Surface Statistics of the Saharan Ergs observed in the σ Azimuth Modulation

Saharo-Arabian deserts 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 backscatter (σ) azimuth angle (φ) modulation. The phases of the modeled σ versus φ harmonics over the ergs are correlated to the orientation of the dune fields. Most of the vertical variation in ergs has low frequencies due to dunes (>100m) while high frequency variation is due to centimeter scale surface ripples. Although large scale features may be aperiodic, the small scale features are periodic and rapidly respond to changes in the prevailing wind which change their orientation and wavelength. In this paper, we use σ measurements from ERS scatterometer (ESCAT) and NASA scatterometer (NSCAT) to determine the surface profile statistics of the sand dunes. The total backscattering coefficient σ T from the sand as a function of incidence angle (θ) and φ is modeled as a sum is the contributions from surface scattering, subsurface volume scattering and subsurface bedrock scattering. The σ variations with the θ for different φ directions are observed.