建立适用于多类型植被场景的热辐射方向性模型是进行地表热辐射方向性研究的一种手段。利用真实植株几何及生理参数的统计平均值来刻画理念植株,并给定其空间分布特征,进行不同生长期植被冠层的描述。基于冠层双向孔隙率思想构建了冠层热辐射方向性3维模型,模型继承了孔隙率模型在计算冠层热辐射方向性上的简洁优势同时以几何光学的思想考虑了冠层空间异质性对冠层热辐射方向性的影响。以玉米冠层为例,进行了不同生长期玉米冠层热辐射方向亮温的模拟,通过与实地测量数据的比对表明,本文发展的模型能够较准确地模拟不同生长期玉米植被场景的方向亮温变化规律,模拟误差主要来自理念株的刻画误差、玉米叶片形状的近似以及忽略了多次散射贡献等3个方面。模型的构建方法对稀疏植被场景、浓密植被场景、多类型植被的混合场景均可适用,不同观测几何下的植被场景4组份面积比计算结果有望应用于复杂地表条件下地表返照率的研究。

Plant canopy temperature and soil temperature can be used to estimate canopy transpiration. The sensible heat flux and latent heat flux of the soil are crucial in predicting drought and estimating crop yield. In reality, land vegetation has multiple types with different shapes and spatial distributions; thus, a general model suitable for variety of vegetation types is important to investigate the thermal radiation directivity of the surface covered by vegetation. Based on the theory of bidirectional gap probability, a three-dimensional simulation model for hermal radiation directivity of a nouniform canopy was established in this study. The ideal plant given the special distribution was employed to form the canopy observation scene. The ideal plant is the basic unit for describing the observation scene, which possesses the statistical averages of the parameters of all the plants in the observed area. The multi-angle thermal infrared field data of different growth periods of a corn crop was used to verify the results of the simulation model proposed in this paper. Encouraging results have been obtained. The results show that the model can accurately simulate the change trend in the canopy temperature distribution with only a small deviation, which may be attributed to the following factors:(1) The deviation in the parameters used to establish the ideal plant affects the simulation result. (2) The roughness of the soil layer and the shape of the leaf are not considered in the process of simulation. (3) The model does not consider multiple scattering in the canopy body. Moreover, the quantity of the plants in the observation area is limited, and the spatial distribution of the plants differs to a certain extent from the statistical average used in the simulation. Given the parameters of the ideal plant and its spatial distribution, the model can calculate the area ratios of the four components in asparse vegetation scene, dense vegetation scene, and a mixed vegetation scene. The results combined with the Li-Strahlergeometric-optical model could be applied to the study of the surface albedo under complex surface conditions.