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MARIN decided to tackle the problems associated with measuring underwater motions by developing a new Underwater Motion Measurement System. For years, MARIN has been able to measure 6 Degree of Freedom (DoF) motions for floating structures using Krypton (now Nikon), Rodymm DMM optical measure- ment systems. This system uses three cameras mounted on a beam which track synchronised active markers on the model. These systems can measure motions of structures with the active markers above the water surface. Traditionally, motions of submerged structures were determined using accelerometers or video recordings. Determining low-frequency motions from accelerometers is very inaccurate. Using video recordings to determine the motions is very time-consuming and this technique can only be used to determine motions in the camera plane. Due to an increasing number of projects contain- ing subsea structures, such as disconnectable turret moor- ing systems and mid-water riser support arches, and the industry’s questions about their underwater behaviour, in 18 MTR September 2010 Design Underwater Motion Measurement System by Reinier Bergevoet, MARIN UMS camera and ultra bright red LEDs
