High precision underwater 3D imaging of non-cooperative target with frequency comb

High-precision underwater imaging technology has an important role in underwater navigation and identifica-tion, underwater pipeline inspection, sinker docking, and underwater vibration measurement. Due to the different mechanisms of underwater measurement sources, such as 3D gated imaging and streak tube imaging, the accuracy of underwater target imaging can reach the millimeter level. In this paper, we propose a high-precision underwater imaging method based on frequency combs. When measuring the non-cooperative target underwater, the spectrogram is modulated due to the strong dispersion property of water. After that, for the gained spectrogram, we use two algorithms, i.e., center offset frequency and phase slope, to obtain the distance and imaging, respectively. By comparing with reference values, the underwater experimental results combining two algorithms show an agreement within 8 mu m in the range of 2.5 m, corresponding to 3.2 x 10(-6) relative precision. This work can provide a strong guarantee and support for high-precision underwater applications.