Research On Detection Of Glacier Changes In Western China By Remote Sensing

There are a large number of large-scale mountain glaciers in western China.The Tibetan Plateau,in particular,contains the largest ice and snow reserves outside the world's poles,serving as one of the largest modern glacier areas in the low to middle latitudes of the Northern Hemisphere and all around the world.Glaciers are important freshwater resources,and one of the most sensitive factors to climate change.However,glacier surges may trigger glacial disasters that threaten the safety of human life and property.Temperate glaciers are extremely sensitive to climate change,and the flow speed of glaciers is one of the important parameters for understanding the dynamics of glaciers and the response of glaciers to climate.Therefore,measuring the velocities of glaciers is of vital scientific value for studying the climatic and environmental evolution.Glacier surge is a special form of glacier movement.Detecting and studying the glacier surge behaviors is the basis for distinguishing between surge glaciers and non-surge glaciers,and a better understanding of the mechanism of glacial surges.It is also a prerequisite for preventing and predicting glacial disasters.Most of the studies on glacier surges focus in the Karakorum region in western China.Surge behaviors of glaciers in the western Kunlun Mountains,which belong to the extremely continental glaciers,are rarely studied in detail.Glaciers are important freshwater resources,and most of the large rivers in China originate from glacial areas in western China.In particular,sub-continental glaciers are known as “alpine solid freshwater reservoirs”.Glacier mass changes will affect the river runoff,so it is very important to monitor the glacier mass changes with high precision.Remote sensing can provide high-resolution,large-scale,long-term and high-reliability observation data,which can serve as an effective method for glacier change detection.Therefore,this thesis studied these glacier changes in western China based on remote sensing.The main contents and innovations of this research have been summarized as follows:(1)Temperate glaciers are sensitive indicators of climate change,and glacier velocity is one of the important parameters for understanding glacier dynamics and its response to climate.Based on the phase correlation method in frequency domain,Landsat images were used to extract the velocity of the Yanong Glacier from 1995 to 2011,and temporal and spatial variation of the multi-year velocity as well as its controlling factors were analyzed.The results show that the speed of glacier movement decreased significantly and the temperature increased significantly from 1995 to 2011.The speed of glaciers is affected by factors such as topography,tributaries,and terminal lakes.The speed of glaciers at the terminus is relatively high,due to the influence of glacial lakes.(2)To obtain large-scale glacier velocity maps in detail,based on phase correlation method in frequency domain and spatiotemporal median filtering,we obtained three glacier velocity maps of periods 1988/1990,2000/2002 and 2014/2016,in the eastern section of Nyainqentanglha from Landsat images.Statistical methods were used to evaluate the uncertainty of the results.By extracting the centerlines of the velocity maps,we obtained the changes of the glacier velocities in the study area for nearly 30 years.The results show that the 26 studied glaciers in the eastern section of the Nyainqentanglha area are active,but they have experienced significant slowdown since 1988.The rate of slowdown from 1988/1990 to 2014/2016 ranged from 10.78% to 77.46%,which translates to 4.15% to 29.8% per decade.The loss of ice mass causing by the significant increase in temperature should be the main cause of the glacier slowdown in the study area.(3)Most of the studies on glacier surges focus in the Karakorum region in western China.Surge behaviors of glaciers in the western Kunlun Mountains,which belong to the extremely continental glaciers,were rarely studied in detail.Remote-sensing data were utilized to characterize the surge behaviors of Alakesayi Glacier from 2013 to 2018.Glacier surface velocities were estimated by the phase correlation method in frequency domain using Landsat images,and changes in glacier surface elevation were extracted by the DEM differencing method using ASTER DEM and SRTM DEM;terminus and surface morphological features were also measured and interpreted visually from remote sensing images.The detected results show that Alakesayi Glacier had been in surge for at least four years,with the active phase of about two years.DEM differencing results show a thickening of the receiving zone and a thinning of the upstream reservoir zone during the surge.The maximum speed is about 4.5 m/d and the recurrence interval is more than forty years.The active phase of ?2 years is shorter than the surge phase duration of more than 5 years in other surge-type glaciers in the region.These surge behaviors suggest that the surges of Alakesayi Glacier cannot be explained by only either thermal regulation or hydrological regulation.(4)Sub-continental glaciers can function as “alpine solid water reservoirs”,as they will melt in the warm season and replenish the rivers.Therefore,it is very important to monitor the glacier mass changes with high precision.This study proposed a method for estimating the mass changes of mountain glaciers based on interferometry.The proposed method does not need to differentiate between multi-temporal DEMs but uses the interferometric phase,which is sensitive to the surface deformation,to estimate the glacier mass changes,thus achieving higher precision.The seasonal and annual mass changes of the Koxkar Glacier,which belongs to the sub-continental glaciers,are estimated using ERS-1/2 SAR images.It is found that the winter mass changes of the glaciers are consistent with the summer mass changes,and are affected by the glacier surface debris.The effectiveness of the method was validated by the in-situ measured data.