Ice shelf breakups account for most mass loss from the Antarctic Ice Sheet as the consequence of the propagation of crevasses(or rift)in response to stress.Thus there is a pressing need for detecting crevasses’location and depth,to understand the mechanism of calving processes.This paper presents a method of crevasse detection using the ICESat-1/GLAS data.A case study was taken at the Amery Ice Shelf of Antarctica to verify the accuracy of geo-location and depth of crevasses detected.Moreover,based on the limited crevasse points,we developed a method to detect the peak stress points which can be used to track the location of the crack tips and to identify the possible high-risk area where an ice shelf begins to break up.The spatial and temporal distribution of crevasse depth and the spatial distribution of peak stress points of the Amery Ice Shelf were analyzed through 132 tracks in 16 campaign periods of ICESat-1/GLAS between 2003 and 2008.The results showed that the depth of the detected crevasse points ranged from 2 to 31.7 m,which were above the sea level;the crevasse that advected downstream to the front edge of an ice shelf has little possibility to directly result in breakups because the crevasse depth did not show any increasing trend over time;the local stress concentration is distributed mainly in the suture zones on the ice shelves.
LIU YanCHENG XiaoHUI FengMingWANG XianWeiWANG FangCHENG Cheng
Digital Elevation Models(DEMs)for Antarctica are critical datasets for general circulation models,change analysis of ice sheet dynamics and logistical planning of field expeditions.To date,there are five different DEMs covering all of Antarctica,all of which were derived from satellite radar or laser altimetry data in combination with ground data.Since the margins of ice sheets are highly dynamic in space and time,DEMs of Antarctica should be updated frequently as new data become available.We used Radar Altimeter(RA-2)data from Envisat and laser altimeter(GLAS)data from ICESat to create an up-to-date DEM of Antarctica with high accuracy and precision of elevation measurement.In this paper,these two different sources of satellite altimeter data from 2003 to 2009 were integrated to generate a DEM for the entire continent of Antarctica.We applied five different quality judgment rules to filter unreliable ICESat/GLAS data;as a result,8.36%of the data were filtered out.A relative correction method based on speckle geometry intersection was used to correct Envisat RA-2 elevations to ICESat/GLAS.The data were interpolated to a regu-lar 1000 m polar stereographic grid using ordinary Kriging after semi-variance analysis.The accuracy of the final DEM was assessed through a comparison with two airborne LiDAR datasets,a field GPS strip from China's Zhongshan Station to Dome A and the most recently published DEM.The comparison result shows that the error of the new DEM is from 32.1 m to 27.84 m,and the distribution of errors depends on the surface slope.The new DEM shows an obvious improvement on steep slopes,including the quickly changing ice sheet margin areas.
