VEGETATION INDEXES FROM AVHRR - AN UPDATE AND FUTURE-PROSPECTS

Procedures that are currently applied to data from Advanced Very High Resolution Radiometer (AVHRR) in deriving vegetation indices are analyzed. It is shown that the type of compositing used has a great impact on the final product. Some misconceptions concerning the global vegetation index (GVI) data set are discussed. Cloud-screened daily data over Kansas prairie during 1 month were used to develop a viewing angle correction for the observed range of sun angles and for that particular surface type. This example indicates that the variability in the calculated vegetation indices could be reduced, thus raising the confidence level in statistical comparisons of observations for different years. The correction developed is applied to a different crop area and improvement in the results is demonstrated. Errors in the calculations are analyzed. Prospects for future improvements in processing vegetation index data are discussed.