Spatial and Temporal Behavior of Microwave Backscatter Directional Modulation Over the Saharan Ergs

Radar backscatter (sigmadeg) from ergs is modulated with view direction [incidence (thetas) and azimuth (phi) angles], where the modulation characteristics reflect the surface geometry. sigmadeg also varies spatially and reflects the spatial inhomogeneity of the sand surface. We use sigmadeg measurements at different thetas and phi angles from the NASA, European Remote Sensing satellite, and SeaWinds scatterometers to understand the relationship between wind and erg bedforms. A model incorporating the sigmadeg phi-modulation and spatial inhomogeneity is proposed. Surface slope variations are related to the sigmadeg 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 phi-modulation at thetas=33deg 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