An Acoustic Doppler and Electromagnetic Velocity Profiler

Abstract

A freely failing current meter called the Absolute Velocity Profiler (AVP) is described. This profiler is an expansion of a previously developed instrument, the Electro-Magnetic Velocity Profiler (EMVP), with the additional capability of acoustic Doppler (AD) measurements to determine the reference velocity for the EM profiles. The AVP measures the motional electric currents in the sea and the Doppler frequency shin of bottom-scattered echoes. The EM measurements yield a profile of the horizontal components of velocity relative to a depth-independent reference velocity; the AD measurements determine the absolute velocity of the AVP with respect to the seafloor. The EM profile is obtained from the sea surface to the bottom, and the AD measurements are obtained within about 60?300 m of the seafloor. The combination of the EM and AD measurements yields an absolute velocity profile throughout the water column. Performance analyses show the method is accurate to within 1?2 cm s?1 rms. The profiler also measures temperature and its gradient.