提出基于MODIS大气和地表产品反演高精度复杂地形下的光合有效辐射模型。该方法是对普通的大气传输模型进行简化, 在模型中分别考虑了削减光合有效辐射的5个主要因子: 瑞利散射、臭氧和水汽吸收、气溶胶散射以及地表和大气间的多次反射。从3个方面考虑了复杂地形对于光合有效辐射的影响: (1) 坡度和坡向; (2) 天空可视角; (3) 邻近地形的附加辐射。提取2006年晴空条件下的估算结果与中国生态网络山东禹城站和长白山站的实测值的比较, 得到相关系数分别为0.924和0.9, 表明模型反演结果能够较好地解译实际光合有效辐射的变化。通过比较考虑地形和不考虑地形2种情况得到的光合有效辐射, 定量地分析了地形对光合有效辐射的影响。
Photosynthetically Active Radiation (PAR) is an important parameter in models of ecosystem dynamics and carbon cycle. A method is presented with which instantaneous PAR can be calculated with high accuracy from Moderate Resolution Imaging Spectroradiometer (MODIS) products and Digital Elevation Model (DEM). The method is based on a simplification of the general radiative transfer equations, which considers five major processes of attenuation of solar radiation: Rayleigh scattering, absorption by ozone and water vapor, aerosol scattering, multiply reflectance between land surface and atmosphere, and three terrain factors: slope and aspect, isotropic sky view factor and additional radiation by neighbor reflectance. Comparing the modeling PAR with observational PAR in Yucheng site and Changbai Mountain site in 2006, the correlation coefficient are 0.929 and 0.904 respectively, and the average errors are 10% and 15% respectively, which should be sufficiently accurate for re-flecting the change of PAR. Comparing modeling PAR with the consideration of complex terrain with modeling PAR without the consideration of terrain, this paper quantificationally analyzes the effect of complex terrain.