Research on ship wake detection mechanism based on optical backscattering effect

摘要

The characteristic of an incident light beam scattered from underwater bubble cluster was investigated and a Monte Carlo model was employed to simulate the backscattered signal from bubbly wake by laser pulses. An optical ship wake detecting experimental system was designed and built, in which there was a frequency doubling and Q-switched YAG solid state laser adopted in the transmitter as the light source, and a telescope system with large limiting aperture and small field-of-view(FOV) in the receiver. A photomultiplier tube was employed as the detector while simulated bubbly ship as the detecting targets. The optimization of the system's parameters was studied in lab, the results showed that The influence of laser pulse energy and the FOV size of receiving optical system on the detecting effect was studied by experiments. The results showed that for near targets with small optical depth( τ < 1.4), the optimized Signal-to-Noise Ratio(SNR) is obtained using a laser with single pulse energy of 60mJ ~ 84mJ while for far targets with large optical depth( τ > 2.0), the optimized SNR is obtained using a laser with single pulse energy of 108mJ or above. Good detecting effect is achieved using a receiving optical system with the FOV of 4°.