Long-Distance Underwater Target Search and Localization Using an AUV With Chemical Sensing

With the increasing reliance on global air and sea transport, the need for effective underwater search mechanisms is becoming more pressing. However, complex marine environments presents substantial challenges for the recovery of crashed aircraft or sunken vessels. Existing underwater search methods rely heavily on acoustic communication, which is constrained in both range and energy. Although molecular communication offers considerable promise, there is a lack of search algorithms applicable to underwater scenarios. Therefore, we propose the hexagonal inverse gradient search (HIGS) algorithm for the search mission of lost objects underwater. HIGS employs the autonomous underwater vehicle (AUV) that navigates using molecular concentration gradients. To overcome the challenge of nearly zero-gradient regions, we develop a set of three-dimensional motion rules based on real-time chemical sensing, allowing AUVs to adjust their trajectories adaptively. Additionally, a zero-gradient escape strategy is incorporated to prevent the AUV from becoming trapped in local optima within complex underwater environments, thereby ensuring persistent and effective target search. Simulation results confirm the effectiveness of the proposed algorithm in underwater search missions.