GEM-2 ice and platelet total thickness measurements for transect AFIN_ATKA_20221212

The snow+ice thickness (distance from the snow surface to the consolidated ice-platelet ice interface) and the underlying platelet ice thickness was measured by the electromagnetic induction (EM) method. On all transects, we used a multi-frequency EM instrument sensor (GEM-2 by Geophex Ltd) towed on a small sled behind a snowmobile (Hunkeler et al, 2016b). The instrument includes a real-time data processing unit including a GPS receiver which communicates with a pocket PC that is operates the sensor and records the EM and GPS data streams. The GEM-2 is a multi-frequency sensor that can transmit multiple configurable frequencies in the kHz range simultaneously. The sensor setup during AFIN used 5 frequencies with an approximately logarithmic spacing throughout the frequency range of the sensor (1.53, 5.31, 18.33, 63.03, and 93.09 kHz). The transect measurements are based on a sensor calibration, where the GEM-2 was placed in a zero-conductivity environment on the ice shelf before and after each transect to correct for signal offsets in instrument drift. The snow+ice and platelet ice thickness and conductivity retrieval of the calibrated GEM-2 surveys data was done by multi-frequncy inversion in the modified framework of the EMagPy (McLachlan et al., 2020) accounting for the bucking coil bias (Hunkeler at al., 2016a). To validate the retrieved thicknesses, we used the snow depth, ice thickness and platelet ice thickness from the drill hole measurements coincident with the GEM-2 transects. The coincident drill hole data can be found here: doi:10.1594/PANGAEA.968459. For more details we refer to the paper by Neudert et al, 2024: Improved sub-Ice Platelet Layer Mapping with multi-frequency EM Induction Sounding, in review at Journal of Applied Geophysics, Elsevier.本数据集所涉及的雪冰总厚度（雪面至固结冰-片状冰界面的垂直距离）与下伏片状冰厚度，均通过电磁感应（Electromagnetic Induction，简称EM）方法测得。所有测线均采用由Geophex有限公司生产的GEM-2型多频电磁感应传感器，将其挂载于雪地摩托后方的小型雪橇上开展测量（Hunkeler等，2016b）。该仪器搭载实时数据处理单元，内置GPS接收机，可与操控传感器并记录电磁感应与GPS数据流的掌上电脑进行通信。GEM-2型传感器为多频设备，可同时发射kHz频段内多组可配置频率的信号。本次AFIN项目中的传感器配置采用5个频率，在传感器全频段范围内以近似对数间隔排布（1.53、5.31、18.33、63.03与93.09 kHz）。测线测量基于传感器校准流程：在每条测线开展前后，均将GEM-2型传感器置于冰架上的零电导环境中，以校正仪器漂移带来的信号偏移。经校准的GEM-2型传感器测量数据中，雪冰总厚度、片状冰厚度与电导率的反演提取，依托改进版EMagPy框架（McLachlan等，2020）中的多频反演方法完成，并考虑了补偿线圈偏置的影响（Hunkeler等，2016a）。为验证反演得到的厚度数据，研究人员采用了与GEM-2测线同步开展的钻孔测量所得雪深、冰厚与片状冰厚度数据。该同步钻孔数据集可通过以下DOI获取：10.1594/PANGAEA.968459。更多细节可参阅Neudert等（2024）的论文《Improved sub-Ice Platelet Layer Mapping with multi-frequency EM Induction Sounding》，该文目前正在Elsevier旗下《应用地球物理学报》（Journal of Applied Geophysics）审稿中。