利用辐射度模型模拟玉米冠层辐射分布

Reflectance Distribution of Corn Canopies Simulated with Radiosity-graphics Combined Model

随着遥感研究的深入和计算机技术的提高,地面目标二向性反射分布函数(BRDF)的研究不断深入,计算机模拟模型因其对植被结构的细致描述并能更真实模拟光线与植被冠层之间的相互作用,受到越来越多的学者重视。本文以2000年在中国科学院栾城生态系统试验站测量的夏玉米为例,在对玉米三维结构进行实地测量的基础上,利用扩展的L系统对生长期的玉米进行建模,进而应用基于真实结构场景的辐射度模型(RGM)计算了玉米场景的二向性反射率因子(BRF),对模拟结果与实测结果进行了分析与比较,结果显示两者之间具有较好的一致性。证明辐射度模型用于植被冠层光辐射分布模拟是行之有效的,可以为波谱库提供可靠的多角度数据,并为进一步冠层辐射分布的研究工作奠定了基础。

In the research of quantitative remote sensing, bidirectional reflectance distribution function （BRDF） of the earth surface are important to understand the course and mechanism of the interaction between light and vegetation. According to the principles of the BRDF models, physical models of vegetation in the field of remote sensing can be divided into three categories： geometry optical models （GO）, radiance transfer models （RT） and computer simulation model. The computer simulation models, for instance, Monte Carlo, ray-tracing and radiosity, are paid more attention with the development of computer technology. The radiosity method is a powerful tool to describe the reflectance distribution from the canopies, which can take much more detailed structures of vegetations and the course of reflectance, transmittance and multiple-reflectance between the components in the scenes into account and help to understand and simulate the radiation distribution of canopies. In this study, summer corn was selected as an example and light distributions in the canopy were simulated with RGM （radiosity-graphics combined model）. First, three dimensional structures of corns were rendered with the modified extended L-systems （MELS） method using the statistical parameters measured in the field at Luancheng ecosystem station of Chinese Academy of Science, located in Hebei Province in 2000 （Longitude： 37°52′ N, latitude： 114°39′ E, altitude： 50.5 m） . Second, RGM, which can take much more detailed structures of vegetation canopies into account, was analyzed and applied to simulate the radiance distribution in the corn canopy. Finally, results of BRF simulated by RGM model were compared with those measured data in the field. They were both agreed well. Therefore, BRF simulated by the model can be used to supply the spectrum database or to supplement measured data. The intermediate result of simulation can also be use to analyze APAR in the canopy as well.