Analysis Of Remote Sensing Temporal And Spatial Variation Of Glacier Surface Elevation In Mountainous Asia

In the context of global warming,Asian mountain glaciers,as an important source of river recharge in arid areas of Asia and Western China,provide important freshwater resources for the surrounding areas.Glacier monitoring is of great significance for a comprehensive understanding of the relationship between mountain glaciers and climate change in Asia and the early warning of secondary glacial disasters.The development of remote sensing technology provides abundant data resources for glacier research,which makes it possible to understand the law of large-scale glacier change.Among them,satellite laser altimetry technology is one of the main means of glacier monitoring.ICESat data laser footprints are distributed sparsely and unevenly in middle and low latitudes.In order to realize the monitoring of glacier surface elevation change,two problems need to be solved.Question 1:the laser foot of ICESat data is affected by factors such as cloud and terrain,and the error is large;Question 2:ICESat has poor temporal and spatial coherence due to the non repetition of satellite orbit and sparse distribution of laser feet.In view of the above problems,this paper establishes the point cloud denoising and precision optimization algorithm in glacier area based on icesat-1and icesat-2 experimental data,and constructs the multi-scale analysis model of temporal and spatial change of surface elevation in glacier area,so as to obtain the change of glacier elevation,and improve and supplement the existing laser satellite data processing and analysis methods.Analyze the results of glacier elevation changes,understand the temporal and spatial changes of glaciers in various regions of Asia,and realize glacier time series monitoring.Main research contents and results:（1）Aiming at the denoising and accuracy optimization of ICESat data point cloud.In this paper,the normal distribution test of icesat-1 data is carried out.According to the results of normal distribution,the multiple standard deviation away from the average value is used to eliminate the error;Icesat-2 data reserves the data with the difference within±100m from the benchmark DEM.Two different denoising methods are adopted,which are mainly based on the difference of the accuracy and sampling density of the two data.Using the denoised data and taking the benchmark DEM as the intermediate variable,a polynomial fitting function model is established to obtain the fitting function between DEM elevation and ICESat elevation.For the studied data,only high-precision data are retained to ensure the reliability of the fitting function and the research results.According to the fitting effect and parameter comparison before and after denoising,the fitting effect is significantly improved.（2）Aiming at the problem of poor temporal and spatial coherence of point cloud data in glacier area.Based on the fitting function between DEM elevation and ICESat elevation obtained above,this paper establishes a multi-scale spatial-temporal variation analysis model of surface elevation in glacier area.The datum DEM elevation data is substituted into the corresponding polynomial fitting function to obtain the temporal changes of glacier height from 2003 to 2009 and from December 2018 to may 2021.The variation trend of glacier elevation in this area is as follows:From 2003 to 2009,the surface elevation of glaciers in high mountain areas of Asia decreased within 10m,and the change of glacier elevation showed obvious regional differences.From 2018 to 2021,the change rate of glacier elevation in the whole Asian region is-0.59m·a^-1,The change rates of glacier elevation in Tienshan,Kunlun,Karakoram,Himalaya and Southeast Qinghai Tibet Plateau are-0.72m·a^-1,-0.84m·a^-1,0.04m·a^-1,-0.48m·a^-1and-0.68m·a^-1respectively.（3）Based on polynomial fitting functions obtained from icesat-1 and icesat-2data.Obtain the variation of glacier surface elevation in different altitudes,slopes and slope directions in various regions from 2000 to 2021.Analyze the variation law of glacier surface elevation in different altitude,slope and slope direction.Although there are differences between regions,the overall performance is that glaciers in low altitude areas are mainly ablated,and the amount of ablation is the largest.With the increase of altitude,the amount of glacier melting decreases,and even the elevation increases in high-altitude areas.The slope data show that the variation of glaciers in the slope range of about 0°～30°decreases with the increase of slope;Within the slope range of30°～50°,the amount of glacier ablation increases,but within the range of glaciers with a slope greater than 50°,the amount of glacier ablation decreases with the increase of slope.However,due to the large slope,the slope in this area is steep and prone to avalanche or ice avalanche,resulting in high-range thinning of the surface.Slope direction analysis shows that the glacier shows an ablation trend in 8 slope directions,but the ablation degree is different.In most areas,glaciers in the north direction melt slowly,while glaciers in the East and south directions melt faster.The relationship between temperature,precipitation and elevation variation is as follows:The glacier elevation increases with the increase of precipitation,and there is a positive correlation between them;The glacier elevation shows a thinning trend with the increase of temperature,and the two show a negative correlation.There are 23 figures,11 tables and72 references.