A study on vegetation vigour as affected by soil properties using remote sensing approach

Vegetation is a complex phenomenon with large amount of inherent spectral, spatial and temporal variability and it is typically characterized by strong absorption in the red wavelengths and high reflectance in the near infra-red (NIR) wavelengths of the electromagnetic spectrum. The images generating from various Vegetation Indices like Normalized Difference Vegetation Index (NDVI), Normalized Difference Water Index (NDWI) etc. from multispectral imagery can provide valuable vegetation information about an area. Soil background conditions exert considerable influence on partial canopy spectra and calculated vegetation indices. Therefore, it is important to monitor the vegetation vigour changes with respect to the soil background conditions. For this purpose, a suitable remote sensing based algorithm i.e. Soil Adjusted Vegetation Index (SAVI) was selected and applied for the study. The analysis of vegetation vigour changes was done for different time series in the part of Andhra Pradesh state. The MODIS vegetation index images of 250m resolution were used. NDVI and NDWI images were derived for red and black soil types, with reference to that the SAVI model was created and executed in ERDAS IMAGINE platform. In SAVI equation, the soil adjusted factor `L´ was modified with different values and multivariate SAVI images were derived for both red and black soil regions. In the various red soil regions, the SAVI with `L´ value as 0.25, 0.3, 0.4 and 0.5 produced the fair result on soil and vegetation reflectance variations over the crop season. Similarly in the different black soil region, the vegetation cover is medium and SAVI with `L´ value as 0.3 and 0.4 produced the fair result on soil and vegetation variation. This study was done with only the two types of soil regions and with minimal datasets. The analysis part of the study can be extended with multiple data sets and different seasons.