The unique optical characteristics of the underwater environment, such as light refraction and loss of salient features, pose a significant challenge to traditional vision sensors, especially in the swarm operation scenario where multiple autonomous underwater vehicles (AUVs) cooperate with the mother ship for positioning. To address these challenges, this study proposes the application of soft constraints on mirror position to improve the robustness of optical target positioning in shallow water. During the mapping phase, we establish and optimize the pose relationships between ArUco markers and their mirrors, thereby expanding the locatable space for AUVs (Autonomous Underwater Vehicles) . With the arrangement of ArUco markers unchanged, the number of usable markers doubles. Surface mirror-assisted positioning provides more visual features and additional computed corner points, enhancing the reliability of camera observations and improving positioning accuracy. Experimental results demonstrate that, compared to classical algorithms from the Artificial Vision Applications (A.V.A) laboratory, our method improves position accuracy by 25.8% in single-marker scenarios and by 14.7% in multi-marker scenarios. Therefore, our method provides enhanced mapping and positioning for AUVs in shallow water areas where optical markers can be deployed. This study provides a new mapping paradigm and multi-body localization solution for optical marker-guided underwater swarm operations.

Aquatic organisms, due to soft body structure and high agility, have inspired many biomimetic robots. However, considering the issues of insulation and waterproofing, as well as the driving module of soft materials, their control systems are usually larger and heavier. Therefore, small underwater robots often tethered, i.e., it cannot integrate energy and control systems onto the body, which greatly limited in its working range and activity mode. This paper presents a small untethered bionic manta ray. The robotic fish is driven by dielectric elastomer actuators (DEA), which controls the double wing structure on both sides by the central muscle part to simulate the process of the manta ray’s lateral fins fanning to propel itself forward. And the flexible printed circuit board (FPC) constitutes the body of the fish and is also an independent energy control system. The electronic components are evenly distributed on the double-wing structure of the robotic fish to realize the integration of the energy control system. This circuit system can be powered by a small lithium battery and output a periodic voltage to drive the motion of the robotic fish. The masses of our tethered and untethered fish are 1.9g and 5.1g respectively. The swimming speed of these two types of fish can reach 42.5mm/s and 17.0 mm/s. And this design principle can be extended to the research and design of various flexible devices and soft robots.