本研究建立了一个反映植被辐射传输和几何光学特性的混合模型,以模拟半干旱地区天然草地的多波段反射率值。该模型引入一个几何相似性参数,用以描述植株冠层的几何形状对叶/枝角分布、阴影地面比例、冠层和地面各光学分量、冠层反射率和总反射率的影响。模型模拟值与研究区3个不同退化程度羊草草地的实测值较为吻合,而且退化程度越轻的草地,模拟效果也越好。对于中度退化草地,在高度与冠幅之比（chw）不变的情况下,当45°≤太阳天顶角sza≤75°时,不同几何形状植株的总反射率之间无显著差异;当0°≤sza〈45°或75°〈sza≤90°时，锥体与球体和柱体植株的总反射率之间有较显著差异；而球体和柱体植株的总反射率之间始终无显著差异。当chw由小到大变化时，以上结论基本不变。

The study established an integrated model combining radiative transfer and geometric optical properties in order to smi ulatemulti-spectral reflectance ofsemi-arid naturalgrassland. Themodel introduced a geometrical smi ilarity parameter, which describes the influences of plant crown shape on leaf/branch angle distribution frequencies, fraction of shadowed or illuminated canopy and background, canopy reflectance, and finally scene reflectance. The smi ulated results agreed with themeasured values in the threeLeymus chinense grasslandswith differentdegradation degree, and the lowerwas degradation degree, the betterwere smi ulated results. For themoderately degraded grasslands, ifplantcrown height-to-width ratio(chw) was invariant, when 45°≤solar zenith angle(sza)≤75°, no significantdifferences occurred in scene reflectance (R) for different plant crown shapes; and when 0°≤sza<45°or 75°