I. Introduction
An important problem in electromagnetic-oriented sensing of both surface and underground targets is the evaluation and understanding of ground surface scattering behavior. Although many phenomenological studies for natural surfaces have been carried out within the RF remote sensing community on the inference of physical parameters (such as soil composition and moisture content) from the surfaces' polarimetric and spectral scattering signature, the emphasis of contemporary investigations has been primarily on applications related to airborne or spaceborne technologies; as such, the standard radar operational modality of interest is often confined to non-grazing observation angles while the operational frequency is at -band and above. Recently, there has been considerable interest in the development of ground-based mobile sensing platforms for standoff detection and identification of in-road and roadside threats [1]–[4]. In these low-to-ground systems, as the radiowave propagation paths defining the electromagnetic interactions between the radar transceiver and targets adhere to the ground, existing ground surface scattering models must be supplemented, or extended, to include low-grazing angle effects. Accordingly, a full-wave electromagnetic simulation approach is proposed in this work to estimate rough surface background clutter as relevant to performance prediction for the forward-looking imaging radar developed at the Army Research Laboratory (ARL).