National Aeronautics and Space Administration

User GuidePI - Maosheng Zhao (SSAI/NASA GSFC)
Product ATBDCo-Is: Arthur Endsley (University of Montana), John Kimball (University of Montana), Sadashiva Devadiga (NASA GSFC)

The Gross and Net Primary Production (GPP/NPP) data products are designed to provide an accurate regular measure of the growth of the terrestrial vegetation. Primary Production is determined by first computing a daily GPP and net photosynthesis (PsnNet) values which are then composited over an 8-day interval of observations. At the end of each year, all daily GPP and PsnNet are summarized and live wood respiration is subtracted to get annual total GPP and NPP.

The algorithm of the VIIRS GPP and NPP is based on the radiation use efficiency concept and the Q10 theory of plant respiration to changes in temperature. The data products may be used as inputs to data models for calculating terrestrial energy, carbon, water cycle processes, and biogeochemistry of vegetation. Modification of parameters in the Biome Property Look-Up Table (BPLUT) has been made to agree with GPP derived from measurements at eddy flux towers and synthesized NPP.

The issue of the cloud contaminated remotely sensed inputs of 8-day VIIRS FPAR/LAI to the GPP and NPP data products has been addressed. For the operational forward 8-day GPP and PsnNet, the 5-year rolling climatology FPAR/LAI are being used as backup to replace the contaminated values in the inputs to the forward 8-day GPP and PsnNet data products. More importantly, in each early year, year-end gap filled 8-day GPP and PsnNet and annual GPP and NPP of the previous year will be created which use the year-end gap-filled VIIRS FPAR/LAI of the previous year as inputs to the algorithm to clean the cloud contaminated data more thoroughly. We suggest users to use gap filled VIIRS GPP, PsnNet and NPP (with “GF” in the HDF file names) for their studies if these studies don’t require the data for the present year. This is because the present year only has forward data products (without “GF” in the HDF file names) and year-end gap filled data products are only for the previous years and can be created only when the full 8-day VIIRS FPAR/LAI for an entire year are available. In addition, for annual 17A3 GPP and NPP, there are only the gap-filled but not forward data products.

The products are provided in standard Hierarchical Data Format–Earth Observing System (HDF-EOS5) format. Currently, this collection is available from January 19, 2012 and forward.  Products from the VIIRS sensor aboard JPSS-1 (J1) will be also be available starting in mid-2023.

 

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