GEM-2 quicklook total thickness measurements from the 2019-2020 MOSAiC expedition

• Main Authors: Hendricks, Stefan, Itkin, Polona, Ricker, Robert, Webster, Melinda, von Albedyll, Luisa, Rohde, Jan, Raphael, Ian, Jaggi, Matthias, Arndt, Stefanie
• Format: Dataset
• Language: English
• Published: PANGAEA 2022
• Subjects: Arctic; Arctic Ocean; Arctic Research Icebreaker Consortium: A strategy for meeting the needs for marine-based research in the Arctic; ARICE; BES; Broadband electromagnetic sensor; electromagnetic induction; GEM-2; ice; magnaprobe; MOSAiC; MOSAiC20192020; Multidisciplinary drifting Observatory for the Study of Arctic Climate; ocean; Polarstern; Priority Programme 1158 Antarctic Research with Comparable Investigations in Arctic Sea Ice Areas; PS122/1; PS122/1_10-51; PS122/1_10-55; PS122/1_4-2; PS122/1_4-3; PS122/1_5-25; PS122/1_5-26; PS122/1_6-48; PS122/1_6-49; PS122/1_7-60; PS122/1_7-61; PS122/1_8-55; PS122/1_8-56; PS122/1_8-57; PS122/1_9-51; PS122/1_9-52; PS122/2; PS122/2_16-48; PS122/2_16-50; PS122/2_16-77; PS122/2_16-82; PS122/2_17-111; PS122/2_17-112; PS122/2_18-78; PS122/2_18-79; PS122/2_19-102; PS122/2_19-104; PS122/2_19-105; PS122/2_19-108; PS122/2_19-109; PS122/2_19-111; PS122/2_19-112; PS122/2_19-136; PS122/2_19-138; Antarctic; Antarc*; Sea ice
• Online Access: https://doi.pangaea.de/10.1594/PANGAEA.943666; https://doi.org/10.1594/PANGAEA.943666

The total snow and ice thickness (distance from the snow surface to the ice-ocean interface) was measured by the electromagnetic induction (EM) method. On MOSAiC transects, we used a broad-band EM instrument sensor (GEM-2 by Geophex Ltd) towed on a small sled (Hunkeler et al, 2015; Hunkeler et al, 2016). 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 broadband sensor that can transmit multiple configurable frequencies in the kHz range simultaneously. The sensor setup during MOSAiC used 5 frequencies with an approximately logarithmic spacing throughout the frequency range of the sensor (1.525 kHz, 5.325 kHz, 18.325 kHz, 63.025 kHz, and 93.075 kHz). The transect measurements are based on an empirical approach based on a sensor calibration, where the GEM-2 was placed at known heights above the sea ice surface using a wooden ladder on top of level ice with a known thickness determined by 5 drill holes. An exponential function was then fitted to the frequency components as function of distance of the sensor to the ice/ocean interface and then applied to the transect data. The closest-in-time calibration result was used when a GEM-2 survey could not be accompanied with a calibration. The total thickness retrieval with the GEM-2 calibration and survey data was done on-board shortly after each profile. The dataset is therefore labeled as GEM-2 quickview data but has been subject to manual quality control. Using a direct relationship between total thickness and frequency component implies the assumption that the sea ice conductivity is negligible and the ice/water interface constant within the GEM-2 footprint. While this is a reasonable assumption for level ice, the peak thicknesses of ridges are known to be underestimated by as much as 50 % (Pfaffing et al, 2007) and will be subject of further processing. To estimate the snow depth and then subtract its thickness from ...