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www.seadiscovery.com Marine Technology Reporter 19 2004 MARIN decided to develop a 6 DoF, contactless Underwater Motion Measurement System (UMS), com- parable to the above-water system. In close cooperation with the Krypton Corporation a modified version of its K600 optical measurement system was developed. K600 Adapted for Underwater Several changes had to be made to the original K600 system to be able to use it underwater. First, the infrared Light Emitting Diodes (LEDs) used for structures above water had to be replaced by different colour LEDs because the absorption of infrared light underwater is very large. After some research ultra bright red LEDs were chosen for the new UMS. Secondly, a watertight housing for the camera beam, including a stiff con- nection frame to the basin carriage, had to be manufactured. Using MARIN`s diffraction software, DIF- FRAC, the wave loads on the connec- tion frame and camera housing were determined and taken into account in the design. The frame has to be very stiff in order to minimise the motions of the camera beam because that has a big impact on measurement accuracy. Improved Measurement Quality Furthermore, a system of tracks was developed to be able to mount the camera on the basin floor, allowing camera positions below the object to be tracked. This track-mounting About the Author Reinier Bergevoet is project engineer at the Offshore department of MARIN.
