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

Radar backscatter (σ°) from ergs is modulated with view direction [incidence (θ) and azimuth (ɸ) 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 6 and 4 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° ɸ-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 ɸ-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. [ABSTRACT FROM AUTHOR]