One kilometer resolution SPOT VEGETATION subsets were extracted from continental, maximum- value composited NDVI over land areas. NDVI is the difference (in reflectance) between the near-infrared and visible bands divided by the sum of these two bands.
Ten-day composite image data were constructed by selecting pixels with the maximum NDVI during the period. Selecting pixels with maximum NDVI reduces cloud cover and water vapor effects that strongly reduce NDVI. Compositing can be performed over any time interval, but 9-10 days is generally selected as the minimum period for maximum quality. There are three 10-day composites per month in this data set, from the first of the month to the 10th, from the 11th to the 20th, and from the 21st to the end of the month.
The files in this data set are named with the following naming convention:
SP refers to the SPOT satellite
CC is one of the following continent codes
- AF = Africa
- AZ = Australia and New Zealand
- EA = Eurasia
- NA = North America
- SA = South America and Central America
name is the DAAC core site name of the subset
num is an arbitrary site number
ext is the file suffix, where img refers to the data cube file type, and hdr refers to the associated ascii header file
Each file is comprised of 227 10-day maximum-value composite (MVC) NDVI bands, from May 10, 1998 to May 31, 2004. There are 3 images, or bands, per month. The names designated in the header file contain dates that refer to the end-date of the compositing period. The last compositing period can vary from 8-11 days, depending upon the number of days in the month. The images are 201 lines by 201 pixels in size, and are geolocated using the accompanying ENVI ascii header file. The image projection is Albers Equal Area Conic.
SPOT Vegetation Data provided by United States Department of Agriculture/Foreign Agricultural Service (USDA/FAS) through collaboration with the GIMMS Group at NASA/GSFC.