Use of multitemporal satellite images to find some evidence for glacier changes in the Haft-Khan glacier, Iran

摘要

Present paper reports on the Haft-Khan glacier clean-ice area change between 1955 and 2010 based on several high to medium spatial resolution satellite images. Present glacier is heavily covered by debris (referred as supra-glacial debris cover). Because of these covers, mapping the actual glacier area with reasonable accuracy is impossible. Therefore, the changes of clean-ice regions have been detected as a good evidence for glacier change. For the detection of these changes, nine high to medium spatial resolution satellite images were selected. Although these images are the best available satellite images in Haft-Khan Glacier (to avoid any misclassification), but the possible changes in perennial snow fields cannot be separated from the clean-ice area changes. It means that some of the obtained changes may also be related to the changes in perennial snow fields not the absolute change of clean-ice regions. The object-oriented classification approach has been used to estimate the clean-ice glaciated areas. Object-oriented classification method takes into account the shapes of the features along with their spectral patterns. In the last decades, advantages in computer technologies have led to the development of object-based image analysis; an image classification technique that can be seen as an alternative to the common pixel-based image analysis and manual digitization. Results revealed that debris-free areas of Haft-Khan glacier shrank since 2010 with an overall area reduction of about 58 +/- 5 %. Although the general trend is clean-ice area reduction, some limited area gain has been observed over the period of 2003-2010. During the 1992-2000, the maximum reduction in the clean-ice area was observed (0.13 +/- 0.009 km(2) a(-1)). However, during the 2003-2010, the areas of clean-ice regions have steadily increased. Fractional snow cover (FSC) change during the last 34 years (1979-2013) revealed that precipitation during the accumulation period (from November to May of the following year) decreased significantly, reducing the snowfall contribution to mean balance. This is the main reason for the clean-ice area shrinkage in the Haft-Khan glacier.