Journal of Marine Science and Engineering

Search and Rescue (SAR) operations are conducted to locate and safely rescue individuals or objects in distress as rapidly as possible following maritime emergencies. In this process, operational performance depends not only on determining the target’s probable location but also on the specific search pattern used to scan the search area. The aim of this study is to develop alternative search patterns to the parallel and expanding square search patterns used within the International Aeronautical and Maritime Search and Rescue (IAMSAR) methodology. To this end, Hilbert, Moore, Morton, V-formation, pentagonal, hexagonal, octagonal, and spiral search patterns were mathematically defined and rendered for algorithmic implementation. The patterns underwent a three-stage evaluation process. The first stage assessed baseline performance independently of external factors; the second stage evaluated behaviour under different initial target locations; and the third stage assessed target detection performance for five distinct types of drifting targets under varying wind, current, and search area conditions. The results revealed that the Moore pattern achieved the highest number of fastest target detections in the parallel search group, followed by the Hilbert pattern, while the Morton pattern stood out in terms of second-fastest detection counts. In the expanding square search group, the spiral pattern achieved the highest number of fastest target detections, followed by the hexagonal and expanding square patterns, while the expanding square pattern ranked first in second-fastest detection counts, followed by the octagonal pattern. However, the relative performance of the patterns varied depending on search area size and environmental conditions. The study’s primary contribution is treating search pattern selection as an independent SAR planning variable, offering viable alternatives to IAMSAR patterns, and establishing a reproducible, extensible framework through mathematical and algorithmic definitions that can be used in future optimisation, decision support, and area-scanning initiatives. In doing so, the study frames the question “which search pattern can most effectively cover the designated search area?” as a systematic research problem alongside the fundamental SAR question: “Where should the target be searched for?”

This paper investigates the robust course control for marine surface vehicles (MSVs) by using reinforcement learning and a dynamic event-triggered mechanism under rudder faults. A fault-tolerant optimized tracking control scheme is designed based on reinforcement learning. Firstly, a general actuator fault model is established. Secondly, internal and external disturbances as well as fault dynamics are aggregated into lumped uncertainties, and a fault observer is constructed to estimate and compensate the lumped uncertainty term. Then, a tracking cost function for the MSV system is constructed, and a reinforcement learning framework with a single critic network is used to approximate the value function and generate a learning-based compensation input. Finally, a dynamic event-triggered mechanism is implemented between the control layer and the execution layer to reduce the triggering frequency of actuators. Lyapunov stability theory is utilized to prove that all signals within the closed-loop system are uniformly ultimately bounded. Simulation results verify that the proposed control scheme achieves favorable overall performance.

Microplastic (MP) transport through the deep ocean remains poorly constrained, particularly regarding particle morphology and water-column biogeochemistry. We quantified MP abundance concentrations in the water column, expressed as items/L, and sedimentary MP inventories, expressed as items/kg dry weight (dw), in two full-depth profiles to 5650 m and characterized MP inventories in surface sediments from 33 stations in the western Pacific Pigafetta Basin. MPs occurred throughout the water column (0.7 ± 0.4–7.9 ± 2.8 items/L; mean, 3.0 ± 1.5 items/L) and generally decreased from euphotic to abyssal and bottom waters. Apparent oxygen utilization maxima and enhanced nutrient regeneration occurred at 800–1000 m, whereas MP abundance was negatively correlated with apparent oxygen utilization and potential density. This pattern is consistent with changes in MP-associated carrier phases and suspension states rather than local accumulation within the remineralization maximum. Fibers and fragments dominated the water column, while surface sediments contained relatively more fibers and smaller particles, indicating compartment-level differences in morphology and size. Sediment abundance ranged from 6.5 to 180.1 items/kg dw. A conservative, Fourier-transform infrared spectroscopy (FTIR)-constrained, morphology-resolved free-particle settling model estimated a mean sinking velocity of 17.6 m/d and a modelled free-particle vertical transport potential of 2.82 × 10⁴ items/m²/d, with non-fibers contributing 87%. This transport potential is distinct from depositional flux and burial flux, neither of which was directly measured in this study. These modelled values represent transport potential under specified free-particle assumptions and are not direct measurements of depositional flux, burial, or long-term sequestration. The results identify morphology-dependent settling and carrier-phase transformation as processes that may influence the distribution of MPs between the water column and surface sediments.