双向反射模型反演沙地表粗糙度研究

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

由于沙地通常处在半干旱地区,在风蚀作用下表面结构特征会有所改变,同时,沙地表面粗糙度与组成成分的时间与空间变化也是研究风蚀模型所必须的输入信息。作为一种非接触的探测手段,遥感技术有助于实现对沙地表面粗糙程度在时空尺度上的研究。为了利用反射特性描述沙地表面结构特征,以人为模拟的粗糙沙地表面为研究对象,基于野外实测多角度高光谱反射信息,分析了沙地表面粗糙度变化对反射信息分布的影响,并且结合双向反射模型,试图利用模型参数反演粗糙度特征。通过研究发现,如果按照入射方向与沙地表面沙垄方向分类来看,与入射方向平行或者垂直均会对沙地表面反射分布特性有所改变。当沙垄方向与入射光方向垂直时,会使后向散射的反射峰值增加;而沙垄方向与入射光平行时,会使后向散射峰值向主平面两侧扩张。双向反射模型可以模拟沙地表面的反射特性,根据模型参数的变化也可以表示出沙地表面的粗糙度变化特性。这表明双向反射信息可以用于量化沙地表面结构特征,而且有助于了解结构特征对沙地光学特性的影响,也为研究颗粒介质固有光学特性以及反演沙地表面结构特征提供依据。

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.