Estimation of Land Photosynthetically Active Radiation in Clear Sky Using MODIS
基于MODIS数据估算晴空陆地光合有效辐射

Photosynthetically active radiation (PAR) is a key variable required by almost all terrestrial ecosystem models. Unfortunately, the current incident PAR products estimated from remotely sensed data at spatial and temporal resolutions are not sufficient for carbon cycle modeling. In this paper, a method was proposed to retrieve land surface PAR from MODIS data in non-cloudy sky. Firstly, the maximum PAR in top of atmosphere was calculated in any place and at any time. Then the atmospheric parameters, vapor and aerosol, were estimated from MODIS data. Finally, the land surface PAR was computed by radiative transfer model using atmospheric parameters and sun geometrical information. The method was used to retrieve PAR in Shandong and the result was tested by the ground data in Yuncheng station of CERN with the error less than 10%.