Arctic | Climate and Oceanography
Simultaneous measurement of sea ice thickness and water depth with multifrequency EM sounding Presenter: Achille Capelli , acapelli@alaska.edu, Geophysical Institute, University of Alaska Fairbanks Andrew Mahoney , armahoney@alaska.edu, University of Alaska Fairbanks Mapping sea ice thickness is relevant for a variety of human activities in polar regions including ice road transportation, marine navigation engineering and research. At the same time, the bathymetry of shallow water in these regions is often unknown and varies over time. Ground based and airborne EM sounding is a well-established technique for measuring sea ice thickness. Modern EM instruments are capable of measuring at multiple frequencies increasing the amount of information available for the inversion solution. We investigated the possibility of retrieving both sea ice total thickness and water depth from the inversion of multifrequency EM sounding. Both synthetic and field data were used to evaluate different inversion methods. For inversion and production of synthetic data we developed a 1-dimensional inversion scheme for a 3-layer conductivity model, including sea ice, sea water and the seafloor. The model is based on the open- source software package EMagPy. Field measurements were done near Utqiaġvik in April 2022 using a sled mounted EMP400 profiler that was towed over sea ice of varying thickness in water depths. The EMP400 operated at frequencies between 1kHz and 16 kHz and has a coils separation of 1.2m. Synthetic data shows that sea ice total thickness and water depth up to 6 m can be reliably measured with an instrument like the EMP400. However, for water depths shallower than 0.5 m the measurement accuracy decreases drastically. The inversion of the field data gave reliable results for both sea ice total thickness and water depth provided that a careful calibration of the measuring instrument is done. The developed method is applicable to both ground based and airborne EM data.
Alaska Marine Science Symposium 2023 124
Made with FlippingBook flipbook maker