## 3 Validation of the Instrument v2021  
### Autonomy and Satellite Communication Test in the Arctic: February 2021 Deployment  
An early version of the instrument v2021, which performed drift tracking but no wave measurements, was deployed East of Svalbard in February 2021 [61]. This early version of the instrument was used to (i) validate the general design of the electronics; (ii) validate the low-power modes and the ability of the instrument to live for several months in the Arctic cold using just a couple of D-sized battery cells--in particular, regarding the power consumption of the iridium modem, which is hard to estimate; (iii) validate the satellite communication binary protocols. This initial test was a success. The instrument was deployed on 24 February 2021, East of Svalbard. It then transmitted data for a few weeks, before a snow storm covered it with snow and blocked the iridium transmission. This loss of communications is a consequence of the design of the housing of the instrument, which relied on a box that was too weak to survive even just 10 cm of snow and will be addressed in future designs by using a box that is higher and does not get buried as easily. However, communication with the Iridium satellites was restored when the ice melted in late May 2021. Following this, the instrument freely floated in the open sea, traveling all the way from Svalbard to the close vicinity of Murmansk, and back and forth between Novaya Zemlya and Murmansk. An overview of the trajectory is presented in Figure 3. At the time of writing this manuscript, i.e., January 2022, this instrument is still transmitting. The instrument was powered by 3 LSH20 batteries, which, since it measures only GNSS position each 30 min, should result in a battery life of around a bit over 1 year, following the data from Table 1. Therefore, this deployment validates the low-power design, and confirms that both the low-power sleep mode, the GNSS data acquisition, and the Iridium transmission (which have the power consumption that is most difficult to estimate) are correctly implemented and allow extended operation on battery alone. Figure 3: Overview of the drift trajectory of the early prototype instrument deployed in February 2021, East of Svalbard. The interruption in the trajectory is due to a layer of snow covering the instrument that prevented satellite communications during a couple of months. The instrument then drifted freely in the open ocean. This validates the low-power design and confirms that the chosen design is able to sustain operations for several months using just a few D-cell Lithium batteries. Experiments for Validation of Small-Amplitude, Low-Frequency Harmonic Vertical Displacement Measurements at the University of Tokyo's Wave-Ice Tank Facility: July 2021 Laboratory Test  
We conducted an experiment in July 2021 to evaluate the instrument v2021 accuracy for measuring small-amplitude harmonic vertical displacement representative of waves in ice. This experiment allows to fully validate (i) the acquisition of raw data from the 9-dof sensor, (ii) the processing algorithm and scaling factors used in the low-level signal processing code, and (iii) the data encoding used for transmitting the information back to the user. The experiment took place in the wave-ice tank facility at the Kashiwa campus of the University of Tokyo, Japan. In our case, however, the instrument v2021 prototype was placed on the top of the wavemaker paddle (which is a plunding wedge, vertical displacement paddle), rather than in the water (see Figure 4); so, it measured the vertical motion of the wavemaker itself, which is known to a very high accuracy thanks to the use of a closed-loop control. Indeed, even given the presence of a damping beach, it would be challenging in such a small wavetank to avoid reflections and standing waves, and to provide waves of sufficient amplitude at such low frequencies.