The Study On The Inner Structure And Tomography Of East Antarctic Based On Two-Frequency And Multi-Polarization Plane Method Of Radio-Echo-Sounding (RES)

The Study on the Inner Structure and Tomography of East Antarctic Based on Two-Frequency and Multi-Polarization Plane Method of Radio-Echo-Sounding (RES)Ph.D Supervisor: Prof. Gang Tian and Prof. Bo Sun Major: Geo-exploration and Information TechnologyAntarctic ice sheets play a crucial role in global climatic system, the state and tendency of mass balance influence the changes of global sea level and thermo-salt circumfluence significantly. Therefore, it is indispensable to understand ice stream mechanisms and dynamic processes for interpreting the past, present, and future changing law of ice sheet. The two-frequency polarization radar provides an indirect technical method to demonstrate the character of ice medium.Radio-Echo Sounding (RES) was used to detect the thickness of glaciers and ice sheets since 1960s, and had achieved great success as an important technique in ice-sheet exploration due to its convenience, high efficiency and accuracy. In 1990s, the four-year plan of BEDMAP implemented by BAS put forward special data-base of ice thickness and sub-glacial terrain covered Antarctic continent, and thereinto, 90% data came from radar sounding. RES not only can be used in ice-sheet thickness and sub-glacial terrain exploration, but also used in researching of space change and physical process of crystal-orientation fabrics. In 1999, summarizing former's achievements, based on the study of mass character of ice cores, Fujita suggested to use the two-frequency RES to distinguish reflecting layers caused by dielectric permitivity or conductivity. In 2003, Matsuka used dual-frequency and multi-polarization plane radar to research the space change of crystal-orientation fabrics in Shirase glaciers.During the 21st South Pole ice-sheet investigation, the advanced two-frequency RES system was employed to survey the area between ZhongShan and Dome A, and got a set of valuable radar data. This paper, reviewed the past, present and future of the development of RES firstly, and then aimed at the technical characteristic and research progress of two-frequency RES, made further research and detailed discussion finally. We discussed on three topics primarily: forward simulation of electromagnetic wave response of anisotropic, processing software development and data process and interpretation of ZhongShan-Dome A radar data.1. At present the commonly viewpoint is: internal reflections in ice sheet caused mostly by dielectric permittivity changes due to density fluctuations and(or) crystal-orientation fabrics changes and electrical conductivity changes due to changes in acidity(related to volcanic eruptions). Thro ugh experiments, some scholars found that heavy-acidity or anisotropic ice can cause detectable radar reflection. The paper, started off the equation of Maxwell, deduced the FDTD formula fit to the anisotropic and worked out the corresponding program. We made a set of arranged models which parameters were derived from the others experiment result, to simulate the various phenomenons of radar reflection in real Antarctic sheet. It includes:A. The simulating result shows that the distinct reflection appeared if only changing the layer conductivity and keeping the permittivity in the model. B. The responding output of anisotropic medium was simulated in the case of antenna rotation. The simulating result shows that the strength of output voltage variated with rotation angle and had 180°period. C. The simulation results of the output differences of the three types of antenna commonly used in ice radar show that the type C is more sensitive to the difference between anisotropic and isotropic. D. The output differences in different antennas type were compared when the permittivity of the anisotropic medium changed. The result show that, to the type B, the arriving time from bed in the type A has "bring-forward" or "delay" phenomenon, and it depend on the wave impedance difference between the upper and the below layer. Based on these experiments, we presented a simple method for distinguishing the direction of ice flow by comparing the arriving time difference of the ice bed reflection in the two antenna type.2.There are great differences between dual-frequency-polarization RES andtraditional RES in the collection method and proceeding and interpretationmethod, since dual-frequency-polarization RES is a new ice radar technique. Wecan obtain four sets of radar data in case of a single profile at least. These mayinclude data from two kinds of frequency (for example, 60 and 179MHz) and twopolarization directions. The data contain abundant information of the inner layers.We can extract them by subtracting between the different data, therefore we caninterpret the forming cause of the inner reflection layer (from the change ofdensity or acid or COF). We gave entire summarization on the proceeding methodof the dual-frequency-polarization RES.The present actuality of the RES data proceeding technique exist in two points. The first is that the quantity of the RES data is huge. The proceeding works need a lot of time and the period of the data transformation is relatively long. The second is that the resource and superiority of the collective division and cooperation isn't used fully. Summarizing the technique of the dual-frequency-polarization RES, I developed a software applied in RES data proceeding of the China 21th Antarctic Expedition, and improved the efficiency greatly.3.Based on the RES result of the China 21th Antarctic Expedition proceedingby my software, we interpreted some data obtained during the expedition. Firstly,we found a north-east deep channel according to 3D RES exploration result inDome A, its ice thickness exceeded 3000m. This provided the target area forsearch the oldest ice and the china deep ice core project. Secondly, We analyzedand interpreted the multi-polarization plane result, and compared it with the deepcore record in Dome Fuji. According to the comparing result, we proposed thatthe inner ice at the survey point in Dome A may be composed of elongated single-pole COF. In addition, based on the RES time-depth-conversion result, we obtained the ice-bed elevation and tomography combined with the surface elevation data. The RES result has higher precision than the data from BEDMAP database.Based on the dual-frequency comparison, we analyzed the inner composition of the ice sheet in the Dome A- ZhongShan station section with large scale. Then a certain section with dual-frequencies and dual-polarizations was selected. We compared the results with diferent frequencies and polarizations and analyzed some corresponding points. According to the conclusion derived from simulation in chapter 4, the arriving time from the bottom of anisotropy layer has difference in the different antenna type. We chose some corresponding points with different polarization to estimate the ice flow direction. The statistic result showed that most of the deduced results were consistent with the real case.