Underwater visual inspection and measurement using optical holography

Abstract

In offshore oil and gas exploration, visual inspection and measurement often has to be carried out under conditions of poor visibility and at great depths. Recording a hologram of an underwater scene with its subsequent replay in the laboratory could provide enormous benefits to the inspection engineer. When replayed in the real image mode, dimensional measurement may be performed directly on the image formed in real space using, for example, measuring microscopy or TV cameras. Potential applications include general archiving, measurement of corrosion pitting and cracking, examination and measurement of damage sites, structural profiling and examination of marine growth. In this paper, we outline the general concepts of underwater holography. A résumé is given of the work undertaken in the past, the problems experienced and their solution and an indication of our general direction leading to the establishment of holography as a unique method of subsea inspection.