Monitoring Glacier Changes In The Puruogangri Ice Field During 1975-2021 Based On Multisource Remote Sensing Observations

Under the background of climate warming,glaciers in most areas of the Tibetan Plateau have experienced accelerated retreat,and are highly heterogeneous in spatial and temporal scales.The rate of glacier change is inconsistent,especially within the Tibetan Plateau.As the largest ice field in the central part of the Tibetan Plateau,mon-itoring its long-term changes in glacier area,mass balance and surface velocity of the Puruogangri Ice Field can effectively reflect the overall trend of glacier changes in the Tibetan Plateau.However,relevant studies based on satellite data mainly focus on2000-2016,while long-term and multi-temporal observations before 2000 and in recent years are still under investigation.Therefore,the main research of this paper is as fol-lows:（1）Using Landsat and KH-9 optical images,band ratio method and visual inter-pretation method were used to extract the glacial boundaries of the Puruogangri Ice Field from 1975 to 2021,and estimate its area changes.The results show that the total area of the Puruogangri Ice Field has decreased from 427.44±12.43 km² in 1975 to387.87±11.02 km² in 2021,with a shrinkage rate of-0.86 km² a^-1.The distribution of glacier area with altitude is in accordance with the characteristics of normal distribution.The glacier area basically remains unchanged when the altitude is above 5900 m.（2）Using KH-9 DEM,SRTM DEM,Copernicus DEM and ZY-3 DEMs,geodetic method was used to estimate the glacier elevation change and mass balance of the Puru-ogangri Ice Field during 1975-2021.The results show that,the Puruogangri Ice Field has been obviously thinning since 1975,and the whole glacier is in a state of mass loss,especially in the past 20 years.The ice field has been in a state of ablation during 1975-2000,and the trend is more pronounced during 2000-2021,with an average mass bal-ance of-0.23±0.02 m w.e.a^-1 and-0.29±0.02 m w.e.a^-1,respectively.The ice field is in a stable state with a mass balance of-0.04±0.01 m w.e.a^-1 during 2000-2012 and-0.17±0.01 m w.e.a^-1 for the period 2012-2021,indicating significant ablation in the last 10 years.（3）Using Landsat OLI images from 2014 to 2018,COSI-Corr software was used to obtain the interannual velocity distribution of the Puruogangri Ice Field based on the optical image cross-correlation method.The results show that,the glacier status was relatively stable from 2014 to 2018,and the glacier surface velocity was basically con-stant.The velocity of large glaciers is faster,and the results are more obvious at the glacier terminus.The surface velocity on the northeast slope of the ice field is greater than that on the southwest slope,showing significant spatial differences.（4）The effects of glacier morphological factors as well as climate factors on glac-ier changes were discussed.The results show that the surging or advancing glaciers could lead to the increase of glacier area,especially the surging glacier,but have little effect on mass balance.Temperature and precipitation are the main factors affecting the glacier change,and the glacier changes in this region are more sensitive to the increase in temperature.The larger the glacier is,the more stable it is.The smaller the area is,the more obvious the glacier retreat and melt.When the altitude is lower,it is more susceptible to climate change,and the higher altitude areas have less change.