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).