Sea Technology

APR 2014

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30 st / April 2014 www.sea-technology.com improved bathymetry system for pipe spanning and straightness measure- ments. In 2009, in conjunction with Woods Hole Oceanographic Institution, C&C developed a proprietary camera and fash system to support the acquisition of photo images from a target altitude of 8 to 10 meters. The goal was to pro- vide pre/post-lay pipeline route im- ages/movies and/or wide-area mosaics for arch, geohazard surveys. To date, this system has been used by multi- ple oil and gas and academic clients worldwide for various projects, includ- ing mapping shipwrecks, large-area mosaics of seafoor anomalies and pro- posed pipeline pre-lay images. When combined with the high accuracy of the INS onboard the AUV, pipeline ex- pansion/movement measurements are supportable with a high level of repeat- ability. At a standard survey altitude of 8 meters, it supports detection and identifcation of events on a pipeline of 1 centimeter by 1 centimeter. In 2010, C&C outftted its line of C-Surveyor AUVs with a geochemical sensor suite in support of detection and mapping of seeps and leaks. The addi- tional sensor suite consisted of the fol- lowing sensor instruments: CH 4 , CO 2 and PAH. These sensors are in support of leak detection during an inspection. The third and fnal component for the upgrade to support pipeline inspection involved the multibeam echo (MBE) system. On a standard C- Surveyor, the MBE is a Kongsberg EM 2000. Its specifcations are: 200 kilo- hertz, 150° swath, 111 beams and a 1.5° by 3.0° beam pattern. The EM 2000 is a wide-area survey tool, but it is not an ideal bathymetric tool for supporting pipeline inspec- tion tasks, such as top-of-pipe picking for spanning analysis. Its sparse beam spacing and large beam footprint are not ideal for pipe detection and mea- surement. An extensive two-year search for its replacement resulted in choosing both a standard MBE system and a unique laser bathymetric system. In develop- ing a suitable replacement for the EM 2000, a secondary goal was to ensure that the wide-area, general survey ca- pabilities were not lost with the addi- tion of a higher frequency MBE. The search included multifrequency MBEs to support the high-resolu- tion, narrower swaths for inspection and lower resolution, greater swath options for surveys. The Kongsberg EM 2040 provides the best option to replace the EM 2000. Its specs are as follows: 200/300/400 kilohertz wideband, 140° swath, 400 beams at 400 kilohertz, 0.7° by 0.7° beam pattern at 400 kilohertz and water column data. At 400 kilohertz with 400 beams, the EM 2040 provides excellent data from the shallowest depths, where camera inspection is near impossible to the maximum depth of the AUV. Water column data with the geochemical suite will support leak detection and identifcation. At the same time that research was being conducted on a suitable replace- ment for the MBE, investigation into much higher frequency proflers and laser measuring systems was conduct- ed to augment the MBE and camera data. It was decided to contract with a laser measuring company specializing in underwater laser systems to special- ly build a system for C&C that will ul- timately support the highest resolution bathymetric system on an AUV. The system specifcs are as follows: 1,400 beams per swath, 5-millimeter range resolution at an 8-meter altitude, 50° swath, 5-millimeter laser footprint and 29-point swath per second. Field Testing of an Inspection Class AUV In the fourth quarter of 2013, the C- Surveyor VI was successfully deployed in the Gulf of Mexico for full integra- tion testing of its newest capabilities. These tests included revisiting sites of wrecks previously surveyed with the AUV's older survey suite to compare the improvements in the resolution of (Top and Bottom) Laser data collected by C-Surveyor VI of pipeline with buck- le arrestors on the seafoor. AprilBook.indd 30 4/7/14 12:19 PM

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