基于Stokes矢量的实时偏振差分水下成像研究

偏振差分水下成像能够有效地克服光散射效应造成的图像退化问题, 在水下物体探测与识别领域具有重要应用价值. 传统的偏振差分方法靠光学检偏器的无规则机械转动来实现对散射背景的共模抑制, 限制了其在水下成像过程中的实时探测性能. 本文通过分析偏振差分探测原理来建立偏振差分成像模型, 从理论上提出了基于Stokes矢量的计算偏振差分水下实时成像系统, 并进行了实验验证. 研究结果表明, 基于Stokes矢量的计算偏振差分成像不仅与传统的偏振差分方法具有相同的水下探测效果, 更重要的是可以实现快速成像过程. 该方法可以应用到目前的偏振成像仪器系统, 实现无需人-机互动的自动化实时偏振差分水下成像, 进一步提高水下物体探测与识别的效率.

Real-time polarization difference underwater imaging based on Stokes vector

Polarization difference imaging technique can effectively solve the underwater image deterioration problem that is caused by the interaction between light and water. Therefore, it has a significant application value in detecting and recognizing underwater target. In a traditional polarization difference imaging system, the object image is carried out by the common-mode rejection of background scattering light. However, the polarization state of the background scattering light is unknown, so the polarization difference imaging is realized by the irregular mechanical rotation of the optical polarization analyzer with two orthogonal polarization orientations. Therefore, it needs more time to determine the optimum detection angle of the polarization analyzer and cannot perform real-time underwater imaging, which restricts the rapid detecting function in the process of underwater imaging. In this paper, the detection principle of underwater polarization difference imaging is considered to exploit the difference in the polarization angle between background scattering light and target light. According to Marius's law, the physical model of polarization difference imaging is that the common-mode rejection of background scattering light will be achieved when the angles between the vibration direction of background and the two orthogonal polarization orientations are 45°. Because the Stokes vector can be used to express the polarization angle of light, we propose the principle and construction of a computational polarization difference imaging system for real-time underwater imaging by incorporating the Stokes vector into the established model. It replaces the mechanical rotation of the polarization analyzer in a traditional polarization difference imaging system with the information processing of the Stokes vector. The experimental results show that the proposed method not only has the same effective performance as the conventional polarization difference imaging compared with the regular imaging, but also can improve the blurred imaging performance caused by an underwater scattering effect as well as increase the underwater detection distance. This method realizes rapid underwater target detection and recognition because it saves a large amount of time compared with the traditional one. Further, if we combine this method with the current polarization imaging instruments that capture the Stokes vector instantaneously, then a real-time automatic underwater polarization imaging can improve the efficiency of the underwater target detection and recognition. These findings are helpful for designing and developing the underwater polarization difference imaging systems.