New oprational real-time daily rolling weekly Green Vegetation fraction product derived from suomi NPP VIIRS reflectance data

摘要

Real-time global Green Vegetation fraction (GVF) is needed in numerical weather, climate and hydrological models. The current NOAA operational GVF product is derived from AVHRR top of atmosphere NDVI data. As part of the NOAA SNPP Data Exploitation (NDE) program, NOAA scientists developed a new near real time GVF product, which is based on the Enhanced Vegetation Index (EVI) derived from the VIIRS sensor onboard the SNPP satellite. The GVF product has two components. The first GVF product has global coverage at 4 km resolution, and the second GVF product is regional (Lat 90°N - 7.5°S, Lon 130°E - 30°E) at 1km resolution. Both GVF products are weekly composites, updated daily based on the past week's data. This new VIIRS GVF product has been operational and available to the public on the NOAA Comprehensive Large Array-data Stewardship System (CLASS) since February 2015. The retrieval algorithm of the VIIRS GVF product uses VIIRS red (I1), near-infrared (I2) and blue (M3) bands centered at 0.640 μm, 0.865 μm and 0.490 μm, respectively, to calculate the Enhanced Vegetation Index (EVI). A novel weekly EVI compositing method is used to select the optimal observations for each grid cell. High frequency noise in EVI time series is reduced by applying a digital smoothing filter on EVI. GVF is calculated by comparing the smooth EVI against the global maximum and minimum EVI values assuming a linear relationship between EVI and GVF. More validation work and testing is needed to determine the benefits of the new VIIRS GVF product over the AVHRR GVF product.