This dataset contains the raw electromagnetic induction (EM) measurements from repeated walks with the GEM instruments on a sledge across ice floes (called long transects) conducted during the PS149 CONTRASTS expedition. All measurements were acquired using the Geophex Ltd. GEM-2-730 broadband EM sensor. During each ice station (i.e., floe visit), a long transect was traversed across the ice floe to obtain statistically representative distributions of snow/pond depth and ice thickness. Each transect was marked with flags at its corner points to ensure that a similar track was measured during repeated visits to each ice floe. This dataset provides only the raw GEM measurements acquired along these transects, including in-phase and quadrature responses, as well as electrical conductivity and magnetic susceptibility of sea ice and snow / melt ponds. These raw data enable users to apply various processing methods to, e.g., derive sea ice thickness. For reference, processed sea ice thickness derived from these measurements (using the gem2-seaice-toolbox, https://gitlab.awi.de/sitem/gem2-seaice-toolbox), along with co-located MagnaProbe snow and pond depth measurements, are available in the Level 2 dataset (doi:10.1594/PANGAEA.996908).
This data collection, assembled as part of the Arctic PASSION project, encompasses 96 Snow and Ice Mass Balance Array (SIMBA) buoys that were deployed between 2012 and 2023 in the Arctic Ocean (predominantly the Transpolar Drift Stream) and the Southern Ocean (Weddell Sea/Atka Bay). SIMBAs are thermistor string type IMBs (Jackson et al., 2013) which measure the environmental temperature SIMBA-ET and a temperature change around the thermistors after a weak heating is applied to each sensor (SIMBA-HT). Based on a manual classification method, the SIMBA-ET and SIMBA-HT were processed to obtain snow depth and ice thickness (smoothed with a 3-day running mean), as well as the thermistor number, the vertical position Z relative to the snow-ice interface and the measured SIMBA-ET at each detected interface (atmosphere-snow, snow-ice and ice-ocean). To do this, we combined two derivatives of measured temperatures (the ET vertical gradient and HT rise ratio) to reduce the detection uncertainty of all interfaces considered. The snow and/or ice surface, consequentially the snow depth, is determined by the ET vertical gradient. Potential formation of snow ice is not explicitly considered in this data set, but may occur as depicted by vertical changes of the snow-ice interface position. The ice-ocean interface is usually determined using the HT rise ratio and serves as the lower limit for ice thickness. Overall, the accumulated error is 2 to 4 times the sensor spacing for both the snow depth and ice thickness. For interface temperatures, individual sensors in the chain measure with a temperature resolution of 0.0625°C, with the overall accuracy landing in the range of ± 2°C (Jackson et al., 2013). After the snow cover has melted, negative values for snow depth may indicate the onset of ice surface melt.
Raw EM data obtained during the 2020 IceBird MOSAiC Summer campaign using the research aircraft POLAR 6. Data was gathered during two test flights over open water (August 05 and 31) and three flights from Longyearbyen, Svalbard over sea ice in the western and northern Fram Strait on September 02, 07, and 08, 2020.