A Statistical Rule of the Stokes Parameters of Pol-SAR for Identifying Flat Surface in PSR

Finding a flat area is critical for choosing the landing site, especially in the permanently shadowed region (PSR) without reference of optical images. The digital elevation model (DEM) data are not enough to describe the complex lunar topography in the landing mission. High-resolution polarimetric synthetic aperture radar (pol-SAR) can acquire the polarized scattering map of lunar surface. In this letter, Chandrayaan-2 pol-SAR images of flat and rocky regions at non-PSR are selected with the assistance of optical image. The statistics of the Stokes parameters can tell the difference between flat and rocky surfaces. Enhanced backscattering with a large variance from rough surfaces with rocks can be distinguished from the smooth and flat areas. Large value of the first Stokes parameter $I_{1}$ with extendedly distributed probability distribution function is related with the scatterings from rough surface and rocks. A statistics rule of the Stokes parameters is established and is applied to identify the flat regions in the PSR of the crater Shoemaker.