A nine-year (1982-1990) global normalized difference vegetation index (NDVI) data set with a spatial resolution of 1 degree by 1 degree and a temporal resolution of one month was compiled for use in climate studies. This data set was derived from higher resolution (5-8 km) monthly continental NDVI data sets that have been processed and archived by the Global Inventory Monitoring and Modelling Studies (GIMMS) group at NASA/Goddard Space Flight Center. The continental GIMMS NDVI data sets were calculated from Global Area Coverage (GAC) data collected at daily intervals by the Advanced Very High Resolution Radiometer (AVHRR) onboard the NOAA-7, -9 and -11 satellites. The global 1 degree by 1 degree NDVI data set was produced to calculate land surface parameters for use within general circulation model J of the atmosphere (GCM). In view of this quantitative application, an evaluation is given of the representation by the NDVI data of the spectral properties of vegetation at the landsurface. Errors are defined as deviations from measurements obtained under standard conditions, i.e., conditions at the-top-of-the-atmosphere with no clouds, clear atmosphere, near-nadir viewing angles, overhead Sun, and invariant soil background. The discussion includes an assessment of (1) the data collected and processed onboard the AVHRR; (2) processing of the AVHRR data into the continental GIMMS NDVI data sets; (3) resampling of the continental data sets to a 1 degree by 1 degree data set; and (4) propagation of inconsistencies and biases from (1), (2) and (3) into the 1 degree by 1 degree global NDVI data. Examples are shown of the temporal and spatial variations in spectral properties of vegetation contained in the 1 degree by 1 degree NDVI data, and these are compared with the dynamics of biophysical parameters derived from land cover classes that were used in previous climate studies.
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