[Study of Retrieving the Sandy Surface Roughness Land Based on the Bidirectional Reflectance Model]

In the semiarid area, the structural nature of sandy land is changed due to wind erosion. Furthermore, assessing the changes in the composition and surface roughness in several spatial and temporal scales is significant for the wind erosion model calculations. As a noninvasive approach, remote sensing can be used to improve the study of sandy surface in time and space. In order to characterize the surface structure using the reflectance of sandy land, we analysis the effects of the changes of sandy surface structure on the bidirectional reflectance distribution basing on the multi-angular and hyperspectral measurements in the field; the measured sandy land samples are taken from nature, but the surface structures are artificial: one type is the direction of sand furrows is parallel to the incident direction, the other is the direction of sand furrows is perpendicular to the incident direction. At the same time, we analyzed the effects of surface structure on the bidirectional reflectance factor of sand land and we also retrieve the sandy surface roughness using the reflectance model parameter. The results suggest that both types of sand furrows will influence the distribution of reflectance of sandy land surface, for example, the backward scattering of sandy land increased when the direction of sand furrows is perpendicular to the incident direction, and the range of backward scattering of sandy land expended when the direction of sand furrows is parallel to the incident direction. When we compared the measured reflectance with the modeled results basing on the reflectance model, it is found that the reflectance model can be used to simulate the reflectance property of sandy land surface and prove that the parameter of model is useful for retrieving the surface roughness. This research not only presents the sample for quantifying the structural information of sandy land by the reflectance measurements, but also shows valuable reference for the research of intrinsic optical property of sandy land and the reversion of the texture of sandy land. In other words, this paper can also help the scientists understand the effect of the structural information on the optical properties of sandy land.