## 3 Validation of the Instrument v2021
### Autonomy and Satellite Communication Test in the Arctic: February 2021 Deployment
An ideal filter was applied to remove data below the lowest-frequency local minimum of  
Figure 5: Spectra obtained when testing the instrument v2021 in the laboratory. The signal-to-noise ratio is superior or equal to 50 for all test cases, except the “extreme” test case with displacements of amplitude 0.5 cm and period 16 s, where the signal-to-noise ratio is around 10. The noise threshold obtained when the instrument is at rest is actually slightly better than what was obtained with the instrument v2018 (compare the present plot with Figure 3 of [PERSON] et al. [51], curves “IMU 1” and “IMU 2”). the smoothed spectrum. In addition, another spectra comparison on 08:21 16 September is also provided on the right panel in Figure 7. By this time, the buoys were farther than 3 km apart, so there was a slight difference in energy levels between the two buoys but the general shape of the spectra is comparable. These buoy spectra comparisons indicate that the instrument v2021 can be used to measure ocean waves and is a full scale, fieldwork validation of the algorithms and processing used. Spotter buoys, without solar radiation recharge at high latitude during the winter season, have only a short life span, and SPOT-1386 ran out of battery on 30 September 2021. Analysis into the colocated deployment in and near the Marginal Ice Zone MIZ is ongoing and will be presented in a separate, science-focused paper. Notwithstanding, a comparison of wave periods (peak period \(T_{p}\) and spectral period \(T_{0m1}\)) when the buoys were less than 5 km-apart agree within better than 5%. In addition, the part of the dataset for which both instruments are frozen in the ice indicates that the noise level of the IMU-based instrument (typically around 0.1 cm) is much better than that of the Spotter buoy (typically around 1 cm), which is expected due to the different data sampling techniques used (GPS vs. 9-dof). This provides further support that Zeni-v2021 captured consistent energy densities to those of SPOT-1386 and that the Zeni-v2021 is actually better suited for measuring small waves in ice. Note that the analysis into the Zeni-v2021 and SPOT-1386 colocated deployment is described in a manuscript under preparation, which is why these data are not released in the present technical paper. Regarding battery life, the estimated deployment duration for hourly wave sampling rate was 3.3 months based on Table 1, where two Tadiran D-cell batteries (TL-5930/S), each with 19 Ah capacity, were used as the power source. The instrument stopped transmitting, likely due to an empty battery, in mid-December, i.e., 3 months after the start of the deployment. This corresponds well with the estimated battery life and is an additional confirmation of the quality of the hardware and software design, in particular, regarding the implementation of low-power modes. Figure 6: Zeni-v2021 and SPOT-1386 deployment location on 15 September 2021. The 2021 NAS-BOS observation locations also shown in green markers and AMSR2-derived 0.15 and 0.80 Sea Ice Concentration (SIC) contours for the same day are overlaid.