Extension of the long-line hydrophone calibrator to higher frequency

Abstract

The usable frequency range of the long-line hydrophone calibrator (LLHC) has been increased for endfire fields in a portion of the calibrator. The LLHC is a water-filled chamber for performing acoustic calibration of towed or other line arrays under operational environmental conditions. Projectors distributed along its length can produce an acoustic field equivalent to that seen by the array in open water from a sound source at any desired bearing and range. The original LLHC configuration was capable of measuring the sensitivity and directivity patterns of line arrays or modules up to 49 m long at temperatures from 2<th>°C to 35<th>°C, pressures up to 6.9 MPa, and frequencies from 5 Hz to 700 Hz. The LLHC has recently been modified in several ways to increase the usable frequency range to 2000 Hz for endfire fields over a 5 m long region inside the chamber. The modifications include changes to the way projector drives are computed, installation of thin-walled collars to make the acoustic impedance (and propagation speed) down the chamber more uniform, and the addition of four nonuniformly-spaced hydrophones. Results are presented that show maps of the sound field uniformity inside the calibration chamber. [Work supported by ONR Code 321.]