District level NOAA/AVHRR vegetation indices 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° to 19-10° in different dates images indicated an increase in its value with an increase in scan angle except for pixels dominated by water surface features.