Areas of Glaciers and Glacial Lakes in North-Eastern Nepal studied with Landsat Imagery between 1992 and 2015

摘要

The passive remote sensing of Landsat images gives a great opportunity to look at the glaciers and the glacial lakes in the Himalayas and construct a time series to assess the changes which has occurred over the years. After analyzing different methods to map clean glaciers, debris covered glaciers and glacial lakes, a method combining supervised classification of the Landsat image and morphometric parameters (slope and aspect) derived from global digital elevation model (ASTER GDEM) was applied to map the glaciers and glacial lakes in the northeastern Himalayas of Nepal and bordering areas of Tibetan plateau. Furthermore, manual intervention was also done for the debris covered glaciers and glacial lakes to reduce the noises and improve the accuracy. A time series was constructed after mapping which included the years 1992,1995,1998,2008 and 2015 with 1992 as the reference year. An apparent melting trend for the clean glaciers was seen with coefficient of regression of 0.56 and a loss rate of-10.54 km2 per year for the period of 23 years (1992-2015). For the debris covered glaciers and glacial lakes, a fluctuating behavior with no trend was seen. However, a clear trend of expansion of the supraglacial lakes on top of the debris covered glaciers was seen with the regression coefficient of more than 0.9 and a rate of expansion of 0.11 km~2 per year. A total of 6 lakes in the study area were seen to be expanding significantly since 1992.Although glaciers and glacial lakes could be mapped with satisfactory results, the results could be improved by using high resolution imagery in combination with Landsat. Moreover, using radar based remote sensing to map the glaciers and glacial lakes in the Himalayas could mitigate the problem of cloud cover which was one of the major hindrances in this study.