SUSPECTED MT PINATUBO AEROSOL IMPACT ON THE NOAA AVHRR NDVI OVER INDIA

During regular analysis of the biweekly NOAA AVHRR based Normalised Difference Vegetation Index (NDVI) for drought assessment over India, significantly low values were observed over South India from August 1991 until early 1992. These low values are likely to be due to the effect of aerosol from Mt. Pinatubo eruption in early June 1991. A comparison of NDVI data sets averaged over one degree latitude belts and at different districts over India during 1991 and previous years, indicated lowered NDVI values while ground checks ruled out the contributory effect of drought stress. Analysis of the AVHRR Band 1 and Band 2 values (DN) over sample sites between pre- and post-eruption periods showed disproportionate reduction in band values, thus affecting the NDVI.