Analysing different groups of remote sensing vegetation indices for studying rangeland vegetation types
Satellite images are currently used as a fast and low-cost solution for rangeland assessment. In this study, 10 vegetation indices from different groups were calculated using spectral bands. The correlation of these vegetation indices with canopy cover was then measured for three vegetation types in Semirom region, Isfahan. The percentage of canopy cover and other earth surface components such as litter, rock, gravel, stone and bare ground was determined using step-point method. First 10 random points were selected and then four 150 meter transects in radial direction were established from each point in which 6000 points were studied per rangeland type. Ten different groups of vegetation indices including slope-based, distance-based and plant–water sensitive indices extracted from IRS-P6 satellite data (AWiFS sensor) were evaluated against field cover. The results indicated that vegetation indices have higher relationships within vegetation types based on their characteristics but the correlation for each vegetation index was not consistent among different types. Considering all photosynthetic vegetation cover, the correlation with vegetation indices was much higher whereas in degraded rangeland due to less green vegetation cover and less photosynthetic activity the correlation decreased. Overall, the results indicate that each vegetation index is appropriate for mapping a specific vegetation type and we should consider this issue in mapping and monitoring vegetation cover.