Underwater microbubbles detection and identification based on dark field imaging

Abstract

An underwater microbubbles detection and identification method based on dark field imaging is presented, focusing on measurement of the characteristics of microbubbles with high-resolution image capture. The target microbubbles in sampling volume of interest are illuminated by a laser sheet, which is matched with the depth of field. Images are captured in-focus under an observation angle of 90 deg to implement dark field detection, which suppresses the influence of interferential light, such as backlighting, scattering light, and blur caused by defocus. In this configuration, we propose to measure bubble size based on the distance of peak values of two glare points formed by the diffraction and reflection lights. The modified Resnet18 is employed to recognize the bubble images, and the number of bubbles with different diameters in bubble images is counted by template matching. Experimental results show that this dark field configuration allows high resolution imaging and evaluation of the diameter scale of the microbubbles. The precision of bubble recognition and quantification of bubbles within a certain range achieves more than 90%.