Article Global pattern of NPP to GPP ratio derived from MODIS data: ...

Hello Wesley Boone ,

The following site might be of interest for you:

http://silvis.forest.wisc.edu/data/dhis/

I do not know if you can also download averaged data over multiple years, but as far as I know you can download data for each year separately and then manually average it by using a geographic information system.

I hope this helps!

Paul

You can use Google Earth Engine to customize your dataset as you want _

Dear Wesley,

You can use the Google Earth engine, as there are different products available for the region and time you mentioned.

Also, you can refer to this recent paper, where we have used long term NDVI averaging:

Article The Grass Is Not Always Greener on the Other Side: Seasonal ...

Cheers