Influence of surface roughness frequency components of radar backscattering: consequences on roughness sampling

Natural soil surfaces present multiple, random roughness scales (or frequency components). Proper estimation of the correlation length, L, of a low frequency (LF) roughness component (typically L > 20 cm) requires excessively long profiles (>10 m). Consequently, usually applied sampling protocols were not suitable for an accurate determination of L. The objective of the study was to establish to which extent the low frequency component has a significant impact on the soil microwave backscattering. We implemented a model based on the Method of Moments (MM) to generate profiles presenting arbitrarily chosen multiple random roughness scales. It is shown that for angle of incidence lower than 40°, adding a low frequency component with a component greater than 4 times th e wave length does not affect the MM results. If profiles of 2 meters are used, we obtained much better results when the low frequency is removed.