|Title||Using albedo to reform wind erosion modelling, mapping and monitoring|
|Publication Type||Journal Article|
|Year of Publication||2016|
|Authors||Webb N, Chappell A|
|ARIS Log Number||336635|
Dust emission models are used to assess the impacts of dust on radiative forcing in the atmosphere, cloud formation, nutrient fertilisation and human health. 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 two-dimensional geometric property (lateral cover; L) used to characterise the three-dimensional aerodynamic roughness (sheltered area or wakes) of the Earth’s surface and calibrate the momentum it extracts from the wind. We reveal a fundamental weakness in L and its latent influence on roughness configuration and demonstrate that significant aerodynamic interactions between roughness elements and their sheltered areas have been omitted particularly under sparse surface roughness (0.001<L<0.1). 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 shadow and wind tunnel measurements and thereby provide direct calibrations of key aerodynamic properties. Estimation of the aerodynamic parameters from albedo enables wind erosion assessments over areas across platforms from the field to airborne and readily available data from satellite remote sensing. The approach also demonstrated redundancy in existing wind erosion models and thereby reduced their complexity but improved fidelity. We found that the use of albedo enabled an adequate description of aerodynamic sheltering to characterise drag partition and predict sediment transport without the use of a drag partition scheme and the entrainment threshold. We applied the calibrations to produce global maps of aerodynamic properties which showed very similar spatial patterns to each other and confirmed the redundancy in the traditional approach to wind erosion modelling. The global maps identified regions of small aerodynamic roughness previously thought to be susceptible to wind erosion because of their erodibility. We evaluated temporal patterns of predicted horizontal mass flux at locations across Australia which revealed variation between land cover types that would not be detected using traditional models. The work shows how this new approach provides new opportunities to investigate the dynamics of wind erosion in space and time and elucidate aeolian processes across scales.