| Glaciers are recognized as essential indicators of climate change,and great changes associated with global warming have been occurring in mountain glaciers.Glacier surface temperature(GST),which is strongly correlated with the ablation rate,is extremely sensitive to thermal processes related to both climatic and ice surface conditions.GST has,therefore,been used for glacier mass balance and runoff modelling and debris thickness estimations,highlighting the long-term dynamics of climatic conditions and changes of glacier surface properties.To date,a large number of algorithms that can be used in retrieving surface temperature have been developed,including the mono-window algorithms,split-window algorithms,and multichannel algorithms.A variety of remote sensing retrieval studies based on each sensor type have been carried out on land surface temperature(LST),sea surface temperature(SST),and lake surface temperature(La ST),which have been applied in different regions.Unfortunately,as for glaciers,limited investigation has been conducted on GST due to the remote locations of glaciers and the difficulty of determining ice surface emissivity.According to the literature,previous studies on GST,however,are inadequate in terms of time series investigations and mountain glacier surface temperature retrieval,and most of the studies concerning GST have concentrated on the polar regions,employing coarse spatial resolutions.Furthermore,the numbers of images in these studies are so few that the temporal variation of the GST is hard to obtain.To address this shortcoming,this study aims to employ the modified mono-window algorithm to retrieve the surface temperature from Landsat5 TM Band6 data combined with the Landsat8 TIRS Band10 data for the glaciers in Mount Gongga,southeastern Tibetan Plateau,from 1990 to 2018.For this algorithm,three parameters were needed(ground emissivity,atmospheric transmittance,and effective mean atmospheric temperature).Furthermore,the debris thickness around the glaciers in Mount Gongga was calculated based on the GST retrieval products,and the variations of debris cover extent coupled with debris thickness between 1990 and2019 were analyzed and discussed using these results.The main research conclusions include the following aspects:Firstly,the remote-sensing-retrieved temperature distribution shows that surface temperatures of all the glaciers in Mount Gongga decrease with increasing elevation,in which the mean temperature gradient of Hailuogou Glacier is about-6.1?/1000m,slightly lower than the air temperature(-6.1?/1000 m),the mean temperature gradient of Mozigou Glacier is about-7.2?/1000 m,the mean temperature gradient of Yanzigou Glacier is about-10.3?/1000 m,the mean temperature gradient of Nanmenguangou Glacier is about-10.6?/1000 m,the mean temperature gradient of Dagongba Glacier is about-11.4?/1000 m,and the mean temperature gradient of Xiaogongba Glacier is about-12.2?/1000 m.Secondly,GSTs of the six typical glaciers in Mount Gongga change in a seasonal way and the average temperatures show a clear seasonal fluctuation,GSTs in summer are higher than in winter.Additionally,average temperatures in the six typical glaciers show an increasing trend between 1990 and 2018,however the increase in the Hailuogou Glacier and Mozigou Glacier is more significant.The average temperature of debris-cover area is higher than that of the debris-free area.There is no obvious trend in the 0?isothermal line of each glacier,but it fluctuates within 4000 to 5000 m.Thirdly,glacier debris cover expansion and ice surface darkening,topography,and climate are the major factors in the spatial-temporal variation of GSTs.Finally,debris coverage of glaciers in Mount Gongga increases 43.824 km~2,wherein Hailuogou Glacier increases 2.606 km~2,Mozigou Glacier increases 1.959km~2,Yanzigou Glacier increases 1.243 km~2,Dagongba Glacier increases 0.896 km~2,Xiaogongba Glacier increases 0.509 km~2and Nanmenguangou Glacier increases2.264 km~2,and annual increased rates are 3.2%,11.1%,1.5%,0.9%,1.0%and 6.5%respectively.And,their debris layers thickened by an average of 5.2 cm?3.1 cm?3.7cm?6.8 cm?7.3 cm and 13.1 cm respectively.Of note,glaciers on western slope have lower annual increased rates and the terminal retreat rate,while higher debris coverage proportion than that on eastern slope. |
PDF Full Text Request