RELATIONSHIP OF A GLOBAL VEGETATION INDEX TO WORLD SOILS 
Norman B. Bliss^ and Kevin P. Gallo^ 
ABSTRACT 
A global vegetation index was compared with information on soil properties by using a geographic information 
system. The soil properties were interpreted from the FAO/UNESCO Soil Map of the World (1:5,000,000 
scale), compiled by the Food and Agriculture Organization of the United Nations and published by the United 
Nations Educational, Scientific, and Cultural Organization. This map is the most complete source of digital 
soil data available on a worldwide basis. 
The global vegetation index was produced as a composite of Normalized Difference Vegetation Index (NDVI) 
data derived from the National Oceanic and Atmospheric Administration’s Advanced Very High Resolution 
Radiometer (AVHRR). The NDVI was computed as the difference between the reflectance data in the 
infrared and visible wavebands divided by their sum. 
Preliminary results of statistical analyses of relationships between the two data sources show that variations in 
the vegetation index data are related to the soil map units. The soil map units were used to stratify the 
vegetation index data. The vegetation index data were cumulated over the period of a year to create a data 
set of NDVI days. The mean NDVI days were significantly different between soil map units. 
y TGS Technology, Inc. Work performed under U.S. Geological Survey contract 
14-08-0001-22521. 
y NOAA/NESDIS, EROS Data Center, Sioux Falls, SD 57198 
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