Sea ice is a major feature of the polar environments. Recent changes in the climate and extent of the sea ice, together with increased economic activity and research interest in these regions, are driving factors for new measurements of sea ice dynamics. Waves in ice are important as they participate in the coupling between the open ocean and the ice-covered regions. Measurements are challenging to perform due to remoteness and harsh environmental conditions. While progress has been made in observing wave propagation in sea ice using remote methods, these are still relatively new measurements and would benefit from more in situ data for validation. In this article, we present an open source instrument that was developed for performing such measurements. The versatile design includes an ultra-low power unit, a microcontroller-based logger, a small microcomputer for on-board data processing, and an Iridium modem for satellite communications. Virtually any sensor can be used with this design. In the present case, we use an Inertial Motion Unit to record wave motion. High quality results were obtained, which opens new possibilities for in situ measurements in the polar regions. Our instrument can be easily customized to fit many in situ measurement tasks, and we hope that our work will provide a framework for future developments of a variety of such open source instruments.Keywords Waves in ice ⋅ Open Source instrument ⋅ In situ measurements 1 Measurements of waves in iceThe interaction between surface waves and sea ice involves many complex physical phenomena such as viscous damping (Weber, 1987; Rabault and others, 2017), wave diffraction (Squire and others, 1995), and nonlinear effects in the ice (Liu and Mollo-Christensen, 1988). Therefore, it is complex and still an area of ongoing research (Rabault, 2018;Squire, 2018). Better understanding and modeling of wave propagation in sea ice can allow for the improvement of ocean models to be used for climate, weather and sea state predictions (Christensen and Broström, 2008), the estimation of ice thickness (Wadhams and Doble, 2009), and the analysis of pollution dispersion in the Arctic environment (Pfirman and others, 1995;Rigor and Colony, 1997). More generally, all these aspects must be better understood to allow safe, environment-friendly operations in the Arctic. Therefore, there is considerable interest in measuring sea ice dynamics.While the use of Synthetic Aperture Radar (SAR) images from satellites to obtain spectral wave information has made significant progress lately, they are still not standard measurements. Indeed, they require the satellite to be in a particular sampling mode (wide swath), as well as accurate prediction of the azimuth cutoff wavelength. This is vital for accurate determination of the wave energy, and is made complicated by the presence of sea ice (Ardhuin and others, 2017; Stopa and others, 2018). Therefore, in situ measurements are still a key method for measurements of waves in ice. In addition, as remote sensing and satellite-base...

ABSTRACT. Versatile instruments assembled from off-the-shelf sensors and open-source electronics are used to record wave propagation and damping measured by Inertial Motion Units (IMUs) in a grease ice slick near the shore in Adventfjorden, Svalbard. Viscous attenuation of waves due to the grease ice slick is clearly visible by comparing the IMU data recorded by the different instruments. The frequency dependent spatial damping of the waves is computed by comparing the power spectral density obtained from the different IMUs. We model wave attenuation using the one-layer model of Weber from 1987. The best-fit value for the effective viscosity is ν = (0.95 ± 0.05 × 10 −2 )m 2 s −1 , and the coefficient of determination is R 2 = 0.89. The mean absolute error and RMSE of the damping coefficient are 0.037 and 0.044m −1 , respectively. These results provide continued support for improving instrument design for recording wave propagation in ice-covered regions, which is necessary to this area of research as many authors have underlined the need for more field data.

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.

No abstract

[1] Heating during frictional sliding is a major component of the energy budget of earthquakes and represents a potential weakening mechanism. It is therefore important to investigate how heat dissipates during sliding on simulated faults. We present results from laboratory friction experiments where a halite (NaCl) slider held under constant load is dragged across a coarse substrate. Surface evolution and frictional resistance are recorded. Heat emission at the sliding surface is monitored using an infra-red camera. We demonstrate a link between plastic deformations of halite and enhanced heating characterized by transient localized heat spots. When sand 'gouge' is added to the interface, heating is more diffuse. Importantly, when strong asperities concentrate deformation, significantly more heat is produced locally. In natural faults such regions could be nucleation patches for melt production and hence potentially initiate weakening during earthquakes at much smaller sliding velocities or shear stress than previously thought.Citation: Mair, K., F. Renard, and O. Gundersen (2006), Thermal imaging on simulated faults during frictional sliding, Geophys.