Underwater imaging system identifying 10 μm～500 μm wake bubbles

Considering the difficulties in the wake bubbles imaging, a wake bubbles measurement system was presented based on the combination of high speed photography and laser sheet scanning technology. In this system, laser sheet was used to illuminate the wake zone to avoid the image stacking of bubbles. Because the particle size of bubbles was in a wide range(10 m～500 m), three switchable magnification lenses were designed for the bubbles imaging. Lenses were split into front and rear groups, with parallel rays transmitting between them. With the sweeping of laser sheet, the image information of bubbles in a volume could be sampled. Moreover, by keeping the front group moving synchronously with the laser sheet, bubbles could always image clearly when the laser sheet swept. The influence on image quality, the determination of laser sheet thickness and the system distortion correction, when laser sheet swept, were also discussed. The systems conducted a sea test at No. 760 institute of China ship building industry corporation(CSIC), the depth of the sea was 5 m,10 m～2 000 m bubbles step from objective test ship, the test results show that the image quality is good and this system satisfies technical requirements.