Examining the Suitable Time for Using Satellite Images to Study Different Vegetation

Studying and monitoring the vegetation in all ecosystems, especially rangeland and forest ecosystems, is of a particular importance. Given that the large area and the changing nature of these regions make their management difficult, today the satellite images are used as cost effective and handy equipment for this purpose. Considering the qualitative and quantitative changes of the vegetation during the growth season, choosing the appropriate time and type of satellite images should carefully be taken into consideration. The present study was carried out in an attempt to determine the most appropriate time for using satellite images to examine the vegetation in rangeland and forest ecosystems in Isfahan and Chaharmahal o Bakhtiari provinces. For so doing, the relation between the green vegetation and the Normalized Difference Vegetation Index (NDVI) as well as their correlation coefficient during the growth season were investigated in three rangelands and a forest. To calculate the relationships between vegetation and NDVI, the ground data and six series of Landsat images during the growth season were used. The results showed that the correlation coefficient between NDVI and vegetation cover percentage in different phenological stages within each vegetation type as well as among different vegetation types was different. Depending on the type and life form of vegetation, at the end of the growth period, the correlation coefficient between vegetation and NDVI decreases. The highest and lowest variation in NDVI and its correlation with vegetation were observed in grassland and forest types, respectively. According to the aforementioned results, it can be concluded that the time of study for vegetation monitoring by remote sensing is very important.