Hydroacoustic research capabilities in the large water tunnel at ARL Penn state

The Garfield Thomas Water Tunnel (GTWT) at the Applied Research Laboratory of The Pennsylvania State University is a 1.22m diameter test section, closed circuit water tunnel for hydrodynamic and hydroacoustic research. Acoustic measurements can be made with window or model flush mounted transducers, a focusing dish hydrophane mounted in a water tank above the test section, or with a 37 element array mounted downstream in the settling section. The acoustic sensors and environment of the largest water tunnel at ARL will be used to demonstrate the application and analysis of the passive sonar equation relative to making acoustic measurements in the controlled conditions of a water tunnel as well as for frequent background noise level analysis to ensure data validity. However, the paper will show that the magnitude of most individual elements cannot be accurately determined due to the boundary conditions of the tunnel. As a result, in-situ calibrations are relied upon to give a magnitude for combinations of the elements. Overall background levels for several sensors and tunnel conditions are presented as functions of velocity in terms of 'minimum measurable source level' for a test model which includes the transmission characteristics within the tunnel and the sensor's noise masking level. The current signal processing capabilities, in-situ calibration methodology, and proposed signal processing and background rejection improvements, including array improvements and acoustic nearfield holography, are all discussed.