Using albedo to reformulate wind erosion modelling, mapping and monitoring

Adrian Chappell 1, Nicholas Webb2
1CSIRO, Canberra, ACT, Australia, 2USDA-ARS JER, Las Cruces, NM, USA

Wind erosion and dust emission models are required to assess the impacts of dust in the Earth
system. We describe a need in aeolian research to adequately represent the spatial variability and particularly the area average of the key aerodynamic properties which influence these models and our understanding of the processes. The models are underpinned by a geometric property (lateral cover; L) used to characterise the aerodynamic roughness (sheltered area or wakes) of the Earth's surface and calibrate the momentum it extracts from the wind. We reveal an error in the calculation of L and demonstrate that significant aerodynamic interactions between roughness elements and their sheltered areas have been omitted particularly under sparse surface roughness. We describe a solution which develops earlier work to establish a relation between sheltered area and the proportion of shadow over a given area; the inverse of direct beam directional hemispherical reflectance (black sky albedo; BSA). We show direct relations between BSA and wind tunnel measurements and thereby provide direct calibrations of key aerodynamic properties. We demonstrate how those properties can be retrieved from BSA from any platform (mast, aircraft, satellite). MODIS BSA across Australia is used to illustrate how areal estimates of aerodynamic properties improve wind erosion modelling, mapping and monitoring frequently in time (8 days) and space (500 m) across scales of variation (grain to landscape). We show that this approach provides new opportunities to investigate the dynamics of wind erosion in space and time and elucidate aeolian processes across scales.