Visual measurement method for three-dimensional shape of underwater bridge piers considering multirefraction correction

Underwater structure inspection faces great challenges because of the poor measuring environment. To conduct health monitoring for underwater bridge piers, this paper describes a method mainly composed of multicamera digital image correlation, a multirefraction correction model and an approach of grayscale mapping. Verification tests were carried out to examine the accuracy of the reconstruction results both in air and water, and the effectiveness of the multirefraction correction model was also proven. An underwater measuring system was built and was successfully applied to measure the round surface of a concrete pier underwater. The axial measurement error of the points reconstructed after multirefraction modification under the cylindrical coordinate system was only 1.58% of the diameter of the bridge pier. Furthermore, the gray information was transferred to the three-dimensional point cloud. This paper may promote the detection efficiency and accuracy of underwater bridge pier health monitoring.