| Glaciers and glacial lakes are important research objects of climate change,regional water resources change and glacial geological disasters.Remote sensing technology plays an increasingly important role in Glacier research because of its rapid development,non-contact and macro characteristics.Therefore,the middle Himalayan region with well-developed glaciers and glacial lakes is selected as the research area,and the application of optical remote sensing technology in the field of glacier and glacial lake change monitoring is explored from three aspects: glaciers surface velocity change,debris-covered glaciers area change,net glacier and glacier lakes area change.(1)Aiming at a series of errors existing in the extraction of glacier surface velocity by optical offset technique,the glacier velocity fields of 1994 and 2018 in the study area were obtained by using a series of error processing methods.According to the distribution of stable regional values and glacier velocity results,the obtained glacier velocity field is more reliable and the accuracy is significantly improved.The velocity changes of four representative glaciers show that,compared with 1994,the velocity of net glacier and surface moraine glacier decreased by more than 40% in 2018,and the change is obvious;by 2018,the end of the two surface moraine glaciers has evolved into a dead ice area,and the end of the net glacier has obviously accelerated due to the advance of the ice lake,which has become a serious warning of glacier fracture.(2)In order to solve the problem that it is difficult to extract the debris-covered glaciers with high precision in a large scale,this paper uses the factors such as velocity,texture and terrain,combined with the random forest classification model to extract the debris-covered glaciers in the study area automatically.The advantages and reliability of this method are proved by comparative experiments and sensitivity indexes.The sensitivity is as high as 87.70%,and the sensitivity of large debris-covered glaciers is higher.Therefore,the sensitivity will be further improved if the debris-covered glaciers are extracted on a larger scale.The results show that the debris-covered glaciers area is 201.45km2 in 2018 and 179.12km2 in 1994.The main reason is that the tip of a large number of naked glaciers retreated and evolved into the debriscovered glaciers.(3)Based on the Landsat series images from 1994 to 2018,the object-oriented threshold classification method is used.In the process of classification,the accuracy of glacier classification is improved by using the previous temporal glacier vector results as a reference and eliminating the snowfall around the boundary.The results show that the net glacier in this area is mainly retreating at a rate of 1.28 ± 0.32% / y,and the glacial lake is expanding rapidly at a rate of 1.88 ± 1.07% / y.The analysis of the meteorological data shows that the average temperature and the total amount of summer precipitation in this area have an upward trend.The average temperature in summer has increased at the rate of 0.035 ? per year,and even increased by about 1.8 ? since 2010.The summer precipitation increased at a rate of 15.822 mm / y,and increased nearly 500 mm in 29 years.The increase of temperature and precipitation in summer is the main reason for the increase of glacier retreat rate.At the same time,the increase of precipitation and the accelerated retreat of glaciers jointly promote the expansion of the ice lake and increase the risk of ice lake outburst.From the perspective of internal factors,the smaller the glacier area is,the greater the retreat rate is.Therefore,in the long run,with the decrease of glacier area,the same temperature change will bring higher retreat rate... |
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