Estimation of Land Photosynthetically Active Radiation in Clear Sky Using MODIS Atmosphere and Land Products

摘要

Photosynthetically active radiation (PAR) is an essential parameter in vegetation growth models and soil carbon sequestration models. A method has been developed by which instantaneous PAR can be calculated with high accuracy from Moderate Resolution Imaging Spectroradiometer (MODIS) atmosphere and land products. This method is based on a simplification of the general radiative transfer equation, which considers five major processes of attenuation of solar radiation: 1) Rayleigh scattering, 2) absorption by ozone and water vapor, 3) aerosol scattering, 4) multiple reflectance between surface and atmosphere, and 5) three terrain factors: slope and aspect, isotropic sky view factor, and additional radiation by neighboring reflectance. A comparison from 2006 of 108 retrieved results to filed measured PAR, and the R~2 of 0.855, in the Yucheng site of the Chinese Ecosystem Research Network (CERN) indicates that the computed results can adequately interpret actual PAR.