Fully polarimetric scattering from random rough layers under the geometric optics approximation: Geoscience applications

Predictions of the geometric optics approximation for scattering from two rough interfaces that separate three homogeneous media (the “GO‐layer” model) are examined for their implications for radar remote sensing. A previous formulation of the rough layer normalized radar cross section (NRCS) is also extended to allow calculation of the polarimetric covariance of the scattered field. Example results are presented for both bistatic and monostatic configurations, and show the influence of subsurface interfaces on scattered field properties. In particular, complete hemispherical bistatic patterns of both NRCS and polarimetric correlations are illustrated to provide insight into the impact of subsurface layers on these quantities. It is shown that the observability of sub‐surface contributions in general is larger for geometries where upper interface returns are smaller (i.e. angles outside the quasi‐specular return of the upper interface), and it is also shown that significant decorrelations between polarizations can occur in the presence of sub‐surface layers. Variations of field properties with medium physical parameters (inner layer thickness and relative permittivity, upper and lower surface RMS slopes, radar frequency) are also shown. A problem that has received extensive previous interest (subsurface sensing in arid regions having an upper sand layer over a granite bedrock) is re‐examined for remote sensing at higher frequencies, and it is shown that subsurface contributions can impact backscattered NRCS returns even up to X‐band frequencies. The examples presented can be utilized to assess the potential detectability of sub‐surface layers for both monostatic radar observations and near specular observations (as in GNSS reflection observations of land surfaces).