Research On Ice Sheet Feature Extraction Of Lambert Glacier Drainage Basin, Antarctica Based On ICESat And Ice Radar Data

So far, because of the limitations of scientific cognition levels and technical conditions, the researches of the high-impact factors on dynamic mechanisms of ice sheet change are so weak that sea level rise projections still have great uncertainties. Therefore, in order to predict the result of sea level rise more accurately, the urgent requirement is to strengthen the observations of ice sheet from surface to interior, and to obtain high spatial and temporal resolutions and high precision data to provide observation supports and data base for the theoretical analysis and numerical simulation studies for ice sheet dynamic mechanisms.Lambert Glacier drainage basin is one of the key areas for the study of ice sheet mass balance effect on sea level. However, the current international observations of this basin still have many inadequacies. On the surface of the glacier basin, high spatial and temporal resolution distributions of mass changes are lacking, which cannot support intuitive understanding for the different regions of ice flow dynamics; at its bottom, the subglacial topography with sub-km resolution scale, which is great significance for the analysis of the different types of ice flow dynamic mechanisms, is lacking.Therefore, this paper extracts elevation changes with high spatial and temporal resolution on the surface of Lambert Glacier drainage basin using altimetry data to identify the regional characteristics of ice flow change. The feature extraction of subglacial topography with sub-km resolution scale mainly concentrates in two areas. One is the Dome A region which is the source of Lambert Glacier drainage basin, and the other is Zhongshan Station-Dome A transect in eastern basin. The main contents and conclusions include: (1) To extract the surface elevation change, based on the elimination of elevation differences of overlapping footprint pairs caused by the slope from adjacent operation periods of ICESat, we calculate the elevation change of overlapping footprint pairs. Then we use the inverse distance weighting, natural neighbor, radial basis functions and ANUDEM (Australian National University DEM) to interpolate the elevation change of each stage and chose the most accurate interpolation results as the elevation changes of the entire surface.The result shows that our method of eliminating the elevation difference is better, and the interpolation accuracy of ANUDEM is the highest. In the time scale, the elevation of Lambert Glacier drainage basin grows about0.002cm/a, and the acceleration of growth is slowing. Therefore, the mass of the basin is in balance. Except near the grounding lines with regions of elevation reduction exceeding2m/a, the elevation changes in most regions are less than1m/a. In the spatial scale, the elevation change has significant regional distribution characteristics. In the latitude direction, the elevation of downstream areas shows a decreasing trend and the reduced acceleration is increasing; the elevation of upstream areas increases0.84cm/a, but the acceleration of the growth is slowing. In the longitude direction, the elevations of the three major tributaries are in growth trends, and the Fisher tributary has the fastest growing, about1.09cm/a. However, the accelerations of growth in the three major tributaries elevation are also slowing, and Mellor tributary has the maximum extent of slowing. Combined with the ice flow data, the regions with elevation reduction exceeding1m/a are mainly in Lambert and Mellor tributaries, and the regions with velocity greater than100m/a of the two tributaries are affecting further200km of the inland region, while the corresponding region of Fisher tributary is only75km. This indicates the role of ice stream in Fisher tributary is less than the other two tributaries.(2) In order to extract the subglacial topography of Dome A region, we firstly create a semi-automatic method to extract the ice thickness of the transect from ice radar data. Then we interpolate the ice thickness and surface elevation of Dome A using a variety of methods, and choose the best accuracy results (ANUDEM obtained) as the ice thickness and surface elevation model. Finally, we combine the ice thickness with the surface elevation to produce the subglacial topography of Dome A region.The result shows the cross points with absolute thickness difference less than50m derived by semi-automatic method account for76%and less than100m account for92%, while the corresponding points derived by artificial digital method are61%and89%. And compared with the international AGAP (Antarctica’s Gamburtsev Province) data, the consistency of semi-automatic method is also better than artificial digital method. This indicates the consistency and accuracy of semi-automatic method have improved than previous methods. Using AGAP data to compare the ice thickness model derived by us with the one of previous method, we found the mean thickness difference of our result is only3.5m, which is far superior to artificial digital method (17.7m). Therefore, the accuracy of the new three-dimensional subglacial topography of Dome A is the best, which will play an important role in the regional ice sheet model simulation, the understanding of ice flow dynamics and the evolution of the ice sheet. Based on this method, we create datasets for Elmer/Ice model running in Dome A for the research on the basal temperature of ice and estimate the relationship between the depth and age of the ice layer.(3) For the extraction of the subglacial topography of the Zhongshan Station-Dome A transect, we calculate two-parameter roughness index in the sliding window using the Fast Fourier Transform to quantitatively describe the abnormal elevation change of the ice-bedrock interface. In the extraction process, because the Fast Fourier Transform can transform ice-rock interface into a sum of several various wavelength periodically corrugated surfaces, besides obtaining the total ice-rock interface roughness, we also divide the ice-rock interface into three scales:long wavelength (greater than1680m), medium wavelength (840-1680m) and short wavelength (420-840m), and the analyzed the distribution of roughness with different wavelengths scales.The ice-rock interface includes two main types in the window scale which this paper used:both of the ζ and η values are small relating to the ice-rock interface with small elevation fluctuation and fast frequency of horizontal change; both of the ζ and η values are large relating to the ice-rock interface with high elevation fluctuation and slow frequency of horizontal change. The result indicates that the vertical fluctuation of ice-rock interface in the south side transect of Lambert tributary is generally greater than the north side, and compared with the high peaks in the north side, the slopes of peaks in the south side are also high. By analyzing the roughness among the different wavelength scales, we find long wavelength scale terrain is the main characteristics for the ice-rock interface of the entire transect, but there are also some special terrain areas. For example, the analysis finds that short wavelength terrain is the main feature in the areas with elevation fluctuation less than200m in the two ends of the transect in the north side of Lambert tributary. The medium wavelength is the main feature in some parts of the transect in the south side of Lambert tributary, and the short wavelength topography has been eroded.