Azimuth modulation of backscatter from SeaWinds and ERS scatterometers over the Saharo-Arabian deserts

Saharo-Arabian deserts includes large expanses of sand dunes called ergs. These dunes are formed and constantly reshaped by prevailing winds. We use backscatter (σ⁰) measurements observed at various azimuth angles from SeaWinds scatterometer (QSCAT) and ERS scatterometer (ESCAT) to determine the σ⁰ azimuthal modulation over the sand dunes. A second order harmonic equation is used to model the σ⁰ measurements as a function of azimuth angle and provides similar results for both sensors. Images of the magnitudes of the model harmonics show many small-scale linear features corresponding to the large dune fields in the ergs. The images of the phases of the two harmonics are coherent with the large scale topography of the area. Most ergs exhibit isophase related to the general orientation of large- and small-scale features of the sand surface.