Abstract:

This presentation describes the results of the first calibration of line arrays in the long-line hydrophone calibrator (LLHC). The LLHC is a water-filled traveling-wave tube that simulates a plane-wave pressure field arriving from any bearing. It provides an alternative to open-water sensitivity calibrations and measures both sensitivity and directivity patterns over the array's operational environment. This is accomplished by measuring the electroacoustic transfer matrix between hydrophones and projectors that are placed within a steel pipe with an inner diameter of approximately 30 cm. This transfer matrix is then used to compute projector drives suitable for creating the desired sound field. The current LLHC configuration is capable of calibrating line arrays up to 48-m long at pressures from 0 to 6.9 MPa and frequencies from 5 to 700 Hz. The line arrays that were calibrated were approximately 43-m long containing up to 16 sensors. The calibrations were performed at pressures up to 2.7 MPa and frequencies ranging from 10 to 800 Hz. Measured directivity patterns for various frequencies will be presented and compared to predicted data. [Work supported by NAVSEA.]