Acoustic Doppler velocimeter evaluation in stratified towing tank

The performance of an acoustic Doppler velocimeter (ADV) was evaluated usin g a towing tank. Rudimentary tests of the speed response were followed by t ests of yaw and pitch response. Because only a few published land inconsist ent values of sound speed as a function of saltwater concentration were fou nd, a simple scheme was devised using the boundary-detection feature of the ADV to obtain such values. Tests were also run in the stratified tank to v erify the usability of the ADV there. The accuracy of the probe to horizont al flow fields is generally within the range of +/-0.25% +/-0.25 cm/s, and the yaw response is very nearly sinusoidal. Limited pitch-response tests su ggested an indicated overspeed of some 5-10% for horizontal velocities and an indicated underspeed of 5-15% for vertical velocities. A correction sche me was developed to allow the ADV to be used in high-concentration saltwate r, and its suitability was verified in homogeneous saltwater solutions. Whe n the same scheme was used in a strongly stratified tank, however, a small overcorrection was indicated. Tests on a new probe design suggested much im proved pitch response.