Laser detection method of ship wake bubbles based on multiple scattering intensity and polarization characteristics

Abstract

It is the research foundation of ship wake detection by laser and new-generation optical homing torpedo to investigate the influence of multiple scattering effect on light scattering intensity and polarization characteristics of the ship wake bubbles. The simulation model of laser back-scattering detection by ship wake bubbles is based on vector Monte Carlo method, and the multiple scattering mechanism is studied. The influences of multiple scattering effect and the bubble density in ship wake on the light scattering intensity and polarization characteristics of echo signal are analyzed. The echo photon polarization contribution reception method and the echo signal polarization statistical method are proposed to solve the problem that the low photon return probability cannot form the echo energy in the system with small receiver field of view. These methods are based on the basic idea of the particle collision importance sampling and the traditional energy receiving method. The polarization detection experimental platform for the simulated wake bubbles is built and the accuracy of the simulation results is verified in experiment. The consistence of the experimental and simulation results shows that the bubble distance and density information can be characterized by echo intensity, polarization information and the echo signal intensity, and the polarization characteristics can be used to detect and distinguish the ship wake bubbles, or even a low density wake bubbles with high precision.

Polarization Reconstruction Algorithm of Target Based on the Analysis of Noise in Complex Underwater Environment

“…We use the focal plane polarization camera to take data acquisition, the camera can obtain four intensity images at different polarization direction at one-time, I0, I45, I90, I135 respectively, and can obtain Stokes vector of target reflection and backward scattering light after passing through water at the same time. This paper uses method of curve fitting to obtain the best image of orthogonal polarization, taking Stokes vector and fitting out the curve of relationship between I(θ) and θ, using Equation (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19) to compute the corresponding figure of maximum intensity I max with angle is θ max and figure of minimum intensity I min with angle is θ min .…”

“…In an underwater environment, because the forward scattering mechanism are more complicated, the influence extent of backward scattering is greater than the forward scattering this article does not take the forward scattering factor into subsequent process of modeling, and specific content can refer to Section 2. According to Equation (3-2), the maximum intensity expression and minimum intensity expression are shown in Equation (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20):…”

“…Using Equation (3-20) can get intensity expression of underwater scene as shown in Equation (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21):…”

“…Similarly, we can obtain the reflection coefficient and refraction coefficient expression of the polarized component expressed by S. The theoretical calculation shows that the light intensity on the bubble interface decreases continuously with increasing transmission time, and for the fourth reflection and refraction cycle, the intensity of refracted light of bubble tends to zero [16]. The value of DOP increases with increasing transmission frequency, and at the interface in the fourth transmission cycle, DOP of refraction and reflection light is the largest, being converted to almost completely polarized light [17].…”

“…Fresnel law indicates that the reflectivity and transmissivity are connected with the polarization and incident angle of incident light and the refractive index of the medium. Any polarization of light can be decomposed into a pair of mutually perpendicular components, a vibrating direction perpendicular to the plane of incidence, expressed as S, and another vibrating direction parallel to the plane of incidence, expressed as P. According to [17] the Fresnel formula, we can obtain the reflection coefficient and the refraction coefficient expression of the polarized component expressed by P . Similarly, we can obtain the reflection coefficient and refraction coefficient expression of the polarized component expressed by S. The theoretical calculation shows that the light intensity on the bubble interface decreases continuously with increasing transmission time, and for the fourth reflection and refraction cycle, the intensity of refracted light of bubble tends to zero [16].…”