Estimating aerodynamic resistance of rough surfaces using angular reflectance |
| |
Authors: | Adrian Chappell Scott Van Pelt Zhibao Dong |
| |
Affiliation: | a CSIRO Land and Water, GPO Box 1666, Canberra, ACT 2601, Australia b Agricultural Research Service, United States Department of Agriculture, Big Spring, TX, 79720, USA c Agricultural Research Service, United States Department of Agriculture, Lubbock, TX, 79720, USA d Key Laboratory of Desert and Desertification, Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences, No. 320 West Donggang Road, Lanzhou 730000, Gansu Province, PR China |
| |
Abstract: | Current wind erosion and dust emission models neglect the heterogeneous nature of surface roughness and its geometric anisotropic effect on aerodynamic resistance, and over-estimate the erodible area by assuming it is not covered by roughness elements. We address these shortfalls with a new model which estimates aerodynamic roughness length (z0) using angular reflectance of a rough surface. The new model is proportional to the frontal area index, directional, and represents the geometric anisotropy of z0. The model explained most of the variation in two sets of wind tunnel measurements of aerodynamic roughness lengths (z0). Field estimates of z0 for varying wind directions were similar to predictions made by the new model. The model was used to estimate the erodible area exposed to abrasion by saltating particles. Vertically integrated horizontal flux (Fh) was calculated using the area not covered by non-erodible hemispheres; the approach embodied in dust emission models. Under the same model conditions, Fh estimated using the new model was up to 85% smaller than that using the conventional area not covered. These Fh simulations imply that wind erosion and dust emission models without geometric anisotropic sheltering of the surface, may considerably over-estimate Fh and hence the amount of dust emission. The new model provides a straightforward method to estimate aerodynamic resistance with the potential to improve the accuracy of wind erosion and dust emission models, a measure that can be retrieved using bi-directional reflectance models from angular satellite sensors, and an alternative to notoriously unreliable field estimates of z0 and their extrapolations across landform scales. |
| |
Keywords: | Dust emission model Wind erosion Sheltering Erodible Flow separation Drag Wake Aerodynamic resistance Aerodynamic roughness length Shadow Illumination Ray-casting Digital elevation model Roughness density Frontal area index Angular reflectance Bi-directional reflectance |
本文献已被 ScienceDirect 等数据库收录! |
|