid of LB-SAR will provide an important reference for observation model design of LB-SAR/InSAR. In this letter, we propose a calculation method of zero Doppler centroid by using the Jet Propulsion Laboratory (JPL)/NASA development ephemeris 430 (DE430), investigate the spatio-temporal distribution of the zero-Doppler line (ZDL). The results show that 1) the position of zero Doppler centroid deviates from the central meridian of a sublunar point from 0 degrees to 45 degrees within a sidereal month, 2) the maximum longitude difference of ZDLs corresponding to different SAR system's position on lunar surface is about 60 km, and 3) the greatest effect of topography on ZDL estimation is about 1.1 km. The proposed calculation method of ZDL and results analysis are of instructive significance to the site selection and attitude control of lunar-based radar in the design of LB-SAR/InSAR.