This paper examines various ways in which changes in ground reflectivity enhanced by using polarization diversity in millimeter-wave imaging radar can be used as an aid to guidance and navigation. The paper introduces the concept of a polarization scattering matrix and shows how the returns from a linearly polarized mirror scanned radar and an autonomous ground vehicle together can be exploited to provide novel ground images made at all polarizations. The paper introduces a number of polarization-sensitive calibration reflectors, including a novel modified Bruderhedral, which are used to quantify the polarization vector. It is shown that changes in the ground reflectivity of the radar images, as a function of polarization, can be used to classify the terrain in ways beyond that which can be achieved using static reflectivity contrast alone.