VIIRS-Based High-Resolution Spectral Vegetation Indices for Quantitative Assessment of Vegetation Health

The Visible Infrared Imaging Radiometer Suite (VIIRS) is one of the main SNPP instruments (JPSS 2014) used for monitoring earth surface, environment and its impact on socioeconomics, including food security through drought detection, monitoring and prediction of agricultural losses, using vegetation health (VH) system (Kogan 1997, 2001). The VIIRS accommodates the best technical and scientific features of its USA predecessors: 36 years of the Advanced Very High Resolution Radiometer’s (AVHRR) excellent work on NOAA polar-orbiting operational satellites and 15 years of Moderate Resolution Imaging Spectra Radiometer (MODIS) on NASA/TERRA and AQUA scientific satellites. The VH method stems from properties of green vegetation to reflect sunlight and emit absorbed solar radiation. Three important steps in the VH algorithm development are derivation of no-noise (smoothed) NDVI and BT (sNDVI and sBT), sNDVI and sBT climatology (multi-year aggregated values) and calculation of weekly departure of weekly sNDVI and sBT from their weekly climatology. In the three steps, derivation of sNDVI and sBT climatology is considered as the most critical. Five years of VIIRS observation is too short for a stable climatology. Formerly, we also tried to directly use AVHRR climatology, and convert VIIRS weekly sNDVI and sBT to the similar AVHRR data using regression equations. Yet both approaches yield inaccurate outcome, comparing to AVHRR-based VH and United States Drought Monitor (USDM) results. Here we utilize Five years of VIIRS observation, while incorporating 36 years of AVHRR information, to build a pseudo 36-year VIIRS climatology, and derive weekly products based on this climatology. The new climatology and product is demonstrated to be much more accurate, which helps to improve the VIIRS VH system, such that the high resolution spectral vegetation incices could be used in multi-scale applications, from coarser coninental, to finer regional ones.