GEM-2 ice and platelet total thickness measurements for transect AFIN_ATKA_20221123@en

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.本数据集针对雪冰厚度（即从雪面至固结冰-片状冰界面的距离）与下伏片状冰厚度，采用电磁感应（Electromagnetic Induction, EM）方法开展测量。所有测线均采用由Geophex有限公司生产的GEM-2多频电磁感应仪传感器，将其挂载于雪地摩托后方的小型雪橇上进行拖行测量（Hunkeler等，2016b）。该仪器搭载实时数据处理单元，内置GPS接收机，可与掌上电脑通信，由后者操控传感器并记录电磁感应与GPS数据流。GEM-2为多频传感器，可同时发射多个可配置的kHz频段信号。在AFIN任务中，该传感器设置为5个频率，在其工作频段内呈近似对数间隔分布，分别为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：在每条测线的前后，均将GEM-2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。针对经校准的GEM-2勘测数据，通过修正版EMagPy框架（McLachlan等，2020）下的多频反演，实现雪冰、片状冰厚度与电导率的反演提取，该流程考虑了补偿线圈偏置（Hunkeler等，2016a）。为验证反演得到的厚度数据，我们采用与GEM-2测线同步获取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。如需更多细节，请参考Neudert等人2024年的研究论文：《利用多频电磁感应测深优化冰下片状冰层制图》（Improved sub-Ice Platelet Layer Mapping with multi-frequency EM Induction Sounding），该论文目前正在Elsevier旗下《应用地球物理学报》（Journal of Applied Geophysics）审稿中。