Sensitivity of radar backscatter to desert surface roughness

Abstract

Synthetic aperture radar (SAR) data have proved useful in remote sensing studies of deserts, enabling different surfaces to be discriminated by differences in roughness properties. Roughness is characterized in SAR backscatter models using the standard deviation of surface heights (σ), correlation length (L) and autocorrelation function (ρ(ξ)). Previous research has suggested that these parameters are of limited use for characterizing surface roughness, and are often unreliable due to the collection of too few roughness profiles, or under‐sampling in terms of resolution or profile length (Lp ). This paper reports on work aimed at establishing the effects of Lp and sampling resolution on SAR backscatter estimations and site discrimination. Results indicate significant relationships between the average roughness parameters and Lp , but large variability in roughness parameters prevents any clear understanding of these relationships. Integral equation model simulations demonstrate limited change with Lp and under‐estimate backscatter relative to SAR observations. However, modelled and observed backscatter conform in pattern and magnitude for C‐band systems but not for L‐band data. Variation in surface roughness alone does not explain variability in site discrimination. Other factors (possibly sub‐surface scattering) appear to play a significant role in controlling backscatter characteristics at lower frequencies.