2012 refrozen melt layer location, density, and connectivity records from airborne radar sounding, Greenland, 2017

Surface meltwater runoff dominates present-day mass loss from the Greenland Ice Sheet. In the interior, porous firn can buffer runoff by retaining meltwater unless perched impermeable horizons, such as ice slabs, develop and restrict percolation. Recent field observations suggest that such horizons might develop rapidly during extreme melt seasons. In particular, subsurface refreezing of surface meltwater during the 2012 extreme melt season created a spatially coherent refrozen melt layer across the Greenland Ice Sheet. We use airborne radar sounding data collected by the University of Kansas Center for the Remote Sensing of Ice Sheets (CReSIS) to map the extent of this layer and constrain its density and lateral connectivity at the radar footprint scale. These observations provide insights into the multi-year impact of extreme melt seasons on firn structure and meltwater drainage pathways. This data set contains detections of this melt layer from Accumulation Radar data collected by CReSIS in 2017. We use an electromagnetic forward model to invert the observed radar reflectivity to constrain the layer density and measure connectivity based on the number of laterally adjacent detections. File 2012IceLayerDetections.txt contains the latitude, longitude, layer prominence, the probability that layer density exceeds pore close-off, lateral layer connectivity, the minimum layer density consistent with the observed radar reflectivities, and the maximum layer density consistent with the observed radar reflectivities, all averaged to 1kilometer (km) grid cell along the flight lines. The files [Date]_[Segment]_CleanResults.txt contains the same data, but broken out into 18 individual text files, one for each radar flight transect analyzed. The date and segment match the CReSIS flight date and segment assigned to the analyzed radargrams.表层融水径流是当前格陵兰冰盖质量损失的主导因素。冰盖内部的多孔粒雪（firn）可通过留存融水缓冲径流，但若形成冰盖这类悬托不透水层，则会限制融水下渗。近期野外观测表明，这类不透水层可能在极端融冰季快速形成。具体而言，2012年极端融冰季中，表层融水在地下发生再冻结，在整个格陵兰冰盖范围内形成了空间分布连贯的再冻结融冰层。本研究使用堪萨斯大学冰盖遥感中心（Center for the Remote Sensing of Ice Sheets, CReSIS）采集的机载雷达测深数据，绘制了该融冰层的分布范围，并在雷达足印尺度上限定了其密度与横向连通性。这些观测结果有助于揭示极端融冰季对粒雪结构与融水排泄路径的多年级影响。 本数据集包含CReSIS于2017年采集的累积雷达（Accumulation Radar）数据中该融冰层的识别结果。本研究采用电磁正演模型，对观测到的雷达反射率进行反演，以限定该融冰层的密度，并基于横向相邻识别点的数量量化其连通性。文件2012IceLayerDetections.txt包含以下数据：纬度、经度、融冰层突出度、融冰层密度超过孔隙封闭阈值的概率、融冰层横向连通性、与观测雷达反射率相符的最小层密度，以及与观测雷达反射率相符的最大层密度，所有数据均沿飞行航线按1千米（km）网格单元进行平均。 名为[Date]_[Segment]_CleanResults.txt的文件包含相同的数据，但拆分为18个独立的文本文件，每个文件对应一条经分析的雷达飞行测线。其中的日期与分段编号与CReSIS为所分析雷达测深图分配的飞行日期及分段编号一致。