| For our country,mountain glaciers can not only provide abundant fresh water resources,but also provide important guarantees for the economic development of oasis and the environmental stability of cold and arid areas,which has very important value.However,in recent years,with the continuous warming of the global climate and the impact of human activities,most of our glaciers are in a state of thinning and negative material balance,which has caused a series of sudden glaciers such as shortage of freshwater resources,climate change,glacial lake outbursts,and mudslides.Disasters have a huge impact on people's production and life.Therefore,studying the surface elevation and material balance changes of mountain glaciers can provide theoretical and data support for freshwater resource assessment and climate change analysis,and provide early warning and prevention for glacier disasters such as glacial lake outbursts.To this end,this article has done the following:First of all,this article combs the current commonly used methods for studying glacier surface elevation and material balance changes,and comprehensively considers the advantages and disadvantages of each method and the topographic characteristics of mountain glaciers.Finally,this article chooses the multi-temporal DEM difference method to estimate the glacier surface elevation change,and chooses the geodetic method estimates changes in the material balance of the glacier.However,since the commonly used DEM data are mostly concentrated after 2000,it is difficult to use these data to monitor changes in a long time series,and cannot reflect the early surface elevation changes of the glacier.In order to solve this problem,this paper extracts the DEM data of the study area in 1968 using the KH-4B stereo image with the highest resolution of the American CORONA project series.Secondly,due to the differences in the stability of different satellite sensors during operation and the ground observation environment in different time periods are not exactly the same,it is impossible to accurately align the DEMs of different sources.Therefore,the multitemporal DEM must be differentiated before proceeding.Perform precise registration.The current common registration method is to first judge whether there is an obvious cosine relationship between the ratio of the elevation difference between the two DEMs and the slope tangent of the stable area and the aspect.If so,use the least square method to find the relative level.The offset is then implemented in Arc GIS for registration.However,because the least square method is not robust,sensitive to gross errors,and has a certain impact on the registration accuracy,this article will use the robust IGG? robust function to solve the offset and improve the multi-temporal DEM registration accuracy.Thirdly,based on KH-4B DEM data extracted from stereo images and SRTM,AW3 D,Tan DEM data,the multi-temporal DEM difference method and geodetic method are used to estimate the surface elevation and material of the Gongga Mountain in the nearly 50 years from 1968 to 2013.Balance changes,combined with the precipitation and temperature data from Jiulong and Kangding meteorological stations,analyzed the response of glaciers to climate.Finally,the similarities and differences of the glaciers on the east and west slopes are compared,and the factors such as orientation,slope,and surface moraine coverage are analyzed.research shows:(1)From the perspective of the changes in the elevation of the glacier surface,the glacier as a whole is in a thinning state,and the thickness of the end of the glacier tongue is seriously thinning.As the altitude continues to rise,the thickness thinning phenomenon gradually stabilizes,and the degree of change is small.From 1968 to 2013,the average thickness change of the glacier surface was-26.89±3.20 m,and the average annual change was-0.58±0.07m/a;and the average thickness change rate was different in different time periods,and it has been accelerating in recent years.(2)From the perspective of changes in the glacier material balance,the glacier as a whole is in a state of material loss.Between 1968 and 2013,the average material balance of the glacier was-22.50 ± 1.80 m we,and the average annual change was-0.50 ± 0.04 m we/a.Like the rate of thickness change,it has shown a significant acceleration in recent years.The main reason for this change is that the continuous increase in temperature has caused the melting of glaciers to increase year by year,while the relatively stable precipitation keeps the accumulation of glaciers basically unchanged,so that the amount of glaciers gradually exceeds the accumulation.This change is exactly the state of mountain glaciers in response to climate change.The extent of material loss of glaciers on the east and west slopes is different.(3)The material loss of Hailuogou No.1 Glacier and Hailuogou No.2 Glacier on the east slope is significantly higher than that of Da Gongba Glacier and Xiao Gongba Glacier on the west slope,and Hailuogou No.1 Glacier The material loss of glaciers is the most serious.The loss of the glacier material on the east slope is more serious because it is slightly larger than the average slope of the west slope and the surface moraine cover that promotes the acceleration of ablation,while the Hailuogou No.1 Glacier has the most serious loss because the end of its ice tongue drops to about 2990 m,making the terminal ice surface temperature higher than other glaciers,accelerating its melting rate. |
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