Applications of spaceborne radar laboratory data to the study of aeolian processes

Aerodynamic roughness (z₀) is an important parameter in studies of sand and dust transport, as well as atmospheric circulation models. Aerodynamic roughness is a function of the size and spacing of surface roughness elements and is typically determined at point locations in the field from wind velocity profiles. Because field measurements require complex logistics, z₀ values have been obtained for very few localities. If radar can be used to map z₀, estimates can be obtained for large areas. In addition, because aerodynamic roughness can change in response to surface processes (e.g., flooding of alluvial surfaces), radar remote sensing could obtain new measurements on short timescales. Both z₀ and the radar backscatter coefficient σ⁰ are dependent on topographic roughness at the submeter scale, and correlation between these two parameters was developed based on radar data obtained from aircraft (AIRSAR). The Spaceborne Radar Laboratory (SRL) afforded the opportunity to test the correlation for data obtained from orbit. SRL data for sites in Death Valley, California; Lunar Lake, Nevada; and Gobabeb, Namibia, were correlated with wind data and compared with previous radar z₀ relations. Correlations between σ⁰ and z₀ for L band (λ=24cm) HV (H, vertically and V, vertically polarized modes) L band HH, and C band (λ=5.6cm) HV compare favorably with previous studies. Based on these results, maps of z₀ values were derived from SRL data for each site, demonstrating the potential to map z₀ for large vegetation-free areas from orbit using radar systems.