Abstract: Aiming at the deep sea equipment suspension installation used in marine engineering, the multi-camera video motion analysis method is used to calculate the underwater three-dimensional motion trajectory, guiding the structural installation of the ocean engineering and analyzing the underwater motion features of the equipment. The processing of underwater video and image acquisition are facing a number of challenges. Firstly, due to the large amount of suspended matter and particles in the underwater environment, the light is scattered under water, which causes the underwater image to degenerate. Secondly, a major obstacle which underwater video motion analysis encounters is the image error caused by the refraction of light. Since the light is refracted among different media like water, glass and air, and the optical path is curved, the camera imaging model on land is no longer suitable for water use and a new underwater camera imaging model is called for. With a focus on the internal parameter and external parameter calibration method of underwater cameras, this study proposes an algorithm for calculating the three-dimensional trajectory of underwater moving objects and introduces an underwater camera imaging model with ray refraction. The underwater target motion video which is photographed by three underwater cameras fixedly arranged is proposed to calculate the 3D trajectory of the underwater target. This method is suitable for large-scale movement of underwater objects in a pool environment, and a relatively accurate trajectory can thus be obtained. The proposed method for measuring the underwater target motion trajectory is experimentally verified in the pool environment.

Key words: underwater camera calibration, three-dimensional trajectory, visual measurement