Underwater Laser Triangulation Sensor Model With Flat Refractive Interfaces

Underwater 3-D measurement has many applications, for example, in the oil and gas industry, archeology, and biology. Systems with laser triangulation sensors (LTSs) are being currently used underwater, even though they face some strong environment influences. Among these challenging influences are poor image quality and refraction, due to optical window interfaces between water and air inside the camera chamber. The refraction effect can be modeled knowing the distance from the camera pinhole center to the surface of refraction, the axis of refraction, the refractive index of the mediums, and the thickness of the optical window. This paper analyses a method for underwater LTS measurement using real experiments. The proposed method is based on the pinhole camera model, a refraction modeling, and a fitted mathematical plane for the projected laser light plane. After the in-air calibration, a step standard is measured underwater and the window distance from the camera is optimized. The method is evaluated according to guidelines for optical systems evaluation (VDI/VDE 2634).