SPATIAL VARIABILITY OF IMAGES AND THE MONITORING OF CHANGES IN THE NORMALIZED DIFFERENCE VEGETATION INDEX

Pairs of Landsat Multispectral Scanner System images from seven contra sting areas were analysed using scale variance analysis to determine t he spatial frequencies present. Specifically images of the Normalized Difference Vegetation Index (NDVI) were analysed, which is sensitive t o vegetation activity. Analyses were performed on images for each of t he two dates and change images derived by subtracting the NDVI values of the first images from those of the second date. As expected the cha nge images were characterized by higher spatial frequencies than the i mages of individual dates, but this was only marked for four of the se ven areas. Contrary to initial expectations, knowledge of the spatial frequency content of the images from the two dates could not be used t o infer the spatial frequencies present in the change images and hence the spatial resolutions needed for detecting change in the NDVI.