Design of Deep-Sea Imaging Sonar System With Universal-Scene Sparse Array

Imaging sonar plays a critical role in deep-sea exploration and surveying tasks, with miniaturization and high precision being the developmental trends. Traditional designs often focus on adopting sparse arrays to reduce system complexity but fail to consider the challenges posed by nonideal underwater environments, especially the degradation of sonar images caused by varying sound velocities and defocusing, along with the harsh requirements for hardware design imposed by extremely high water pressures. To address this issue, we propose a novel design of a deep-sea imaging sonar system with a universal-scene sparse array (USSA). At the algorithmic level, we propose the USSA and introduce a novel simulated annealing energy function that enhances beamforming performance in both far-field and near-field conditions across a wide range of sound velocities, achieving at least a 3.21 dB reduction in the highest sidelobe in the near field compared to traditional methods. Simultaneously, we propose a velocity-based direct image correction method, which can directly rectify sonar image distortions caused by mismatches between the actual and expected sound velocities, and the structural similarity index measure (SSIM) is improved by at least 5.1%. In terms of hardware, to accommodate the algorithm’s pursuit of universal-scene applicability, we propose a field-programmable gate array (FPGA)-based hybrid system architecture and a pressure-tolerant design. This hardware system features reconfigurability and enhanced universal-scene adaptability, providing a reliable platform for algorithm implementation. Based on these concepts, we fabricated a prototype. During a sea trial in the South China Sea, the prototype mounted on a deep-sea crawler and deployed at a depth of 4098 m under the sea, produced satisfactory images.