MODIS-derived daily PAR simulation from cloud-free images and its validation

摘要: In this paper, a MODIS-derived daily PAR (photosynthetically active radiation) simulation model from cloud-free image over land surface has been developed based on Bird and Riordan's model. model, the total downwelling spectral irradiance is divided into two parts: one beam irradiance, another diffuse irradiance. The attenuation of solar comprises scattering by gas mixture, absorption ozone, mixture water vapor, aerosols. scattered out direct towards surface. multiple ground-air interactions have taken account in parameters needed are atmospheric vapor content, aerosol optical thickness albedo ranging 400 nm to 700 nm. They all retrieved MODIS data. Then, instantaneous photosynthetically available radiation (IPAR) integrated using weighted sum at each visible wavebands. Finally, derived integration IPAR. order validate we compared field measurements 2003 2004 against simulated PAR. were made Qianyanzhou ecological experimental station, Chinese Ecosystem Research Network. A 54 days L1B level images used for simulation. Our results show that consistent with measurements, where correlation coefficient linear regression between calculated measured 0.93396. However, there some uncertainties comparison 1 km pixel tower flux stand measurement. © 2007 Elsevier Ltd. All rights reserved.