A Method for Correcting Vertical Velocities Measured from a Vessel-Mounted Acoustic Doppler Current Profiler

Abstract

Minor alignment errors (?1°) can contaminate acoustic Doppler current profiler measurements of vertical velocities taken from a ship traveling at speed. The signature is consistently large positive or negative vertical velocities, recorded at all depths. A technique is proposed to postcorrect contaminated data in cases of tidally dominated flow over a flat bottom. The eigenmodes of the cross-correlation matrix of the depth-averaged velocities are found, and the data are rotated to align along the eigenvector corresponding to the smallest eigenvalue that is equivalent to the physical vertical direction. An example of corrupted data is presented, and corrections for the pitch and roll directions are found. The corrected flow field is shown to be physically plausible over both flat and sloping bottom sections of the cruise track.