Area Estimates of Wind Friction Velocity Derived from Net Radiometers and MODIS Albedo

Soil surface properties influence the resistance of soils to wind erosion through their effects on the aerodynamic roughness of the surface (z₀), the threshold friction velocity for particle entrainment (u_*t), and the supply of loose erodible material. The spectral reflectance of the soil surface, and its albedo, are influenced by the same soil properties. A relation between the surface albedo and its aerodynamic roughness has been established, enabling estimates of wind erosion to be obtained from available satellite data. Here we compare estimates of wind friction velocity derived from traditional methods (wind velocity profiles) with those derived from the albedo model, at two separate scales – bare soil patch (via net radiometers) and landscape (via MODIS 500m albedo datasets). Results suggest that estimates of u_* from wind velocity profiles are highly variable and therefore uncertain as they changes in response to wind speed, direction, turbulence scales, and heterogeneity of the surface roughness. Albedo-derived estimates of surface wind friction velocity at both scales have smaller uncertainty as they are integrative over the measurement area, in addition to resolving the partition of wind momentum between roughness elements and the soil surface. With albedo-derived area estimates of wind friction velocity at the soil surface, the accuracy of aeolian sediment transport estimates across scales is improved.