Reliability of ETM+ and TM data for estimating vegetation cover of arid areas rangelands (case study Markazi province of Iran)

Importance of permanent range assessment is advice, because of continuous change, ecological aspects and economy of rangelands. The wide area of rangelands and facilities limitation for regular monitoring cause the requirement of the remote sensing application. The objective of present study was investigation on reliability of ETM+ data for vegetation estimation. The study was carried out in Markazi province for five years. Satellite data of same time of grand truth data was obtained for each year. Vegetation indices were calculated after radiometric and geometric correction of images.Canopy cover of annual species, herbaceous species, grasses, shrub and total cover in five sites during five years were measured. Measurements were carried out in 60 plots two square meters rectangular quadrates along four 400 meter parallel transects. Before processing of the information, 15 random selected quadrates were kept for test of equation. In other case all data of four years was applied to calculate equation between vegetation indices and ground data and data of fifth years was used for test of model. Considering small area of quadrates against 30*30 meter pixel and probability of error involved with coordinate measurement by GPS correlation between mean dataof each transect and indices also was studied. The results obtained from equation were compared with actual cover data using student t-test. Most indices have significant correlation with cover data, however sometimes equation did not gave correct estimation of cover compared with actual data.This was happened for life form that did not make considerable percent of vegetation composition.Generally application of transect data and calculation of equation based on four years data to estimate of fifth years canopy cover was more suitable way of using satellites data. Certainly using satellite system with more bands and better resolution and doing soil background correlation in arid regions would give better results.