Research On Laser Detection Principle Of Wake Profile

The technique for detecting and tracing the underwater object such as fish stocks or ships, based on optical properties of wakes, breaks the conventional way of using sound field, but uses light wave as the information carrier, which makes the conventional acoustics disturbance and the countermove useless. Besides it has farther detection distance, higher hit probability and non-interference of electromagnetic noise or ambient noise. In this dissertation, 532nm laser is used as information carrier, and the feasibility of detecting wake profile by laser is demonstrated. Particularly, calculations on light scattering by bubbles in the absorbing sea water, laser detection device design of wake profile and laser detection principle of wake profile are concered. In this dissertation, achievements in the theoretics and experiments are as follow.In the theoretical study, using Mie theory, single-scattering properties of a clean bubble and phase functions of bubble populations for wakes in the absorbing sea water are calculated. The method that wake bubbles may be effectively detected is theoretically estimated, which provides the theoretical base for the feasibility of detecting wake profile by laser.In the experiment, designing laser detection device of wake profile. The bubble backscattering at 180°is measured using the monostatic optical geometry.Based on above method, Two-dimensional of proper motion design scan over the wake region is realized using an angular scanning system. The monostatic optical geometry are composed of 45°holophote having 5 mm aperture and scanning system, two kinds propellers are designed and driving system of warship, generating a simulation within the laboratory. Furthermore, acquisition card application and signal treatment procedure are compiled.In experimental research, laser detection principle of wake profile. Firstly, laser detection device of wake profile is debuged, and then the best location of wake profile is seeked. Secondly, wakes produced by two kinds of propellers with different sizes at two kinds of the rotation speed are simulated using this laser probing device. Thereinto, wake profiles, bubble scattering intensities and bubble distributions with velocity and size are mainly focused, and influences of the rotation speed and size of the propellers on those wake features are discussed. At the meantime, the method to distinguish the wake and non-wake region is presented, and thus wake profile is detected by laser. Finally, the experiment repeatability of the laser detection device is tested.