Desert; European Centre for Medium-Range Weather Forecasts (ECMWF); European RemoteSensing Satellite Scatterometer (ESCAT); NASA Scatterometer (NSCAT); SeaWinds Scatterometer; dunes; ergs; winds;
Radar backscatter (σ˚) from ergs is modulated with view direction [incidence (θ) and azimuth (φ) angles], where the modulation characteristics reflect the surface geometry. σ˚ also varies spatially and reflects the spatial inhomogeneity of the sand surface. We use σ˚ measurements at different θ and φ angles from the NASA, European Remote Sensing satellite, and SeaWinds scatterometers to understand the relationship between wind and erg bedforms. A model incorporating the σ˚ φ-modulation and spatial inhomogeneity is proposed. Surface slope variations are related to the σ˚ spatial inhomogeneity. We compare the backscatter model results with numerically predicted wind direction data provided by the European Centre for Medium-Range Weather Forecasts (ECMWF) over the erg surfaces. We use the maxima of the φ-modulation at θ=33˚ to infer the orientation of the dominant slip-sides on the sand surface. These orientations are consistent with the ECMWF wind directions spatially and temporally.
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