Total ice and snow thickness was measured with portable electromagnetic instruments (EM31 and EM31SH, Geonics Ltd., Mississauga, Ontario, Canada) mounted on a sledge. The EM31s measure the received secondary electromagnetic field, induced by highly conductive seawater (Kovacs et al., 1991). Conductivity values are calibrated with drill hole measurements and post processed according to Haas et al., 1997.

[Figure 1]( https://api.npolar.no/dataset/70352512-fed8-4f1d-8b9c-30e6a764f5c2/_file/f5fa353f31a63b4d4167379acc785e73) shows the calibration curves for the two EM instruments used throughout the experiment.

In total 101 and 145 calibration drillings were made for EM31SH and EM31, respectively, covering a thickness range from 0.15 m to 4.50 m ice. Analysis of the calibration measurements did not reveal any drift in the fitting curve parameters on the temporal or spatial scales.

The footprint size of the EM31 ranges from 3 m to 5 m, depending on the ice and snow thickness. Accuracy of EM31 measurements is in the range of +-0.1 m for level ice, becoming higher for rough and deformed ice.

On all four Floes, independent (i) and repeated transects (t, tF, tM) with combined EM31 and snow depth measurements were performed.

Repeated transects are considered as repetitions of marked tracks on a weekly basis to observe temporal change, while independent transects are long surveys in different directions from the main ice camp are to cover the spatial variability of the surrounding area.