MODIS-derived global products of solar radiation, photosynthetically active radiation, and diffuse photosynthetically active radiation at 5 km resolution from 2001 to 2014

Abstract:

Land surface remote sensing communities need high resolution solar radiation maps (1-5 km) in the global terrestrial ecosystems over a decadal period to better estimate carbon and water fluxes across different spatiotemporal scales. In spite of the significance of solar radiation in land surface processes, there have been surprisingly little efforts to develop high resolution solar radiation maps globally, which hindered scaling-up plot level intensive observations on the land surface processes into regional, continental, and global scales. Here, we report MODIS-derived solar radiation (Rg), photosynthetically active radiation (PAR), and diffuse PAR (dPAR) products over the global land between 2001 and 2014 at 5 km resolution with 4 day intervals. We used MODIS Atmosphere and Land products as inputs to an atmospheric radiative transfer model which computed Rg, PAR and dPAR under all sky conditions. We scaled up instantaneous estimates of the radiation components to the daily sum, and 4 daily mean sum estimates using a simple sinusoidal function. To evaluate Rg, PAR and dPAR products, we used ~80 station data collected in BSRN, FLUXNET and Ameriflux networks which cover a range of climatic zones from the arctic to tropical zones. The computed Rg, PAR, and dPAR products agreed well with in-situ observation data (R2~0.8, RMSE~30%, bias~10%). Based on these products, we show a range of additional products that include the ratio of diffuse PAR to total PAR, the ratio of PAR to total shortwave radiation, and the ratio of GPP to absorbed PAR. Finally, we demonstrate spatial and temporal patterns of Rg, PAR and dPAR over the global land between 2001 and 2014. We plan to open these products to public.