NDVI: More information

Normalized Difference Vegetation Index (NDVI) is a measure of the concentration of green vegetation for a given area of the land surface.

The maps and bar graphs show how NDVI in Arctic land areas for different years and months compares to the long-term average for the period 1982 to 2010.  (Data for 1981 are not available). On the map, areas with higher NDVI than the average for the selected month are indicated in greens (positive anomalies), and areas with lower than average NDVI are shown in browns (negative anomalies).  The map of anomalies shows where changes in NDVI are the greatest.

The bar graph indicates the NDVI anomaly for the selected month and year for the entire Arctic land area (the land area north of 60° N). The graph helps to illustrate Arctic-wide changes for each month of the year.

sample ndvi imageThis sample image shows monthly mean NDVI anomalies for June 2008.

Increases in NDVI represent an increase in the amount of green vegetation. In the Arctic, these increases have been linked to both an increase in shrubs and longer growing seasons. 

Changes in NDVI are not as pronounced as changes in near-surface air temperature and sea ice extent. However, like other variables the magnitudes of changes depend on both time of year and location. Changes are largest in summer months, especially July, during the growing season. By contrast, little or no change is visible in winter months when much of the Arctic land surface is covered by snow.  In summer months, there is a tendency for more positive anomalies later in the record.  However, there is some marked variability.

As with the bar chart, changes in the spatial patterns of NDVI are greatest in summer months.  Positive anomalies can be seen in coastal regions of North America and Northern Siberia in recent years.  However, negative anomalies are also present, indicating strong variability in NDVI.

The NDVI data shown here are from the Global Inventory Modeling and Mapping Studies (GIMMS) from the Global Land Cover Facility (www.landcover.org) at the University of Maryland.  NDVI is derived from imagery acquired by the NOAA Advanced Very High Resolution Radiometer (AVHRR) satellite instruments. The data set spans the period from 1981 to 2010.  NDVI is calculated from the amounts of reflected visible and near-infrared radiation measured by remote sensing instruments on-board earth orbiting satellites and also aircraft. Chlorophyll in plant leaves absorbs blue and red wavelengths of solar radiation. This radiation is used in photosynthesis processes. Near-infrared radiation is reflected. The greater the density of green leaves in an area, the more visible light absorbed and the more infrared light reflected, producing a high NDVI index. Areas with sparse vegetation, such as grasslands, tundra or desert, or areas with unhealthy vegetation, such as drought stricken regions, tend to have lower values of NDVI.

Bhatt, U.S., D.A. Walker, M.K. Raynolds, J.C. Comiso, H.E. Epstein, G. Jia, R. Gens, J.E. Pinzon, C.J. Tucker, C.E. Tweedie, and P.J. Webber.  2010.  Circumpolar Arctic Tundra Vegetation Change is Linked to Sea Ice Decline.  Earth Interactions, 14.

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