Acoustic Doppler Velocimeter Flow Measurement from an Autonomous Underwater Vehicle with Applications to Deep Ocean Convection

Abstract

The authors present a new modality for direct measurement of ocean flow, achieved by combining the resolution and precision of an acoustic Doppler velocimeter with the mobility of an autonomous underwater vehicle. To obtain useful measurements, two practical integration issues must first be resolved: the optimal location for mounting the velocimeter probe to the vehicle, and alignment of the velocimeter with the vehicle's attitude sensors. Next, it is shown how to extract earth-referenced flow velocities from the raw measurements. Vehicle hull's influence on flow velocity measurement is removed by modeling the vehicle as a spheroid in potential flow. This approach was verified by a tow tank experiment in the David Taylor Model Basin. The authors then describe mission configuration and signal processing for a deployment in the Labrador Sea to study deep ocean convection during the winter of 1998. Analysis of the vertical flow velocity data not only shows that this form of measurement can detect ocean convection, but also gives detailed information about convection's spatial structure.