Pol-SAR Image Simulation of the Lunar Surface With Data Analysis of Chandrayaan-2 and Mini-RF

Dual-frequency synthetic aperture radar (DFSAR) onboard Chandrayaan-2 and Mini-RF onboard Lunar Reconnaissance Orbiter have acquired fully polarized and compact polarized SAR data of the lunar surface. However, there are few numerical simulations of lunar SAR images. Here, a fully polarized SAR images simulation method of lunar rough surfaces is presented. Scatterings from lunar surfaces are numerically simulated with the Kirchhoff approximation and small perturbation model. The Range Doppler algorithm is used to produce the SAR images. SAR images of lunar craters are simulated and compared with the DFSAR and Mini-RF data. The influence of co-polarization ratio
$\sigma _{\text{HH}}^0/\sigma _{\text{VV}}^0$
on its relative phase are analyzed and validated with simulation and data. The enhanced polarized scatterings from undulating topography is simulated and validated with Mini-RF data at S-band and optical image of the crater Galilei E. Due to small incidence angles and radar parallax, strong backscattering caused by rocks at the crater wall facing away from the radar occupies more pixels in range direction in DFSAR images than Mini-RF images. DFSAR dual-frequency images of Apollo 17 landing site are specifically analyzed with assistances of simulations, optical images and high-resolution digital terrain model. Dual-frequency SAR images from Chandrayaan-2 reveal different geologic units of lunar surface, which are invisible in optical images. In addition, the inversion of orientation angles is analyzed as well. The simulation and analysis in this paper will be helpful in lunar SAR data interpretation.