Multi-fold technology is widely applied in seismic exploration as a method of enhancing useful signals and suppressing noise interference to greatly increase the signal to noise ratio （S/N）. The authors introduce it to ground-penetrating radar （GPR） surveys and compare the experimental results to the conventional profiling method to demonstrate the feasibility and advantages of the technique for GPR exploration. Based on the experimental data, the authors summarize the GPR wave propagation rules and the parameters of multi- fold acquisition and processing. It is proven to be a useful attempt to enrich the GPR survey technology.
Wang Bangbing Tian Gang Sun Bo Guo JinxueZhang Xiangpei
During the 24th Chinese National Antarctic Research Expedition(CHINARE 24,2007/08),a ground-based ice radar was used to survey ice thickness and subglacial topography along the 1170 km traverse between Zhongshan and Dome A in East Antarctic ice sheet(EAIS).Ice-bedrock interface was detected along 82%of the traverse and data was collected at a horizontal resolution of <5.6 m.The data was processed to produce curves of ice thickness distribution and subglacial topography along the traverse.The results indicate that,along the traverse,the average ice thickness is 2037 m,smaller than the average ice thickness in EAIS;the thickest ice is at 730 km,and the thinnest ice(891 m)is at the edge of the ice sheet,but the slightly larger ice thickness(1078 m) in inland appears at 1020 km;the average subglacial topography elevation is 728 m,greatly larger than the average value in EAIS, and the largest elevation reaches up to 2650 m at 1034 km.The lowest terrain is located at 765 km.In further inland of 900?1170 km,the subglacial topography is relatively high due to the existence of the Gamburtsev Subglacial Mountains in the region.Generally,the influence of subglacial topography on ice surface is not significant,except at 900 km where great rise of subglacial topography causes evident uplift of ice surface.Where ice-bedrock interface was detected,the frequent and strong change of ice thickness and subglacial topography in small-scale means large bedrock roughness along the traverse,and is considered as the result of the integrated influence of ice flow,basal environments and geology.The segment where bedrock was not detected has very large ice thickness.The strong ice flow there also makes internal structure more complicated and induces serious attenuation of radar signals.
CUI XiangBinSUN BoTIAN GangTANG XueYuanZHANG XiangPeiJIANG YunYunGUO JingXueLI Xin
Dome A (Kunlun Station) is considered a likely place for finding an ice core record reaching back to one million years. The internal isochronous layering of the Antarctic Ice Sheet, revealed by ice radar, is a prerequisite for selecting sites for deep ice core drilling that can be used for studying the paleoclimatic record. In 2004/2005, during the 21st Chinese National Antarctic Research Expedition (CHINARE 21), a 200-km long, continuous radar profile was obtained across Dome A. The internal layers along the profile were derived from the stratigraphy detected by the radar. The morphology of the isochronous layers shows that: (1) The internal layers in the shallow ice sheet (0-500 m) are generally flat, with no more than 50 m of layer intervals, and have typical synclines and anticlines in some localized regions. (2) At 500-2000 m below the surface of the ice sheet, the layers appear as 'bright layers', and the width of the layer intervals expands to 50-100 m. (3) When the basal topographic wavelengths are approximate to the thickness of the ice (3 km), the traced internal layers, with localized bumps or concave folds, are asymptotic parallel to the subglacial topography. For the longer topographic wavelengths (~20 km) wider than the thickness of the ice, the layers do not rise and fall with the basal topography. The internal layers surrounding some mountain peaks representing the most extreme variation in the terrain are sharply disturbed by the subglacial topography. (4) Layer discontinuity and fracture were detected in the basal ice sheet. Finally, by combining this new information with that derived from existing data regarding ice thickness, we were able to select three potential sites for reconstructing the age-depth relationship of the ice core.
As an important component of the cryosphere, sea ice is very sensitive to climate change. The study of sea ice physics needs accurate sea ice thickness. This paper presents an electromagnetic induction （EM） technique which can be used to measure the sea ice thickness distribution efficiently and its successful application in the Antarctic Neila Fjord. Based on the electrical properties of sea ice and seawater and the application of electromagnetic field theory, this technique can accurately detect the distance between the EM instrument and the ice/water interface to measure the sea ice thickness. Analyzing the apparent conductivity data obtained by the electromagnetic induction technique and drill-hole measurements at same location allows the construction of a transform equation for the apparent conductivity and sea ice thickness. The verification of the calculated sea ice thickness using this equation indicates that the electromagnetic induction technique is able to determine reliable sea ice thickness with an average relative error of only 5.5%. The ice thickness profiles show the sea ice distribution in Neila Fjord is basically level with a thickness of 0.8 - 1.4 m.
Dome A, the highest dome of East Antarctic Ice Sheet, is being an area focused by international Antarctic community after Chinese Antarctic Expedition finally reached there in 2005, and with the ongoing International Polar Year （IPY） during August 2007. In this paper two data processing methods are used together to generate two 100-m cell size digital elevation models （DEMs） of the Dome A region （Dome A-DEM） by using Cokriging method to interpolate the ICESat GLAS data, with Ihde-DEM as a constraint. It provides fundamental data to glaciological and geophysical investigation in this area. The Dome A-DEM was applied to determining the ice-sheet surface elevations and coordinates of the south and north summits, defining boundaries of basins and ice ftowlines, deducing subglacial topography, and mapping surface slope and aspect in Dome A region. The DEM shows there are two （north and south） summits in Dome A region. The coordinate and the surface elevation of the highest point （the north summit） are 80°21＇29.86＂S, 77°21＇50.29＂E and 4092.71±1.43m, respectively. The ice thickness and sub-ice bedrock elevation at north summit are 2420m and 1672m, respectively. Dome A region contains four drainage basins that meet together near the south summit. Ice ftowlines, slope and aspect in detail are also derived using the DEM.
LIU JiyingWEN JiahongWANG YafengWANG WeiliBeata M CATHSOKenneth CJEZEK
