Surface roughness and slope measurements using polarimetric SAR data

In this paper, the circular polarization coherence, ρ_RRLL , is investigated as a potential estimator of terrain surface roughness and small-scale slopes. The studies utilize microwave backscatter collected from 1) dielectric surfaces in an anechoic chamber and 2) a desert test site using P-, L-, and C-band NASA/JPL AIRSAR data. These experimental studies and supporting theory, indicate a sensitive decrease of |ρ_RRLL| with increasing surface roughness ks over a range 0 ⩽ ks ⩽ 1. For the present studies this decrease is caused largely by the depolarizing effects of small-scale surface slopes in the azimuth direction rather than by volume, or multiple scatter. For cases when the scatter is reflection symmetric, the value of |ρ_RRLL| depends on the surface roughness and on the local incidence angle. The dependence of |ρ_PRRLL| on the local incidence angle is supported by theory and experimental results. For these same scattering cases, however, |ρ_PRRLL| is independent of the surface dielectric constant. Estimation of the functional dependency of |ρ_PRRLL| versus ks, for a mid-range incidence angle, has been carried out using roughness estimates derived from an empirical model