Smart Sensor Systems, SINTEF Digital, Forskningsveien 1, 0314 Oslo, Norway.
Sensors (Basel). 2019 Mar 1;19(5):1043. doi: 10.3390/s19051043.
High-precision underwater 3D cameras are required to automate many of the traditional subsea inspection, maintenance and repair (IMR) operations. In this paper we introduce a novel multi-frequency phase stepping (structured light) method for high-precision 3D estimation even in turbid water. We introduce an adaptive phase-unwrapping procedure which uses the phase-uncertainty to determine the highest frequency that can be reliably unwrapped. Light scattering adversely affects the phase estimate. We propose to remove the effect of forward scatter with an unsharp filter and a model-based method to remove the backscatter effect. Tests in varying turbidity show that the scatter correction removes the adverse effect of scatter on the phase estimates. The adaptive frequency unwrapping with scatter correction results in images with higher accuracy and precision and less phase unwrap errors than the Gray-Code Phase Stepping (GCPS) approach.
高精度水下 3D 相机是实现许多传统水下检测、维护和维修（Inspection、Maintenance、Repair，简称 IMR）操作自动化的关键。在本文中，我们介绍了一种新颖的多频相移（结构光）方法，即使在混浊水中也能实现高精度的 3D 估计。我们引入了一种自适应相位解缠过程，该过程使用相位不确定性来确定可以可靠解缠的最高频率。光散射会对相位估计产生不利影响。我们提出使用非锐化滤波器和基于模型的方法来去除前向散射的影响，并去除后向散射的效果。在不同浊度下的测试表明，散射校正可以消除散射对相位估计的不利影响。具有散射校正的自适应频率解缠可产生比格雷码相移（Gray-Code Phase Stepping，简称 GCPS）方法更准确、更精确的图像，且相位解缠错误更少。
