There is a wide consensus within the polar science, meteorology, and oceanography communities that more in situ observations of the ocean, atmosphere, and sea ice are required to further improve operational forecasting model skills. Traditionally, the volume of such measurements has been limited by the high cost of commercially available instruments. An increasingly attractive solution to this cost issue is to use instruments produced in-house from open-source hardware, firmware, and postprocessing building blocks. In the present work, we release the next iteration of the open-source drifter and wave-monitoring instrument of Rabault et al. (see “An open source, versatile, affordable waves in ice instrument for scientific measurements in the Polar Regions”, Cold Regions Science and Technology, 2020), which follows these solution aspects. The new design is significantly less expensive (typically by a factor of 5 compared with our previous, already cost-effective instrument), much easier to build and assemble for people without specific microelectronics and programming competence, more easily extendable and customizable, and two orders of magnitude more power-efficient (to the point where solar panels are no longer needed even for long-term deployments). Improving performance and reducing noise levels and costs compared with our previous generation of instruments is possible in large part thanks to progress from the electronics component industry. As a result, we believe that this will allow scientists in geosciences to increase by an order of magnitude the amount of in situ data they can collect under a constant instrumentation budget. In the following, we offer (1) a detailed overview of our hardware and software solution, (2) in situ validation and benchmarking of our instrument, (3) a fully open-source release of both hardware and software blueprints. We hope that this work, and the associated open-source release, will be a milestone that will allow our scientific fields to transition towards open-source, community-driven instrumentation. We believe that this could have a considerable impact on many fields by making in situ instrumentation at least an order of magnitude less expensive and more customizable than it has been for the last 50 years, marking the start of a new paradigm in oceanography and polar science, where instrumentation is an inexpensive commodity and in situ data are easier and less expensive to collect.

Acoustic experiments using an integrated ice station were carried out during August 2012 and September 2013 in the Marginal Ice Zone (MIZ) of Fram Strait. The two experiments lasted four days each and collected under-ice acoustic recordings together with wave-in-ice and meteorological data. Synthetic aperture radar satellite data provided information on regional ice conditions. Four major components of the under-ice soundscape were identified: ship cavitation noise, seismic airgun noise, marine mammal vocalizations, and natural background noise. Ship cavitation noise was connected to heavy icebreaking. It dominated the soundscape at times, with noise levels (NLs) 100 km from the icebreaker increased by 10-28 dB. Seismic airgun noise that originated from seismic surveys more than 800 km away was present during 117 out of 188 observation hours. It increased NLs at 20-120 Hz by 2-6 dB. Marine mammal vocalizations were a minor influence on measured NLs, but their prevalence shows the biological importance of the MIZ. The 10th percentile of the noise distributions was used to identify the ambient background noise. Background NLs above 100 Hz differed by 12 dB between the two experiments, presumably due to variations in natural noise sources.

A characteristic surface duct beneath the sea-ice in the Marginal Ice Zone causes acoustic waves to be trapped and continuously interact with the sea-ice. The reflectivity of the sea-ice depends on the thickness, the elastic properties, and its roughness. This work focuses on the influence of sea-ice roughness on long-range acoustic propagation, and on how well the arrival structure can be predicted by the full wave integration model OASES. In 2013, acoustic signals centered at 900 Hz were transmitted every hour for three days between ice-tethered buoys in a drifting network in the Fram Strait. The experiment was set up to study the signal stability in the surface channel below the sea-ice. Oceanographic profiles were collected during the experiment, while a statistical description of the rough sea-ice was established based on historical ice-draft measurements. This environmental description is used as input to the range independent version of OASES. The model simulations correspond fairly well with the observations, despite that a flat bathymetry is used and the sea-ice roughness cannot be fully approximated by the statistical representation used in OASES. Long-range transmissions around 900 Hz are found to be more sensitive to the sea-ice roughness than the elastic parameters.

Seismic mapping of the shallow, coastal areas of the Arctic is best facilitated in periods when the sea is covered with solid, floating ice. Data from three seismic acquisition campaigns on sea ice floating on shallow water reveal how coherent noise related to guided waves is differently exposed for various source and receiver systems placed on and below the ice. The main coherent noise is due to interference of ice flexural and Scholte waves. The experimental data were overall successfully modeled using a wavenumber integration technique. A seismic source at or near the ice generates high-amplitude, slowly propagating, and highly dispersive flexural waves. Their amplitudes are severely reduced when recorded at hydrophones deployed 5 m or more below the sea ice. The extent of flexural waves generated using an air gun below the ice similarly reduces as the depth of the air gun increases, but then the amplitudes of the seabed Scholte waves increase. Our experiments indicate that an inline line source of detonating cord on the ice combined with hydrophones deployed at the appropriate depth below the ice constitute an efficient setup for reducing the imprints of the ice flexural and Scholte waves on seismic data.

The under-ice acoustic transmission experiment of 2013, conducted under ice cover in the Fram Strait, was analyzed for bottom interactions for the purpose of developing a model of the seabed. Using the acoustic signals, as well as data from other sources, including cores, gravimetric, refraction, and seismic surveys, it was deduced that the seabed may be modeled as a thin surficial layer overlaid on a deeper sediment. The modeling was based on the Biot–Stoll model for acoustic propagation in porous sediments, aided by more recent developments that improve parameter estimation and depth dependence due to consolidation. At every stage, elastic and fluid approximations were explored to simplify the model and improve computational efficiency. It was found the surficial layer could be approximated as a fluid, but the deeper sediment required an elastic model. The full Biot–Stoll model, while instrumental in guiding the model construction, was not needed for the final computation. The model could be made to agree with the measurements by adjusting the surficial layer thickness.