A vegetation index is a simple mathematical formula used to estimate the likelihood that vegetation was actively growing at a particular location whenever it was observed. Most indices were empirically constructed in such a way that larger values correspond to higher probabilities of actually finding live green plants at the selected location and time of observation. As the name implies, the result is a non-dimensional index or indicator of the presence of vegetation.

Global Normalized Difference Vegetation Index (NDVI) from NOAA-AVHRR

The GIMMS (Global Inventory Modeling and Mapping Studies) data set is a normalized difference vegetation index (NDVI) product available for a 25 year period spanning from 1981 to 2006. The data set is derived from imagery obtained from the Advanced Very High Resolution Radiometer (AVHRR) instrument onboard the NOAA satellite series 7, 9, 11, 14, 16 and 17. This is an NDVI dataset that has been corrected for calibration, view geometry, volcanic aerosols, and other effects not related to vegetation change.

Data from IRI Data Library: NVDI data

Spatial resolution: 8km
Temporal resolution: 15-days
Availability: July 1 1981 to Dec 31 2006

Africa Normalized Difference Vegetation Index (NDVI) from NOAA-AVHRR

Africa NDVI product from the NASA GIMMS group called NDVI-g. This dataset is spatially identical to the previous NDVI-e product but has less NDVI signal removed via smoothing. This has resulted in a real-time, operational NDVI product called NDVI-rg that can be compared to the historical archive for identification of anomalous vegetation trends. The dataset is inter-calibrated with SPOT Vegetation NDVI, and uses NOAA-17 data since January 2004. The NOAA-17 NDVI data have also been inter-calibrated with NOAA-16 and previous NDVI products. These data are now available from the ADDS server in WinDisp and generic BIL formats. Note that the NDVI data from July dekad 1, 1981 through March dekad 3, 2005 are NDVI-g. The data from April dekad 1, 2005 to present are NDVI-rg. NASA has stated that the NDVI-rg data will be updated to the archival NDVI-g product approximately every 6-12 months.

From the IRI Data Library: Monthly and Dekadal

Spatial resolution: 8km
Temporal resolution: Monthly and 10-days

Vegetation indices from TERRA-MODIS and single channels (blue-red-NIR-SWIR)

The Moderate Resolution Imaging Spectroradiometer (MODIS) VI products are designed to provide consistent, spatial, and temporal comparisons of global vegetation conditions that can be used to monitor photosynthetic activity. Two MODIS VIs, the normalized difference vegetation index (NDVI) and the enhanced vegetation index (EVI), are produced globally over land at 16-day compositing periods. Whereas the NDVI is chlorophyll sensitive, the EVI is more responsive to canopy structural variations, including leaf area index (LAI), canopy type, plant physiognomy, and canopy architecture. The two VIs complement each other in global vegetation studies and improve upon the detection of vegetation changes and extraction of canopy biophysical parameters. The MODIS NDVI is referred to as the “continuity index” to the existing 20+ year NOAA-AVHRR derived NDVI time series, which could be extended by MODIS data to provide a longer term data record for use in operational monitoring studies. The AVHRR-NDVI has been widely used in various operational applications, including famine early warning systems, land cover classification, health and epidemiology, drought detection, land degradation, deforestation and in relating large-scale inter annual variations in vegetation to climate. The enhanced vegetation index (EVI) is an ‘optimized’ vegetation index with improved sensitivity in 11 high biomass regions and improved vegetation monitoring through a de-coupling of the canopy background signal and a reduction in atmosphere influences. The MODIS single channel reflectance values in the Blue-Red-NIR and SWIR are used in combination to detect water bodies, bare soils, and vegetation (Ceccato, 2005). A false color composite based on a Red-Green-Blue colors—where the Red color is associated to the SWIR, the Green color is associated to the NIR, and the Blue color is associated to the Red channel—provides an image where the vegetation is represented in green, bare soils in brown, and water bodies in blue. This false color composite is available via the IRI Data Library. Estimation of vegetation water content is another biophysical property that is central to the understanding of biomass burning processes. It has been shown that the shortwave infrared (SWIR) and the near infrared (NIR) wavelength ranges are necessary for retrieving vegetation water content in terms of water quantity per unit area at canopy level (Ceccato et al., 2001, Ceccato et al., 2002a,b). Using the IRI Data Library, it is possible to create vegetation indices targeted to monitor vegetation moisture content such as the NDWI (Gao, 1996).

From the IRI Data Library: MODIS

From the Maproom within the Health, Food Security, and Fires sections.

Spatial resolution: 250m
Temporal resolution: available every 16 days