A survey of maritime unmanned search system: Theory, applications and future directions

The rising frequency of ocean activities, such as ocean transportation and marine resources development, inevitably leads to a higher incidence of sudden accidents at sea. Maritime search and rescue (MSAR) plays a crucial role in marine transportation. Specifically, maritime search serves as a preparatory mission before executing the actual rescue operations. In 2018, the International Maritime Organization (IMO) made significant legal amendments to the international convention for the Safety of Life at Sea (SOLAS), emphasizing the critical importance of MSAR operations. Nevertheless, the conventional maritime search systems, such as independent surface ships, underwater vehicles, or aerial platforms, fall short of meeting the demands of modern shipping and can impose significant energy and economic burdens. Meanwhile, unmanned systems are gaining prominence in maritime search due to their notable advantages, including high efficiency, cost-effectiveness, and rapid deployment. One observes that the research of unmanned maritime search is still in an early stage. This paper provides a comprehensive survey of the state of the art of maritime unmanned search system development with four dimensions, including the unmanned aerial vehicle (UAV), unmanned surface vessel (USV) and underwater unmanned vehicle (UUV) and its cooperative heterogeneous vehicles. Firstly, the search types, the superiorities and the application scenarios of the unmanned search system are summarized. Then, the theoretical progress, engineering applications and limitations for the unmanned search system are investigated. To further discuss the advantages of the unmanned search system, a novel cooperative platform is established that uses an USV and two UAVs. In the proposed platform, the sensor, communication, guidance and control subsystems are described to illustrate the convenience and the effectiveness of the proposed cooperative system. Finally, the future research directions are examined to expedite the practical implementation of theoretical advancements in the field of maritime unmanned search.