Estimation Of Glacier Velocity Over Tibetan Plateau

The Tibetan Plateau is the largest development center of mountain glaciers on Earth in addition to the Antarctica and Arctic regions,including the Hengduan Mountains,Southeast Tibet,the Himalayas,the Hindu Kush region,the Palmer Mountains,the Karakoram Mountains,and the West Kunlun Mountains,East Kunlun Mountain,Qilian Mountain,Inner Tibet area and so on.The glacier distribution and reserves of the Tibetan Plateau are so extensive that it is a huge high mountain solid reservoir,which is not only an important water resource in the highland area,but also maintains the plateau's environmental and ecological balance.Moreover,it is sensitive to record the change of climate and environment in the region,and also has obvious influence and response to the climate change in the Northern Hemisphere and the whole world.The distribution and change of glacier movement are the result and embodiment of climate and its change.Therefore,it is of great significance to estimate the glacier velocity and its variation in the Tibetan Plateau for exploring the change of water resources in the plateau and the climate change in the Tibetan Plateau and the whole world.Fast estimation of glacier velocity using remote sensing data is a convenient and efficient method for obtaining ice velocity.Because the Tibetan Plateau is rich in water vapor resources,a large number of clouds covers the sky all the year round,so the optical remote sensing data is limited,and there is a large amount of cloud cover on the image,which cannot be used to extract the characteristics of glaciers.Without the restrictions of cloud and rain,the synthetic aperture radar data,which can obtain ground information all the time,can be used to estimate the velocity of glaciers in the Tibetan Plateau.Using the Sentinel-1 radar data from September 2017 to November 2018 and the auxiliary data SRTM,using the migration tracking method,the glacier velocity of the ten largest mountains on the Tibetan Plateau in 2017 and seasonal variation of flow velocity of 15 typical glaciers in Tibetan Plateau from November 2017 to November 2018 are estimated.The effects of topography and climate on glacier velocity over Tibetan Plateau are analyzed,and the distribution and variation of glacier velocity over Tibetan Plateau are analyzed qualitatively according to the climatic spatial data of Tibetan Plateau(air temperature,precipitation,etc.).The mean glacier velocity over the Tibetan Plateau in 2017 is estimated by using the Sentinel-1 data of 36 days in the stable period of glacial movement in 2017.The results show that there are some differences in the glacier velocity in the ten mountains of the Tibetan Plateau.There are a large number of marine glaciers in Hengduan Mountains and southeast Tibet mountain,and the region has more annual precipitation and higher annual average temperature,and glaciers supplies are adequate,and glacier is melting intensely,so the region has a rapid glacier movement.The Himalayas is the most rugged region on the Tibetan Plateau.Due to climate,Himalayan glaciers flow less than the Hengduan Mountains and the southeastern Tibetan mountains,but due to the differences in precipitation and temperature on the south and north slopes,the Himalayan glaciers are less rapid than the Hengduan Mountains and the southeastern Tibetan mountains.Glaciers move faster on the southern slope than on the northern slope.The velocity of glaciers in the Hindu Kush and Pamir regions are greater than that in the Himalayas.Among them,the glaciers in the Hindu Kush region are mainly concentrated in the Hindu Kush Mountains,and a small number of large glaciers develop in the Pamir Mountains,the largest of which is the Fedchenko Glacier,and the annual flow rate can reach 300 m/yr.Karakoram Mountain is a concentrated area of large glacier development.The glacier has obvious and continuous glacier movement,and the glacier velocity is large.The maximum velocity of glacier can reach 200?500m/yr,but the velocity of glacier in Karakoram mountain is different spatially.The glacier movement in the western and middle parts of the Karakoram Mountains are faster than that in the eastern part,in which the glacier velocity in the western part is the largest and the velocity in the eastern part is the smallest.Due to the low temperature of the West Kunlun Mountains,there are large continental-type glaciers with a wide range of ice-tongue regions.But the terrain of the West Kunlun Mountains is gentle,and for both of these reasons,the glacier movement of the West Kunlun Mountain is not fast,and the annual flow rate of the ice-tongue part is below 100 m/yr.The glaciers in the Eastern Kunlun Mountains,Qilian Mountains and Inner Tibet are scattered in small scale and the glaciers move slowly.The annual flow velocity of glaciers in the ice tongue region is about several tens of meters,which is smaller than that of other mountains in the Tibetan Plateau.We have calculated the mean error of glacier velocity over the Tibetan Plateau in 2017.The average error is less than 10 m/yr,but the error of glaciers with smaller mean velocity is larger and the percentage of error is relatively high.In order to study the seasonal variation of glacier velocity,we analyzed the seasonal variation of 15 typical glaciers in 10 mountains of the Tibetan Plateau by using Sentinel-1 from November 2017 to November 2018.There are different seasonal variations in the velocity of the 15 glaciers,basically,the glaciers move faster from April 2018 to August 2018,and there are two characteristics of the glacier season:one is that the glaciers move more quickly and extend to the lower part of the ice tongue;The other is the intense fluctuations in glacier movement.The seasonal variation of the continuous glaciers is more obvious,such as the Baltoro glacier in Karakoram Mountains,which has obvious motion,and the larger the velocity of the season,the more obvious movement of the ice tongue part.At other times,glaciers are in a more stable state.Finally,we discussed the factors affecting glacier velocity,such as topography,climate and so on.In the aspect of topographic factors,different scholars have put forward different views on the influence of local topography,slope and aspect on glacier movement.At the same time,other scholars have proposed that the different angles of the tributaries and main streams of glaciers will also have different effects on the velocity of glacier mainstream.At the same time,the precipitation and air temperature of different mountains are discussed in time and space based on the climatic spatial climate set simulated by the Tibetan Plateau from 1991 to 2020.It is proved that the velocity distribution of glaciers in different mountains is reasonable and their important effects on the velocity of glaciers.