Research On Glacier Extraction Based On Multisource RS Imagery And Changes Monitoring Of Eastern Tienshan Mountains

Along with intensification of climate change and human activities, dramatical changes have taken place at mountain glaciers in recent decades. Monitoring glacier changes has attracted attentions of researchers and governments. Mountain glaciers densely develop in arid land of Northwestern China, and glacier advance or retreat have important impacts on ecological environment. Meanwhile, glacier changes are indicator of climate change. As reasons of high altitude, diversiform types and relatively poor accessibility of mountain glaciers, traditional ground survey methods can not complete monitoring glacier in a large area. For these reasons, this thesis utilizes multisource remote sensing technology to analyse glacier changes in eastern Tienshan Mountains. Specific researchs are studied and problems are solved as follows.(1) To automatically select extraction threshold of each glacier, this thesis establishes a “global-local” iteration method to slove problems of large differences in spectrum of glaciers in different regions. Normalized Difference Snow Index(NDSI) is applied in this method. This method implements selection of “global” NDSI threshold, and “local” NDSI threshold is adjusted adaptively. Through slope image and shaded relief image derived from Digital Elevation Model(DEM), false informations such as water and shadow are reduced automatically. Glacier boundaries of Bogeda Mountains in single Landsat image are extracted, and results show this method can quickly select “global” and “local” glacier extraction threshold. Precision and efficiency of glacier boundaries extracted by this method are high.(2) For extracting glacier informations covered by mountain shadows and excluding snow interference, a multitemporal remote sensing method is established. Firstly, snow ice boundaries in multi-temporal remote sensing images are extracted. Secondly, glacier boundaries hidden by mountain shadows are restored with topographic features and different sun angle informations of different remote sensing images. Finally, the best glacier extents are intersected by different temporal snow ice extents. In order to validate the method, glacier extraction process is test with 4 temporal Landsat images during 2009 to 2010 in western part of Tumur peak on Tienshan Mountains. Results show that this method performs well in extracting glacier boundaries covered by mountain shadows with multitemporal images, and snow interference is excluded.(3) This thesis maps and analyses glaciers during 1990 to 2010 on eastern Tienshan Mountains using method in this thesis. Regulations in sizes, areas, lengths, aspects, terminus altitudes of glaciers on eastern Tienshan Mountains is analyzed. Results shows that retreat rate of glaciers during 2000 to 2010 is twice as fast as retreat rate during 1990 to 2000. Influences of temperature and precipitation to positioning glaciers on eastern Tienshan Mountains are analyzed. Also, response relationships of glaciers and runoffs in typical basins are established.