基于数字高程模型，建立起伏地形的三维网格模型。利用坡角及坡向得到坡面像元的平均法向，通过坐标系转换，计算任一坡面在局部坐标系下对应的太阳入射及观测几何。在可见光及近红外波段，考虑遮蔽效应，建立裸露起伏地表的双向反射分布函数(BRDF)模型，并以沙漠地区为例验证了该模型的正确性。研究了沙漠地区地表起伏程度及太阳天顶角对BRDF 的影响，结果表明，在太阳几何一定的情况下，不同起伏地形的BRDF 随观测方位角的变化呈不对称分布，且近垂直主平面方向的BRDF 比近主平面方向整体偏大；对于同一地形，随着太阳天顶角增大，地表BRDF呈减小趋势。此外，随着波长增加，地表BRDF呈增大趋势。

A three-dimensional mesh model of rugged terrain is built based on the digital elevation model data. The average normal vector of each slope element is derived from its slope angle and aspect. Given the sun-view geometry in global system, the sun- view geometry of each slope element in local coordinate system can be calculated through coordinate conversion. Considering the shadowing effect, a bidirectional reflectance distribution function (BRDF) model of bare surface over rugged terrain is established in visible and near-infrared band. The validation of the model in desert area is conducted. The effect of the degree of surface relief and solar zenith angle on the model is studied. The results show that the tendency of BRDF varying with viewing azimuth angle of different rugged terrains has characteristic asymmetric distribution. BRDF in near perpendicular plane is larger than that in near principal plane. BRDF of the same rugged terrain decreases with the increase of solar zenith angle. BRDF tends to be larger as the wavelength increases.