# Method for Detecting Underwater Microbubbles Using Dual-Mode Fusion of Laser Polarization
## 1 Introduction  
There are a lot of bubbles in the marine environment because of things like ship navigation, breathing marine life, and breaking waves [1]. A technique that has been widely employed in the detection and acquisition of marine environmental information, the analysis of marine biological activity, the recognition of ship track heading, and other elements is examining the variations in the features of different bubbles in seawater [2]. As a result, the ability to detect bubbles in saltwater is crucial to human ocean exploration and management. Optical detection techniques are commonly employed to identify bubble attributes (e.g., bubble size distribution, bubble number, etc.) because bubbles are good light scatterers [3]. When compared to the single data source of traditional optical radiation measurement, which only provides intensity information and makes it difficult to perceive changes in the size and number of bubbles [4], and the low quality of traditional image detection, which is based on the polarization difference of different targets and can reduce the influence of medium scattering and accurately distinguish between bubbles and impurity targets [5], active polarization imaging is one of the best ways to generate crisp underwater bubble images because it uses the polarization difference of various targets to minimize the impact of medium scattering and accurately distinguish between bubbles and other targets [6]. However, the optimal imaging region of active polarization imaging is significantly reduced, as is the detection performance, in scenarios like the uneven light intensity in the imaging region caused by multiple scattering of seawater particles, the \"polarization camouflage\" formed by marine plankton absorbing polarized light, and the mixed stack occlusion of bubbles and impurities. These factors make it challenging to quantitativelydetect the size and quantity distribution of bubbles by polarization imaging [7]. Therefore, it is of great theoretical and practical significance to study the technology of bubble image enhancement under non-uniform light conditions and bubble feature recognition under complex water quality conditions. Underwater bubbles have been extensively studied by numerous academics. Because of their small particle size, these bubbles are challenging to recognize, detect, and extract the properties of light scattering intensity from. In order to measure the features of bubble groups, [PERSON] et al. [8] suggested using laser imaging, and [PERSON] et al. [9] created an experimental apparatus that used polarized light scattering to identify casein bubbles that were both monodisperse and double-disperse. Nevertheless, the technique is challenging to modify for the dynamic ocean environment, and the two researchers mentioned above only observed bubble particles in static settings. [PERSON] et al. [10] proposed a method using trained convolutional neural networks (CNNs) to segment overlapping bubbles for identification. [PERSON] et al. [11] designed a polarization descattering imaging method based on a genetic algorithm to enhance image features. However, the scheme proposed by the two scholars is not suitable for underwater objects with different polarization characteristics in the imaging scene and the recognition of weakly polarized targets such as bubbles, and it is difficult to distinguish the stacking of bubbles and impurities. [PERSON] et al. [12] analyzed the relationship between the polarization-gated imaging effect and refractive index at a specific scatterer scale. Meanwhile, [PERSON] et al. [13] used a Monte Carlo simulation and quantitative experiment to study the influence of continuous particle size change on polarization imaging. However, the above method struggles to detect the compound change in bubble number and size characteristics. [PERSON] et al. [14] proposed a visibility enhancement method using transmittance correction to realize underwater imaging of objects with different polarization characteristics. [PERSON] et al.