Where can I find a reliable source of global spatial data for net primary productivity (NPP)?
I have looked and looked but have met various road blocks.
what are your desired formats and resolution (temporal and spatial)? A quick search found many global products derived from MODIS, e.g.:
Gross Primary Productivity 8-Day L4 Global 1km https://lpdaac.usgs.gov/dataset_discovery/modis/modis_products_table/mod17a2
Terra/MODIS Net Primary Production Yearly L4 Global 1km https://lpdaac.usgs.gov/dataset_discovery/modis/modis_products_table/mod17a3
UMT MODIS GPP/NPP Project (MOD17)
For the USGS LP DAAC products, this page describes options for data access