Enhanced Underwater LiDAR via Dual-Comb Interferometer and Pulse Coding.

Underwater distance/length sensing serves as a fundamental function and plays a crucial role in a wide range of applications, including topography and geomorphology in remote sensing. Advanced light detection and ranging (LiDAR) systems and algorithms are significant for underwater tasks, such as objection positing, target searching, and rescuing. In this paper, we propose a dual-comb interferometer-based LiDAR system to achieve accurate underwater absolute distance measurement. Specifically, the system applies a well-designed pulse coding strategy that significantly expands the non-ambiguity range for underwater distance measurements, allowing for precise long-distance measurements in a single attempt. Besides, we introduce a correction process to handle the water group refractive index problem. Compared with reference values, experimental results show that the range fluctuation is within ±15 μm at a 12 m measurement range, and the Allan deviation is 0.62 μm over an averaging time of 100 s. In practice, this LiDAR solution with a micrometer-level precision is promising for various applications in ocean engineering.