Application Of Glacier Inventory And Airborne LiDAR Point Cloud Data In Glacier Change

Glacier is major part of the cryosphere on the earth-atmosphere climate system,Glacier change is direct reflection of the energy-mass balance change among the spheres,and is considered as a reliable indicator of climate change.Affected by climate warming,historically unprecedented global glacier decline has occurred in the early 21st century.Glacier mass balance,as a key parameter for quantitative index of glacier melting,clearly represents the mass budget on the glacier surface,due to its direct and undelayed response to local atmospheric conditions.At present,the assessment of glacier mass balance is mainly based on glaciological observation method and geodetic observation method,where precise glacier spatial extent is the basis for accurate measurement of glacier mass balance.At first,we used the newly Randolph Glacier Inventory(RGI6.0)compiled in 2017 to measure the distribution and recent change of global mountain glacier resources.Secondly,macro-scale glacier mass balance assessment needs high-resolution DEM products to support,and the airborne three-dimensional laser scanning technology is best choice for high-precision point cloud data acquisition for now.However,due to the high cost of airborne laser scanning,this study only takes the laser point cloud data of Hulugou basin in Qilian Mountains of China acquired by Heihe Watershed Allied Telemetry Experimental Research(HiWATER)in 2012 as research objects to discuss its application in glacier mass balance monitoring.Therefore,the research work on glacier change has been carried out at two different spatial scales:global scale and basin scale,focusing on the glacier mass balance,which is the core link of glaciers'response to climate change.The following conclusions are obtained:(1)Based on the Randolph Glacier Inventory(RGI6.0)released in 2017,Contemporary distribution characteristics of global mountain glacier resources were systematically illustrated.There are 215,547 mountain glaciers in the world,with a total area of 705739±4.2%km~2,distributed in 19 first-order glacier regions.The number and area of glaciers are mainly those with area class below 1 km~2(79.15%)and those with area class above 100 km~2(54.87%),respectively.Influenced by the huge sizes of Antarctica and Sub Antarctic Islands,the elevation curve of glacier area along with altitude distribution skews to be in low altitude band on the global scale,about 80%of global glacier area is distributed below 2000 m above sea level,and the maximum area height band is only about 300 m.The number and area of glaciers with an average slope of less than 30 degrees reached 76.6%and 97.8%of the global total.There was a significant difference between the glaciers orientation for different hemisphere,the area of glaciers in the northern hemisphere was mainly N-oriented,while that in the southern hemisphere was mainly S-oriented.(2)Based on the IPCC Fifth Assessment Report,the global mountain glacierized area retreat has been preliminarily quantified with reference to recent glacier change literatures.In the past 50 years,mountain glacierized area have experienced a strong retreat worldwide.The area-weighted shrinking rate of global glacier was 11.3%and the interpolated annual percentage of area changes(APAC)was 0.35%since 1960.There is a significant regional difference in the magnitude of the APAC,with a difference of more than 30 times between the fastest one in Low Latitudes area(2.28%)and the slowest one in Arctic Canada North area(0.07%).It has been proved that the spatial structure stability of mountain glaciers is very fragile by fractal theory,and it is very likely that the glaciers will continue to retreat to achieve balance with the current climate for a long time in the future.(3)Based on the airborne LiDAR point cloud data measured by airborne remote sensing using Y-12 aircraft in 2012,the calculation and error assessment of glacier mass balance were completed by geodetic observation method in Hulugou basin on the basis of LIDAR DEM generation,spatial co-registration and vertical resolution correction of SRTM DEM.Glacier surface elevation decreased by an average of 9.55m from 2000 to 2012,corresponding glacier cumulative mass balance was-8.12±1.59 m w.e.by way of density conversion,which is about(860.72±168.54)×10~4 m~3water equivalents.It is found that the difference is only 0.1 m w.e.after verification with the measured mass balance in Shiyi Glacier,which confirms the high accuracy advantage of airborne LiDAR point cloud data in the study of glacier mass balance.By analyzing the monitoring data of adjacent meteorological stations,it is found that the continuous increase of temperature since 1960s,especially the accelerated increase after 2000 and the decrease of precipitation in the same period are the main causes of glacier retreat in Hulugou basin.This paper provides new data support and methodological reference for related research by exploring the application of Glacier Inventory and airborne LiDAR point cloud data in glacier change.However,owing to the lack of multiple global glacier inventories for comparison,it was not yet possible to make an authoritative assessment of global mountain glacier change.Therefore,more scientific measurement of global mountain glacier changes through summarizing the research results of typical glacier regions will remain the focus of this study.On the other hand,considering the high cost of acquiring airborne LiDAR point cloud data,the terrestrial three-dimensional laser scanning and high-precision satellite-borne microwave radar data will become the main data sources for getting glacier mass balance by geodetic observation method in the future.Although remote sensing technology can obtain accurate understanding of the results of glacier change,but it cannot fully reveal the internal mechanism from the natural response of glacier to climate change.The combination of remote sensing method and energy-mass balance model is the research direction of this paper in the future.