ASA 124th Meeting New Orleans 1992 October

1pEA8. Environmentally controlled free-field towed array calibration system.

M. K. Beason

L. D. Luker

M. J. Deebel

Naval Res. Lab., Underwater Sound Reference Detachment, P.O. Box 568337, Orlando, FL 32856-8337

The methodology, design, and capabilities of the long-line hydrophone calibrator (LLHC) are described. Towed-array calibrations normally require a large body of water to insure that the reflections from the sides, surface, and bottom have a negligible effect on the measurement. Additionally, it is difficult to measure directivity patterns on entire array modules. The LLHC will provide an environmentally controlled alternative to open water calibrations as well as the ability to measure directivity patterns and the complex free-field sensitivity of long underwater arrays. Extended projectors inside a closed tube are driven to produce an acoustic pressure field that is equivalent to a free-field plane acoustic wave propagating from any desired angle of incidence. Projector drives are determined by measuring the transfer function between the projectors and monitor hydrophones within the tube. The LLHC will provide complex free-field sensitivities and directivity patterns from 5 to 700 Hz at temperatures from 2 to 35 (degrees)C to depths over 650 m. Transducer configuration and mechanical issues will be discussed. Results from a recent prototype demonstration will be presented. [Work supported by NAVSEA.]