| Glacier is one natural ice body existing on the surface of the polar region or high mountains for many years and moving along the earth surface.Glacier change is closely bound with the global climate,ecological environment and human social development.Against the backdrop of global warming,the glacier as one sensitive factor of climate change has played an important role in the studying climate change,understanding the interactive mechanism of climate and glacier change.Multi-source remote sensing data find their effective application in wide-range and long-term glacier change monitoring and in particular make the study of glacier zone in bad natural conditions possible.Located in the Qinghai-Tibet Plateau and characterized by the most apparent increase of mean temperature in summer,the Yigong Zangbu Basin is among Chinese typical mountain glacier areas.In this area the climate fluctuation and ecological imbalance caused by glacier shrinkage are especially striking.However,restricted by many factors and conditions,the Yigong Zangbu Basin has been constantly the data shortage section of glacier inventory.Studying the form evolution as well as mass balance in this basin is conducting one research of particularity based on the universality.Glacier movement and glacier thawing on the surface transmit mass accumulation at high elevations to low-elevation ecological circle,forming the mass circulation between glacier,and basin climate,ecologic system and hydrography.The form changes of glacier(area and elevation changes)and bottom mass exchange(glacier flowing)are the major factor influencing glacier matter balance while glacier,runoff and the atmosphere are mutually interactive driving force influencing the interior local climate system.This paper focuses on the Yigong Zangbu Basin' s glacier change and mass balance,employing multi-source remote sensing data system to complete the monitoring work of glacier area,surface flowing velocity and elevations.Based on this,by combining with such data as temperature,the precipitation amount and other data,this paper analyzes glacier change's response to climate,exploring the relationship between glacier mass transmitting and the geometric form of the glacier and predicts the glacier's changing tendency in the future.The major research results are as follows:1.The research has extracted the data of the Yigong Zangbu Basin area and completes the second Chinese glacier inventory;it employs three SAR(Synthetic Aperture Radar)data sources including ENVISAT ASAR,ALOS PALSAR,Sentinel-1 A,making use of incoherence of the glacier between the SAR interference pair to make sure the glacier and non-glacier zones in the year of 2003,2007,2010,2015;then it combines the Landsat video to set the elevation threshold value and extract the glacier boundary data with more than 82%accuracy,obtaining the result of glacier monitoring.The Yigong Zangbu Basin presents a concentrated distribution of glaciers whose mean elevation is more than 5200 meters.The glacier coverage from 2013 to 2015 presents the tendency of“small increase and big decrease",namely from 23.5%to 27.9%to 13.8%,and the shrinking speed rate is 0.8%/aIn the three major glacier accumulation areas(Part1?Part2?Part3)of the Yigong Zangbu Basin,Part 1 is mainly mountain ice cap,hanging glacier,ice bucket glacier which cover small areas and present an independent distribution,showing the most conspicuous recession;Part 2 is mainly the glacier tongue whose elevations present continuous changes,showing the recession mainly in the mass transmitting part ranging from glacial amphitheater to the end of the glacier tongue;Part 3 is mainly the large compound valley glacier which shows conspicuous recession but has relatively complete geometric forms,showing the glacier thawing major in large-slope mountain surface.2.The research has extracted the data of the Yigong Zangbu Basin's surface speed.Based on the feature tracking theory,the research estimates the glacier surface speed of the corresponding year in the SAR video pair and makes a weighted estimation of ELA(Equilibrium Line Altitude)with AAR(Accumulation Area Ratio).According to the research result,the Sentinel-1A video pair has the first highest accuracy of registration,ALOS PALSAR has the second highest accuracy and ENVISAT ASAR has the third highest accuracy.All of those three video pairs can meet the demand of counting accuracy.In the summer of 2003,2007,2010 and 2015,the glacier surface displacement rate is respectively 0-464.6m/a?0-515.4m/a?0-492m/a?0-447.5m/a.The change of surface form drives glacier movement and glacier flowing speed of different types differs greatly:the hanging glacier and ice bucket glacier accumulated by glacial amphitheater have slow flowing speed while the valley glacier and large compound valley glacier have fast flowing speed and show conspicuous speed peak values.The research has extracted data of the watershed ridge line by using DEM,and has analyzed the area change,surface velocity and ELA of 19 glaciers according to glacier type.Among them,the distribution of the flowing velocity is similar because of the same data source in 2003 and 2010.In 2007,the glacier is more stable,with obvious high velocity area and large low-velocity areas.In 2015,the glacier coverage decreases sharply,and the surface velocity is the most obvious,The ELA of Part1 is 5,860m,the velocity of Kaja glacier,G093563E30502N glacier,Yali Lanong glacier,and the tower glacier,the average velocity is concentrated in 206?208mla;the ELA in part is about 5,730m,G093579E30315N glacier,G093642E30319N glacier,Ga luogong glacier,Rongwa glacier and G093951E30329N glacier.The velocity is concentrated in 0.9?428.5m/a;the ELA of part1 is 5690m,Dangwusemeng glacier,Rongpu glacier,Xialiepu glacier,Tayanong glacier,Le pu glacier,glacier,Xiaqu glacier,G094591E30498N glacier,Yiqing glacier,Ruoguo glacier,the velocity is concentrated in 0?515.7m/a,Part3 is the largest glacier accumulation area in the Yigong Zangbu Basin,and there is a significant slope difference in the glacier surface velocity distribution.The surface mean velocity increases with the decrease of the glacier area,and the ablation divides the glacier into smaller independent units.The change of the internal force balance is the cause of the redistribution of the velocity.3.The research has estimated the surface elevation change of the Yigong Zangbu Basin' s glaciers.By using two kinds of satellite altimeter data,namely ICESat and Cryo Sat-2 to do comparison experiment,referencing the ellipsoid system transformation,effectively combing GLAS14 and L2I to carry on glacier surface elevation change monitoring.Considering the data of the spatial distribution and temporal continuity,the elevation change monitoring can be divided into 3 different monitoring units(cirque/hanging glacier,valley glaciers and double valley glaciers).After strictly excluding outliers,the research takes SRTM DEM as the reference plane to calculate each year's elevation measurement value(2003-2008 ICEsat/GLAS 14,2009-2015 segment for years CryoSat-2/L2I)to fit the change between 2003-2015 Yigong Zangbo valley glacier surface elevation trend.Cirque/hanging glaciers in 2003-2015 have rates of-0.57m/a and-0.72m/a;valley glaciers in 2004-2015 show the state of growth and have rates of 0.61m/a and 0.11m/a;Glacier community which is made up by some double valley glaciers show the state of retreat and have rates of-0.21m/a and-2.22m/a.The undualatory result of Cryosat-2 is obviously higher than ICESat.In addition to the inherent error of atmospheric refraction,system noise,solid tide glacier elevation calculation of surface slope as well as roughness and the algorithm design are the main source of error in the altimetry data of local glacier elevation measuring data.4.The increase of temperature has a significant effect on glacier retreat.Through the analysis of the NCEP/NCAR monthly mean temperature data,it is found that the annual average temperature in the whole Qinghai-Tibeta Plateau is rising,and the average temperature of the glacier melting period in June-September is also rising,and the Himalayas to the Hengduan Mountains are more obvious.The monthly mean precipitation data of GPCP show that although the precipitation in the southeast of Qinghai-Tibet plateau is increasing,the precipitation in the period of ice accumulation is significantly reduced from November to February.There is negative coherence between the surface elevation and the temperature in the smallest ice cirque/hanging glaciers,and large compound valley with largest areas of the Yigong Zangbu Basin.The surface elevation of valley glacier is positively related to the precipitation in the accumulation period.The three types of glacier in the Yigong Zangbu Basin show different retreating models:the retreat of small glacier(cirque/hanging glacier)is the uplift of material balance line and the decrease of glacier surface elevation;The medium glacier(valley glacier)is mainly characterized by glacier tongue change,the glacier tongue fracture will change the glacier form,leading to the evolution of the valley glacier to small glacier,and the glacier tongue retreat changes the material transport rate.The surface elevation of valley glacier is affected by the winter rainfall in the upstream accumulation area.Large glaciers(double valley glaciers)show the decreasing area in its central accumulated area and divided into smaller separate glaciers,which is the main retreat mode.The mountain glacier area in tribute watershed is one of the most obvious regions of glacier retreat in China.The glacier zone of the Yigong Zangbu Basin is one of the most conspicuous glacier retreating areas in China.In conclusion,the increase of temperature is the biggest cause of glacier change in the Yigong Zangbu Basin,and the increased temperature can change the form of glaciers,cause continuous decrease of the surface elevation and increase the surface flowing speed.By observing the different remote sensing images in different years,it is found that the smaller and more independent cirque glacial/hanging glaciers in the basin is getting faster and faster,and the future will become the first glacial type in the tribute basin.While the valley glacier is affected by the gentle precipitation,the coexistence of the two forms of the growth and retreat of glacier tongue is the characteristics of this type of glacier activity.Although the large compound valley glacier is still relatively stable,and is more likey to be divided into more smaller glacier unit,namely,the valley glacier,the cirque glacier,the cirque valley glacier and the hanging glacier.Because of the appearance of the inner ridge line,the accumulation area is divided,and the accumulation area will be further reduced.Although the mountain glacier has experienced different time scales in the local temperature fluctuation since 2003,the overall climate change in the southeast of Qinghai-Tibet Plateau is developing towards the trend of unfavorable glacier growth. |
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