Sea Technology

SEP 2017

The industry's recognized authority for design, engineering and application of equipment and services in the global ocean community

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Page 29 of 68 September 2017 / st 29 W ith the aging of oil and gas installations, requests for inspection and control of components are increasing rapidly in the industry to prevent failure, and some inspec- tions need 3D as-built surveys before modifications can be done on an installation. Optical measurement technologies have been used over the years for above-water surveys, while photogrammetry and laser scanning have been introduced into the subsea environment only recently. The main challenge for any kind of subsea survey is stability; even placing a tripod on the seabed might not be a stable option due to ocean currents. Photogrammetry provides the ideal solution: Not only is stability not an issue, but movement is actually required in order to get pictures from different angles. Moreover, thanks to the development of HD cameras, it is now possible to shoot vid- eo and extract high-quality images instead of shooting only still pictures. HD Cameras The history and development of photogram- metry is linked to the development of cameras. Some cameras have been developed specifical- ly for photogrammetry to be able to conduct ac- curate measurements on the images. These are called metric cameras. Measuring in this way requires doing at least three things: keeping the flatness of the film by adding a pressure/vacuum device; adding marks on the film fiducials in or- der to correct the optical distortions; and keep- ing the relative positions between the lens and the film as rigid as possible. In 1994, the development of the first digital cameras marked the beginning of a new era, ushering in broader use of photogrammetry in various industries and the develop- ment of new processes and new methodologies. Logically, the development of cameras in order to be able to con- duct measurements from images led to the development of CCDs (charged-couple device) sensors, pixels and software. Whereas it was difficult, if not impossible, to build a perfect- ly mechanical and optically stable camera, it seemed pos- sible to correct all deformations by software, for example by working on camera self-calibration routines, which meant it was just a matter of waiting for the development of better cameras with better resolution and stronger optical and me- chanical characteristics. Introducing these cameras to the subsea environment was then only a matter of creating the right canister and developing a communication interface suitable for ROVs. A typical example of such a camera is the 1Cam HD camera by SubC Imaging, which is broadly used now for subsea visual inspection and subsea 3D surveys. 3D Subsea Survey On the Fly VLS Uses Laser, Camera for Point Cloud Surveying By Arnauld Dumont (Top) DimEye VLS system for divers. (Bottom) Dim- Eye custom VLS system for subsea applications.

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