# Detection of Underwater Targets Using Polarization Laser Assisted Echo Detection Technique
## 1 Introduction  
With the deepening of scientific research, the polarization characteristics of light were discovered, and laser polarization detection, a new laser detection technology, was proposed to become a powerful auxiliary technical means in laser underwater target detection technology with a broad application space. Polarization, as an inherent and independent property of light waves, also contains abundant information on reflection and scattering from an object's surface, which can improve the detection ability of object imaging. [PERSON] et al. [1] proposed a new light intensity-spectrum-polarization based bionic information fusion target detection method for the special underwater optical environment, which can get rid of the tedious image preprocessing process by adaptive feature fusion algorithm based on the obtained underwater optical a priori knowledge and achieve reliable target detection results at the cost of lower computational complexity. [PERSON] et al. [2] used a SALSA camera to obtain underwater polarization images under natural illumination, and studied the effects of different material objects, placement depth, milk concentration and waveband factors on the polarization imaging of underwater targets, and found that the blue band polarization imaging can better obtain the boundary contour of underwater objects and other information. The underwater polarization imaging technique developed by [PERSON] [3] and others from the polarization characteristics of the light field can effectively suppress the scattered light from the underwater background and use the polarization difference characteristics of the target information light and the scatteredlight from the background to effectively separate the two and achieve clear imaging. [PERSON] et al. [4] analyzed the corresponding polarization characteristics of target information light, backward scattered light and forward scattered light and targeted to solve the influence of different components on the image and thus realize the improvement of image quality. [PERSON] et al. [5] proposed a method to detect the wake of underwater targets by using infrared polarization wake with a low-orbiting satellite as a platform, combining laser dynamic depth measurement technology and polarization laser detection technology to achieve the detection and identification of underwater stealthy moving targets. [PERSON] [6] proposed a novel scheme for acquiring polarization information of reflected light from underwater targets based on the Stokes matrix representation and split-amplitude method and completed the research on the key technology of laser polarization diving detection by describing the working principle and implementation steps in the scheme, building the system, and analyzing the laser transmission attenuation energy. [PERSON] [7] researched the multi-scale decomposition method based on boosted wavelet transform for image fusion enhancement processing to improve the quality of polarized images in view of the problems of poor quality, blurred texture details and low contrast of underwater polarized images. [PERSON] et al. [8] carried out experiments on the detection of polarization characteristics of camouflaged targets and studied the relationship between observation angle, target surface roughness, material, etc. [PERSON] et al. [9] carried out experiments on polarization imaging technology to improve the imaging clarity and imaging distance by quantitatively calculating the clarity of the imaging image, the quantitative relationship between the clarity of the polarization image and the distance, and found that when the water quality is clear, the imaging effect of circular polarization is better than the imaging effect of linear polarization, and as the attenuation coefficient of the water body becomes larger, the imaging effect of linear polarization is better than the important conclusion of circular polarization.