The IEEE Seventh Working Conference on Current Measurement TechnologyCurrent and Wave Monitoring and Emerging TechnologiesMarch 13-15 | Bahia Hotel | San Diego, CA, USA |
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Technical Program Accomodations Order the Proceedings Committee and Contact Info |
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Deep ocean experience with acoustic current metersNelson Hogg and Dan FryeMS 21 Phone: 508.289.2791 As part of a program to develop a 5-year subsurface mooring capable of periodic telemetry ("Ultramoor") we have tested candidate current meters based on acoustic travel time (the Nobska MAVS and the FSI 3DACM) and Doppler (the Nortek Aquadopp and the Aanderaa RCM-11) principles. The advantages of these modern instruments over our longstanding workhorse, the VACM, are many, but the most important are that they have no moving parts and they have modern communications interfaces. However, in the first deployment of Ultramoor south of Bermuda we discovered consistent disagreements between the instruments with the RCM-11 registering lower speeds and the MAVS and 3DACM higher speeds than our reference VACM. Direction biases were also evident. The second Ultramoor deployment in Nov 2001 has confirmed these discrepancies and led us to deploy a third, short mooring offshore Bermuda expressly to compare the current meters. This mooring included a VMCM and an RCM-8, as well as 2 RCM-11s and a 3DACM, all positioned at about 4000 m depth in 4300 m of water. This comparison showed good agreement between the instruments, but left open the possibility that low scattering levels higher in the water column were causing the Doppler based instruments to underestimate the current. As a "final" test of this possibility we deployed 3 instruments
on a wire below a CTD configured to measure the (known) lowering rate
of the CTD as they were lowered from the surface to the bottom-passing
through relatively high and low scattering environments. The results and
implications from all these tests will be presented and discussed. Submitted on October 10, 2002 |
Sponsored by the Current Measurement Technology Committee (CMTC) of the IEEE Oceanic Engineering Society. All content reserved. Contact jrizoli@whoi.edu for more information. |
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