Collaborative Research: Subglacial Water Intrusion in Greenland

A full understanding of the flow and dynamics of an ice sheet will require knowledge of the state of its subglacial interface. While the topography of the Greenland Ice Sheet (GrIS) bed has been studied by radio echo sounding, its state in terms of melting and freezing, which itself affects its future evolution, has been inferred from numerical models, rather than from direct evidence. This project is for analysis of existing radar echo data gathered under the Program for Arctic Regional Climate Assessment (PARCA) and Center for Remote Sensing of Ice (CReSIS) programs, with the objective of generating direct evidence of the extent of subglacial water in Greenland and providing the glaciological community with maps of its extent. Previous echo analysis has found the variability of the received signal too great to extract the component due to variation of the bed material. Now, a method has been developed, validated and reported, based on further analysis of radio echo signal intensities, which allows the state of the bed to be determined reliably. This work will apply this method to all the available radio echo data, to generate maps of the extent of basal melting throughout Greenland. The procedure relies on a more precise assessment of radio echoes from the bed of the ice sheet than has previously been provided. It allows the variability of echo intensity to be reduced, and the variation of the bed material to be detected. It has been tested with data from a number of flights over Greenland during the 1999 field season, and is validated by tests of self-consistency, of echo intensity statistics, of interface smoothness, and of the relation between measured surface and interface slopes. The team will process data from flights undertaken between 1998 and 2005. Appropriate tests of self-consistency and statistical behavior will be applied. The presence or absence of water will be determined throughout. Results will be interpreted and maps compiled illustrating these results. The continuity and topographical context of each major water feature will be investigated and compared.

要全面理解冰盖的流动与动力学特征，需掌握其冰下界面的状态。此前，学界已通过无线电回声测深（radio echo sounding）对格陵兰冰盖（Greenland Ice Sheet, GrIS）的床层地形开展研究，但关于其融冻状态——这一状态本身会影响冰盖未来演化——的认知，多源自数值模型推演，而非直接观测证据。本项目将对北极区域气候评估计划（Program for Arctic Regional Climate Assessment, PARCA）与冰盖遥感中心（Center for Remote Sensing of Ice, CReSIS）采集的现有雷达回声数据开展分析，目标是获取格陵兰岛冰下水分布范围的直接观测证据，并为冰川学界提供冰下水分布地图。过往的回声分析曾面临接收信号变异性过大的问题，无法提取由床层物质变化带来的信号分量。如今，研究团队基于对无线电回声信号强度的进一步分析，开发、验证并报道了一种可可靠确定冰盖床层状态的方法。本研究将把该方法应用于所有可用的雷达回声数据，以生成覆盖全格陵兰岛的基底融化范围分布图。该流程相较于此前的研究，可实现对冰盖床层无线电回声的更精准评估：不仅能降低回声强度的变异性，还可检测床层物质的变化。该方法已通过1999年野外作业期间格陵兰岛多架次飞行采集的数据进行了测试，并通过自洽性检验、回声强度统计特性检验、界面光滑性检验以及实测地表坡度与界面坡度间的关联性检验完成了验证。研究团队将处理1998年至2005年间的所有飞行采集数据，并开展相应的自洽性与统计特性检验，以全面判定各处是否存在冰下水。随后将对结果进行解读，并编制相关地图以直观展示这些成果。此外，还将对各主要水体特征的连续性与地形背景展开调查与对比分析。