Estimation of land instantaneous photosynthetically active radiation over complex terrain based on MODIS porducts
MODIS产品估算复杂地形下的光合有效辐射

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.