Underwater De-scattering Imaging by Laser Field Synchronous Scanning

Abstract

A novel underwater optical imaging method is proposed to improve the quality of images which suffer from poor visibility due to underwater scattering and signal attenuation under artificial illumination. A high sensitive sCMOS video camera was designed to operate in rolling shutter mode which formed a narrow field-of-view (FOV) during the exposure process. Meanwhile, a MEMS-based two-dimensional laser scanning light source only illuminated the camera's narrow FOV. Thus the backscatter caused by the FOV intersection of the camera with the light source was reduced. Since the laser scanning route of the method is a field instead of a line, we named it Laser Field synchronous Scanning (thereafter LFS). A modified off-the-shelf laser scanning projector with green laser diode driving signal extracted was employed as the two-dimensional laser scanning light source, and the driving signal was received by the sCMOS video camera to synchronize the rolling shutter. The experiment was conducted by utilizing contrast ratio and contrast signal-to-noise ratio (CSNR) to compare the images captured using an LED light source and LFS under different water turbidity. The experimental results show that LFS has much better contrast and CSNR performance compared to the LED light source, and the peak contrast improvement is 8.77 times (under 29.17 FTU) and the peak CSNR improvement is 1.87 times (under 17.72 FTU). The experiment results demonstrate that LFS imaging method can significantly reduce the backscatter effect caused by water and suspending particles under artificial illumination.