Underwater visual position measurement system for high-accuracy beam installation

In order to improve the efficiency of an underwater beam installation process, a computer-controlled position adjustment system is established. High accurate underwater position measurement is required in the system to ensure the fitting accuracy of two beams in the fine adjustment. This paper presents a visual measurement method using two pairs of underwater bi-camera vision system. Because the beams are of large size, appropriate markers as the measuring objects are coated on the rails fixed on two beams. A tank filled with clear water is put in front of each underwater camera to reduce the backscattering effect caused by turbid water. In order to solve the inaccuracy of position measurement due to blur edges and unclear contours on the images from the underwater cameras, super resolution as well as other image processing methods has been applied. By analyzing the extracted features from some interest lines and points of the processed images of markers, the position of the beam can be obtained. Results have shown that the position measurement errors are acceptable and the method can be used practically.