DISTRICT LEVEL NOAA/AVHRR VEGETATION INDEXES AND SCAN ANGLE EFFECTS

Data sets were collected on five consecutive dates over a district (3684 pixels) having 86.83 per cent of sown area and 75 per cent of total land use area under rice cultivation. The study of statistical mean and standard deviation for the geometrically-corrected Normalised Difference Vegetation Index (NDVI) and Ratio Vegetation Index (RVI) images of these five dates did not show significant variations. Pixel-by-pixel based studies using difference of consecutive dates NDVI/RVI images indicated that 95 97 per cent of variations for difference consecutive dates pairs were covered within - 0.09 to + 0.09 and - 0.25 to + 0.24 ranges for NDVI and RVI respectively. Typical behaviour of consecutive dates NDVI scatterograms have been discussed. Study of near-infrared (IR) spectral band digital count value for 12 ground control points (GCPs) spread over scan angle ranges from 35.12-degrees to 19.10-degrees in different dates images indicated an increase in its value with an increase in scan angle except for pixels dominated by water surface features.