Polarization difference imaging can improve the quality of images acquired underwater, whether the background and veiling light are unpolarized or partial polarized. Computational polarization difference imaging technique which replaces the mechanical rotation of polarization analyzer and shortens the time spent to select the optimum orthogonal ǁ and ⊥axes is the improvement of the conventional PDI. But it originally gets the output image by setting the weight coefficient manually to an identical constant for all pixels. In this paper, a kind of algorithm is proposed to combine the Q and U parameters of the Stokes vector through pixel-level image fusion theory based on non-subsample contourlet transform. The experimental system built by the green LED array with polarizer to illuminate a piece of flat target merged in water and the CCD with polarization analyzer to obtain target image under different angle is used to verify the effect of the proposed algorithm. The results showed that the output processed by our algorithm could show more details of the flat target and had higher contrast compared to original computational polarization difference imaging.
When light travels in water, the state of polarization of the incident light changes as the photons are scattered with suspended particles or reflected on the target surface. In order to increase the working distance, underwater polarized light imaging (UPLI) technology usually makes use of the different depolarization effect between the water body and target on the incident polarized light to filter the backscattered light. So it is significant to study the depolarization characteristics of polarized light in water. In this paper, a Field Monte Carlo (EMC) program is developed to simulate the transmission characteristics of polarized light in water with specific particle and attenuation coefficient. EMC method is different from the traditional Monte Carlo method which tracks the Stokes vector of the beam. It uses the Jones mechanism to characterize the polarization state of the photons. By tracking the two vertical components of the photonic vibrating electric vector, the polarization state and the depolarization effect of polarized light transmitted through a body of water can be obtained. The simulation results are based on horizontal polarization, vertical polarization, 45 degree linearly polarized light(LPL) and right circularly polarized light(CPL) as incident light , Stokes vectors of four types of received light is obtained respectively, and the related parameters are calculated to analyze the polarization memory performance. The numerical results show that water body have good polarization memory property and the influence of the particle size and the attenuation coefficient on the LPL is obvious than that circularly of the polarized light, and the CPL has better polarization memory ability.