Precise heading and DGPS measurements of vessel motion improve VM-ADCP current measurements significantly

This paper describes how Vessel Mounted Acoustic Doppler Current Profiler (VM-ADCP) measurements are improved when accurate navigation data are available. Quality vessel velocity, position and attitude are required for determining absolute current measurements. While the ship´s position and attitude data are necessary to transform measurements made in the vessel fixed coordinate system into Earth fixed coordinates, vessel speed is required for correcting measured acoustic velocities. Experimental data presented in this paper result from a narrowband ADCP interfaced with the accurate integrated navigation system Seapath. Seapath integrates strapdown inertial motion sensor technology with satellite position measurement technology (GPS). Several comparison tests have been carried out to verify improved current measurements obtained with an ADCP-Seapath system