Estmating Glacier Velocity And Monitoring Variation Of Typical Ice Shelves In Antarctic

The Antarctica is an important part of the cryosphere,and it has a complex interaction with the atmosphere and the ocean.It is an important source of power for the ocean current cycle and atmospheric cycle,and plays a role in regulating the global heat balance.97.6% of Antarctica is covered by ice and snow,and the area of the ice sheet and ice shelf is 1.36 × 107 km2,the ice volume is 3.01 × 107 km3,and the average ice thickness is 1 962 m.If all the melting will cause global sea level rise 58 m.In the context of global warming,the ice shelf on the edge of the Antarctic and the nearby ice sheets continue to melt and thinning,and the flowing velocity of outlet glaciers is also constantly increasing.The loss of the Antarctic ice sheet is higher than the income and the total ice volume are constantly decreasing,which is considered to be one of the causes of global sea level rise.Glacier flow velocity is one of the important parameters of the Antarctic continent.It can help understand the spatial distribution characteristics of flow velocity,quantitatively analyze the output quality of ice shelves,and fully understand the dynamic changes of local ice sheets and ice shelves,such as the occurrence of cracks and the impacts on ice sheets,etc.Having Used 3218 scene Sentinel-1 GRD data and offset tracking method to extract the Antarctic glacier velocity.Compared with SLC(Single Look Complex)data,the resolution reduced GRD(Ground Range Detected)data has the advantages of small data volume,high glacier velocity extraction efficiency,and small post-processing workload.After eliminating the errors,a total of 4.5 × 107 accurate velocity vectors were obtained,and the Antarctic velocity field with a resolution of 450 m was obtained by non-interpolation method,with a total coverage area of 8.17 × 106 km2.Error analysis from 2 aspect shows: 1)A total of 83 597 pixels are located in the area where bare rocks are distributed,with a standard deviation of 10.6 m·a-1.2)The average value of the difference from the MEa SUREs velocity product is 5.6 m·a-1,mainly concentrated between-60 ~ 60 m·a-1,accounting for 99.2% of the total pixels.Compared with previous studies,this paper developes new data source and proves that the reduced resolution GRD data is feasible in extracting the flow velocity of glaciers in a large scale,and has the advantages of high efficiency and high accuracy.At the same time,a new velocity mosaic method is proposed,which takes the velocity vector point as the basic unit and projects it into a grid with a size of 450 m according to the Antarctic spherical coordinates,and uses the median value as the velocity value.The velocity result updates the existing products,and as a supplement.A total of 73 glaciers and ice shelves were selected by basins,and the characteristics of glacier movement were analyzed by length,width,average flow velocity,maximum flow velocity,elevation drop and flow velocity along mainstream line: 1)gravity is the driving force of glacier movement,and the glacier moves along the hillslope,and the speed of movement continues to accelerate and reaches the maximum at the hillfoot.2)The speed of the glacier movement is related to the elevation drop.The elevation drops of glaciers with medium movement speed and above(> 500 m·a-1)is generally above 800 m.3)Along the mainstream line,the elevation drops rapidly in the ice sheet part,and in the ice shelf part it tends to be gentle,and the change of the glacier flow velocity is similar to the change of terrain.Seven typical ice shelves were selected,and Sentinel-1 data was used to extract the monthly glacier flow velocity in 2019 and analyze its movement variations.It is found that the flow speed of the ice shelf in each month is fluctuating,which is related to the degree of sea ice freezing,but not related to the season.The sea ice freezing will hinder the movement of the ice shelf by more than 8.7%,and the peak flow velocity occurs in the month that the sea ice has not been frozen.Seasonal change is not the main reason for the fluctuation in the degree of sea ice freezing.The degree of sea ice freezing in winter(June,July and August)may be the same as that in summer(December,January and February),meanwhile glacier flow velocity in winter could be close to that in summer,just as Ronne,Brunt,Jelbart Ice Shelf.Using ERS-1 & 2 and Sentinel-1 images to study the variations of the area of seven typical ice shelves from 1999 to 2019.The Pine Island Ice Shelf in the south west Antarctica has entered an active cracking period since 1999,with a total area loss of 1,074 km2 over past 20 years.The Larsen-C ice shelf in the Antarctic Peninsula experienced large-scale cracking in 2004-2009 and 2014-2019,which lost an area of 1 435 km2 and 5 664 km2.The rest of the ice shelves located in the south east Antarctica are stable compared to the ice shelves in the southwest Antarctica and the Antarctic Peninsula,and they get wider year by year.Among them,the Ronne Ice Shelf lost an area of 8 582 km2 in 1999-2004,but increased by an area of 8 569 km2 in 2004-2019,finally returning to the level of 1999.Amery,Brunt,Cook,and Jerbart ice shelves increased a total area of 3 785,4 597,1 312,and 879 km2 from 1999 to 2019 respectively.