AVHRR NDVI Subsets
Subsets extracted from the Global Inventory Modeling and Mapping Studies (GIMMS) Satellite Drift Corrected and NOAA-16 Incorporated Normalized Difference Vegetation Index (NDVI), Bi-monthly, 8 km, 1981-2003
These data were extracted from continental, composited, bi-monthly, NDVI over land areas. NDVI is the difference (in reflectance) between the AVHRR near-infrared and visible bands divided by the sum of these two bands (Tucker 1980; Sellers 1985; Sellers et al. 1994).
Frequent cloud cover can create numerous gaps in the daily AVHRR record, eliminating roughly two-thirds of the data. In order to construct cloud-free views of the Earth, composite images were constructed at regular intervals by selecting pixels with the maximum NDVI. Choosing pixels with maximum NDVI reduces cloud cover and water vapor effects since both strongly reduce NDVI. Compositing can be done over any time interval, but 9-10 days is generally selected as the minimum period for maximum quality. The GIMMS data record constructed here is based on nominal 15-day composites. There are two 15-day composites per month, the first for day 1-15, and the second for day 16 to the end of the month.
The files in this data set are named using the following naming convention:
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 has 550 (bi-monthly maximum-value composite NDVI image bands, from July 1, 1981 to May 31, 2004. For each month there are two images, the names designated in the header file with an `a` refer to the subset for the first half of the month, and the `b` designator refers to the subset for the second half of the month. The files are 25 x 25 pixels in dimension, geolocated in the accompanying ENVI header file.
As of October 2004, the complete global 8km data set is available at the Global Land Cover Facility at the University of Maryland. This file is a subset of these data. To properly reference this AVHRR NDVI dataset, please cite the following two papers:
Pinzon, J., Brown, M.E. and Tucker, C.J., 2005. Satellite time series correction of orbital drift artifacts using empirical mode decomposition. In: N. Huang (Editor), Hilbert-Huang Transform: Introduction and Applications, pp. Chapter 10, Part II. Applications.
Tucker, C.J. et al., 2005. An Extended AVHRR 8-km NDVI Data Set Compatible with MODIS and SPOT Vegetation NDVI Data. International Journal of Remote Sensing, submitted.