Using vegetation indices (VI) for an inventory of natural ecosystem has been developed over the past decades. Also these VIs have been observed to have a suitable correlation with vegetation parameters.
However, to apply VI over a continuous span of time some considerations should be taken into
account. In order to study the capability of multi-temporal Landsat 7 (ETM+) data in estimating
vegetation parameters, different year images in a steppe region in Markazy Province were used.
Information of regarding canopy cover and production of different vegetation forms were collected through 60 2x2 plot s.Geometri c cor rect ion of sat ellite images was conducted through ground control points with an RMSE of less than 0.5 pixel. Then to eliminate the effects of looking geometric situation as well as to make photography situation in different years uniform, radiometric correction was conducted, and digital number of each pixel converted into spectral reflectance. In the next stage, appropriate VI for arid region s and atmo spheri c correction VI in sample plots were asses sed on the basis of spectral reflectance. Result s of correlation survey between VI and vegetation parameters indicated that ETM5, ETM7 bands as well as TSAVII, GEMI and ARVI indices are in significant correlation with canopy as well as with production in different vegetation forms. Among VIs , GEMI exhibits the highest coefficients, of 0.43 , 0.59, 0.63, and 0.55 , for grass cover, shrub cover and total vegetation cover as well as for production respectively. According to the results in this research this conclusion can be drawn that using spectral reflectance of multi temporal data to estimate vegetation canopy cover and
yield in arid regions can yield more acceptable results. Employment of atmospheric correction indices (GEMI) to decrease changes in atmospheric conditions in different years is necessitated.