Analysis of scatterometer observations of Saharan ergs using a simple rough facet model

The Sahara desert includes large expanses of sand dunes called ergs. These dunes are formed and constantly reshaped by prevailing winds. Previous study shows that Saharan ergs exhibit significant radar backscatter (sigmadeg) modulation with azimuth angle (Phi). We use sigmadeg measurements observed at various incidence angles (thetas) and Phi from the NASA scatterometer (NSCAT), the Seawinds scatterometer aboard QuikSCAT (QS-CAT), the ERS scatterometer (ESCAT) and the Tropical Rain Monitoring Mission´s Precipitation Radar (TRMM-PR) to model the sigmadeg response from sand dunes. Sand dunes are modeled as a composite of tilted rough facets and small ripples. The dune fields are modeled as composed of many simple dunes. The sigmadeg measured by the scatterometer from (thetas, Phi) look direction is the sum of the returns from all the rough facets in the footprint. The model is applied to linear and transverse dunes with rough facets and Gaussian tilt distributions. The model results in a sigmadeg response similar to the NSCAT and ESCAT observations over areas of known dune types in the Sahara. This analysis gives a unique insight into scattering by large scale sand bedforms