GPPDownload: Download MODIS GPP (Gross Primary Product).
NPPDownload: Download MODIS NPP (Net Primary Product).
SAR: Process SAR data of Sentinel-1. Refered from https://github.com/adugnag/gee_s1_ard.
RSEI: Use Sentinel-2A/B data to calculate RSEI (Remote Sensing Ecological Index).