【作者】 张向培；

【导师】 田钢；

【作者基本信息】 吉林大学 ， 地球探测与信息技术， 2007， 硕士

【摘要】 本文主要介绍冰雷达探测技术的原理、资料处理和解释方法以及在东南极冰盖中的应用。为了了解东南极中山站——Dome A区域冰下地形状况和冰盖内部特征,我们利用冰雷达探测技术(RES)对中山站——Dome A顶点整个断面进行连续测量,获得了17200道冰雷达数据,共1312km长。冰雷达系统是由两个单频脉冲雷达安装在冰雪交通工具上实现的,两个电磁波频率分别为60MHz和179MHz。我们利用冰雷达数据得到了内部反射层的“等时性”,并了解了等时冰层的形成机制,同时利用这两种频率分辨出由于电导率变化引起的反射和介电常数变化引起的反射的差异。从整个断面冰体厚度结果和Dome A顶点三维厚度分析可以看出整个断面上最厚的冰厚3129米,最高点高程4090米,在最高点处沉积环境比较稳定,是最有可能得到年代最久远的深冰芯钻取的位置。文中还简单讨论了一下冰下地形环境。更多还原

【Abstract】 The paper, supported by national natural science foundation program“The structure and ages of internal layers and the rebuilding of the accumulation of speed in past 100,000 in Dome A of East Antarctic Ice Sheet”and the ministry of science and technology social commonweal research program“The research of ocean-ice-atmosphere survey along Prydz Bay to Dome A in Antarctic”, aiming primarily at the whole radar p2rofile of Zhongshan-Dome A, analysed the ice thickness and the characteristic of subglacial terrain and the 3-D ice penetrating radar data of the region in central Dome A .An essential property of Antarctic ice sheet is that full deposited sequences of ice layers were preserved. This made the ice sheet become a carrier of age-old environmental information apposed with deep-sea and loess deposit. Additionally, changes of ice sheet （mass and dynamic balance） still affected directly the global sea level and temperature salt circumfluence. It is significant to detect the ice thickness, internal ice layers and subglacial terrain of Antarctic ice sheet. The distribution and architecture of ice sheet isochronous layers recorded the deposited process and information of ice sheet flow and evolvement. The data of shallow ice isochronous layers can be used to estimate the average and recent accumulation rate. The data of deep internal ice layers supplied the historical records of snow prophase accumulation rate and water flow velocity. Through the incorporation of these data, we can understand how ice sheets respond to climate better. Ice thickness and the feature of bed topography, such as roughness and slop, as parameter can be used to model. In addition, the radio echo signals reveal the subgalcial environment, the dynamic process and thermal process. Today, RES from ground-based and airborne platforms remains the most effective tool for measuring ice thickness and internal character.Radio-echo sounding （RES）, or radar, is based on the transmission and detection of electromagnetic waves at frequencies of between 1 and 1000MHz to investigate the internal and basal properties of ice masses. Radar waves, when they propagate through the ice masses, whose path、strength and transform are influenced by electric and geometric of the dielectric. Therefore, we can investigate a variety of ice-mass properties according the relationship between two-way travel time of recorded signal and depth in the host medium.Radar signal propagation in ice is essentially controlled by two electrical properties: （1） relative electrical permittivity; and （2） electrical conductivity. Electrical permittivity (Fm^-1) describes the capacity of ice to store an electrical charge, effectively impeding the flow of an applied electrical current. Permittivity is normally described relative to that in free space (8.854×10-12Fm^-1), termed relative permittivityε_r. There are two known cause which cause changes in dielectric permittivity: 1) density fluctuations （P_D）. Near the surfaces of the ice masses upper 800m, extensive melting, depth hoar, or precipitation hiatuses can cause changes in density large enough to create strong reflections. 2) crystal-orientation fabrics (P_COF). In the deeper layers, because of the densification of ice and phase of air bubbles into clathrate hydrate crystals the crystal-orientation fabrics are changes to create strong reflections.Electrical conductivity (mS m^-1) （CA） describes the ability of a material to conduct an applied electrical current. The electrical conductivity is principally controlled by the ice’s ionic, or impurity, content. Such impurities are primarily derived from sea-salt or volcanic aerosol deposits. In many papers the cause of internal reflections from deeper layers has been assigned simply to changes in electrical conductivity due to changes in acidity.Therefore, according to the dielectric of isochronous layers, we used a multi-frequency ice- penetrating radar system to measure the internal reflections layers and research the dynamics in the ice.In this paper, I present the physical theory and principles of radio-glaciology, and describe the radar system, including the techniques and parameter of radar. To better understand the ice thickness and bed topography in Dome A, we use a ground-based, multi-frequency ice-penetrating radar system, collected the radar data along the Zhongshan Station to the Summit of Dome A during the 2004-2005.The spatial change of internal reflections and distortion of isochronous layers in ice revealed by ice-penetrating radar. These reflections are generally accepted to result from layers of isochronous deposition of snow and can reveal much about the dynamics of the ice flow. The ice thickness and bedrock roughness as parameters applied in model of ice sheet. Though analysis of the radar data, we get the ice thickness to find the optimal site for drilling the deep ice core. Form the differences of the multi-frequency （60MHz and 179MHz） radio echo response at various sites, we clarify the dominant cause of internal reflections.From the radar profile along the Zhongshan station to Dome A, the data show arches and troughs in isochronous ice layers. In some sites the inclined layers and distortion of isochronous layers in ice revealed by ice-penetrating radar. We also find there is no radar signal in some sites and some sections exhibit instable sedimentation and discontinuation of the internal reflections. At Dome A, the changes of surface elevation is not obvious, the highest is 4090m. The data of ice-penetrating radar revealed flat isochronous layers. In addition, bed topography appears to be the result of a saddle-backed basin. From these feature, there is to be thought the best site to drill the deep ice core around the Dome A.Through the multi-frequency radar experiments, three reflection mechanisms, P_D、P_COF and C_A , were identified in the ice sheet in different depth ranges. From the observations, we found that the upper 700-900m of the ice sheet is dominated by the changes in permittivity due to changes in density. Below the upper 700-900m, some zones in the ice sheet are dominated by the changes in permittivity due to changes in crystal-orientation fabrics and some are by the changes in conductivity due to changes in acidity. Ice radar is not only a tool to detect boundary conditions of ice sheets （surface, bed, and isochrones） but is also a tool which reveals internal physical process.更多还原