The visible part (400700nm) of insolation is called photosynthetically active radiation (PAR). PAR constitutes the basic source of energy for biomass by controlling the photosynthetic rate of organisms on land, thus directly affecting plant growth. It is an indispensable variable in calculating gross primary production (GPP) or net primary production (NPP).GLASS PAR product was generated with 5 km spatial resolution and 3 hours temporal resolution from multiple polar-orbiting and geostationary satellites data globally using an improved look-up table method by radiative simulation based on MODTRAN. The basic idea of this improved algorithm is to establish the relationship between the surface radiation flux and top-of-atmosphere radiance through radiation simulation The satellite data include Moderate-Resolution Imaging Spectroradiometer (MODIS), the Meteosat Second Generation (MSG) SEVIRI, the Multi-functional Transport Satellite (MTSAT)-1R, and the Geostationary Operational Environmental Satellite (GOES) Imager (East and West).

For further details please consult publication(s):

Zhang, X., Liang, S., Wu, H., & Zhou, G. (2013). Mapping Global Incident Downward Shortwave Radiation and Photosynthetically Active Radiation Over Land Surfaces Using Multiple Satellite Data. Journal of Geophysical Research, Undergoing review.
Liang, S.L., Zheng, T., Liu, R.G., Fang, H.L., Tsay, S.C., & Running, S. (2006). Estimation of incident photosynthetically active radiation from Moderate Resolution Imaging Spectrometer data. Journal of Geophysical Research-Atmospheres, 111, 13

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