عنوان مقاله [English]
Using modern techniques especially remote sensing, it is possible to investigate the vegetation of a wide area in a shortest time with lowest cost and high accuracy. In this research, the images associated with 1986, 1992, 1998, 2004, 2010, 2016 have been provided to evaluate the changes in area and quality of vegetation in 13 districts of Mashhad city using ETM, TM5, MSS, OLI evaluators of Landsat satellite. An NDVI index has been used to evaluate these quantitative and qualitative changes. To achieve the quantitative changes of vegetation in mentioned years, districts have been classified in two groups: districts with vegetation and districts without vegetation. The results illustrate that the area of vegetation has decreased from 38.14 square kilometers in 1987 to 32.97 square kilometers in 2016. Among all districts, most vegetation changes has occurred in district 3 from 1998 to 2004. The vegetation decreased from 8.64 square kilometers in 1998 to 3.99 square kilometers in 2004 and the decline was 4.63 square kilometers. To achieve the qualitative changes of vegetation, districts have been categorized in three groups: districts without vegetation, districts with medium vegetation and districts with dense vegetation. The results have shown that the total dense vegetation has increased from 0.413 square kilometers in 1987 to 3.321 square kilometers in 2016. District 13 had no dense vegetation and district 2 had the most density with 0.958 square kilometers in 2016.