## 9 Concluding Remarks  
Reviews on several aspects of sensor-based instruments and apparatus were performed in this work, including offshore engineering, ocean state, marine structures, and polar territory. According to the comprehensive review of the mentioned areas, sensors serve as a vital tool for measuring physical phenomena and observing environmental conditions. Several essential remarks are summarized as follows:  
1. In terms of logistic and shipping activities, sensors are heavily involved to ensure that the pathway and sailing route of a ship/vessel are correct and clear to avoid collision or other accidents. The frequently used tools include high-resolution satellite imagery, enhanced spatio-spectral techniques, multi-polarization synthetic aperture radar (SAR), multilayer fusion light-head detectors (MFLHDs), and multiscale Wasserstein auxiliary classifier and generative adversarial networks (MW-ACGANs). These were then varied into global navigation satellite systems (GNSSs), inertial measurement units (IMU)s, Doppler velocity log (DVL), spectral entropy (SE), and C0 complexity in early 2021. 2. The hydrodynamic characteristics of marine design and structure are critical aspects that need to be accurately estimated. A sensor-based instrument is recorded for six degrees of freedom, resistance/drag, and propulsion performance. As concluded from the review, the subject of investigation is not only conventional ships, but also vessels with special purposes, i.e., cruise ship, sailing yacht, and underwater cleaning robot. It was also noted in certain works that sensors are deployed for measuring noise in the underwater territory. This contributes to an effort to quantify the effect of noise radiation on mammals' communication waves. 3. Regarding ship/vessel design, energy-saving characteristics have been assessed on machinery monitoring systems. Methodologies for designing sensors and measuring this phenomenon include first-principle safety analysis, hazard and operability studies (HAZOP), fault tree analysis (FTA), wireless sensor network (WSN), structural risk assessment (SRA), machinery risk assessment (MRA) tools, acoustic emission sensors, and laser heads clocked at 16 MHz. The evaluation of vibration interference in recorded motion data in the ice field territory is the interdisciplinary research of this field (hydrodynamic) and the polar science field. 4. Besides hull performance, machinery safety must also be evaluated from a sustainability point of view to either avoid loss in fuel consumption or environmental pollution. The summarized research indicates that machinery safety does not solely concern machine performance, but also concerns refraining the subject from undergoing physical damage (e.g., collision damage, hull joint failure, and unpredicted behavior of  
Figure 36: Influences of the deployed GA types on the success rate [148]. anisotropic material). Therefore, the collision avoidance concept has been necessarily developed based on the beam search algorithm (BSA), followed by the deployment of laser vibrometry and a displacement laser sensor to quantify defects on the hull joint. In the case of anisotropic materials, a study was performed on polymer composites using acoustic emission Kolmogorov-Sinai (K-S) metric entropy. * Exploring the Arctic territory is the most addressed concern in terms of polar science and arctic engineering using sensor-based apparatus. For the past decade, works in this field have been dominated by the dedication to observing environmental conditions (of the ocean, atmospheric, and tundra areas), primarily when climate change arises due to an excessive amount of fossil fuel consumption. In recent years, the study has extended to evaluate problems such as the ice melting phenomenon. This work has been carried out especially near Canada and Greenland. Furthermore, autonomous frequency-modulated continuous-wave (FMCW) radar has been used to measure states of snowpack and ice levels.