Mobile Acoustic Source for Underwater Acoustic Measurements

A small, low cost, expendable UUV, equipped with a broadband acoustic source, has been developed for in-situ transmission loss (TL) and other acoustic measurements. The mobile acoustic source vehicle, developed by OASIS (OMAS), is 12.4 cm in diameter, 91.4 cm long and weighs 10 kg. OMAS can be programmed to follow different run geometries by varying course, depth, and speed while transmitting various acoustic waveforms. Unique to the system is the ability to time synchronize the source with the hydrophone receivers, thereby enabling the calculation of source range from the measured time delay between signal transmission and reception. In a recent application, both hyperbolic frequency modulated (HFM) slides and orthogonal continuous wave (CW) signals were transmitted. In real time and on a ping-by-ping basis (once per minute), the received HFM signals were matched-filter processed such that the source range and TL were measured, along with bearing (with use of a horizontal array). The paper will describe the overall capabilities and uses of the OMAS, including measured source level, directivity, waveform design and vehicle radiated noise level. Also, an example of TL data from recent shallow water experiments with the OMAS will be shown