Synthetic Aperture Radar acquisitions in nadir (sounding) and side-looking imaging modes are planned for the International-Mars Ice Mapper (I-MIM) orbiter mission to accurately detect ice buried just below the Martian surface. In an effort to gain a comprehensive understanding of the ice detection capability of the I-MIM L-band polarimetric SAR, we developed a Nadir Scattering Radar Model (NRSM), and evaluated it in comparison to a previously implemented Side-looking Radar Scattering Model (SRSM). Together, these Radar Scattering Models (RSMs) permit a thorough evaluation of key radar performance metrics for given sets of radar parameters and Martian surface and shallow subsurface scenarios, and offer new insights into potential depths of detection of buried water ice on Mars.