## 5 Arctic-Based Field Observations
One of the notable remarks of the observation was that localized sea ice dynamics will need to be considered for future melt onset algorithm development from multi-sensor \(\gamma_{\text{C}}\)\({}^{\circ}\) SAR products. The ability of the multi-sensor products to identify the ice melting phenomenon shows that these products could be utilized for lead detection studies. At the end of the 2010s, research addressed the development and validation of low-cost sensors for Arctic-based research. [PERSON] et al. [103] provided a study to ensure the operational performance of a low-cost tool for atmospheric and meteorological observations. For verification of the proposed tool, Vaisala HMP45 AC and Campbell-Scientific EC150 were taken as reference sensors. On the other hand, [PERSON] et al. [104] constructed an instrument to enhance progressive research on measuring snowpack and ice thickness. The tool adopts the concept of the frequency-modulated continuous-wave (FMCW) radar. Even though this instrument can be attached to an autonomous vehicle, an unfavorable environment outside the radar's limits may hinder the measurement process and lead to unrealistic results, e.g., during ice and wet snow situations. Landmarks studies of sensor application in Arctic research from the early 2010s until 2020 are summarized in Table 5.  
\begin{table}
\begin{tabular}{c c c c} \hline
**Milestone** & **Author(s)** & **Observational Subject** & **Tools/Instrument** & **Important Remarks** \\ \hline \multirow{4}{*}{2010} & \multirow{4}{*}{[PERSON] and \(\begin{array}{c}\text{[PERSON]}\\ \Based on the review, it can be concluded that atmospheric and hydrological systems are the primary research subjects using sensor tools/instruments in the Arctic region. At the end of the decade, a sensor was used collaboratively with an autonomous vessel. As promising results were obtained, research may be continued to provide observational and measurement sensors on vessels in the current decade. This prediction is quite realistic,as [PERSON] et al. [105] addressed their concern regarding wave measurement of the Arctic marginal ice zone (MIZ) by using a mounted sensor on ship waves. An ultrasonic gauge (UG) was taken as the setup instrument to measure ocean surface elevation. Inertial motion units (IMUs) were deployed to measure data reliability and changes in dynamic sea motion. Notable results were processed with wave spectral models, i.e., wave attenuation measurement (WAM) and ERA5 (see Figure 17). A comparative study was also conducted to analyze wave measurement from several instruments, namely, WAM and wave-in-ice instruments (WIIs), as presented in Figure 18. The results indicate that the greatest disparity (represented by the mean percentage error) in the wave height and zero-up crossing period from the WAM and WII was below 9.7%, observed at stop 1.3 with a difference of 87.8%. Figure 17: Comparison of the measurement data from WAM-4 (**a**,**b**) and ERA5 (**c**,**d**): the wave height (\(H_{S}\)) and periods (\(T_{m\text{-}01}\)) and \(T_{m\text{-}(22)}\) (based on data in [105]). In other recent work, a mega project of data collection on the Arctic Ocean was initiated by researchers and consultants from Russia and United States. [PERSON] et al. [106] addressed their focus to several subjects, e.g., seismic data, sub-bottom profiler data, geological sampling, borehole drilling, gravity, magnetic anomalies, and offshore geodetic data. Various equipment setups were prepared in terms of the seismic data, such as bolt APG air guns, control, and the ORCA or QINSy monitor navigation system; the DigiSHOT digital air gun controller; the ION DigiSTREAMER solid-filled seismic streamer; and the ION DigiSTREAMER integrated offshore seismic data acquisition system. Furthermore, preparation for a sub-bottom profiler survey was conducted, including the acquisition of additional data by multi-beam and single-beam echo sounders.