Abstract:
To obtain high-resolution measurements of acoustic spatial variability in shallow water (SW) and very shallow water (VSW) over a wide range of environmental conditions, the Naval Research Laboratory has developed a highly stable multimode underwater vehicle that can be towed and its depth and attitude controlled via commands from the towing vessel. The vehicle was configured with manual and semiautonomous control systems, data acquisition and communications systems, and an acoustic sensor system for measuring acoustic variability in water depths from 20 to 100 ft. Two high-frequency (20- to 600-kHz) arrays were mounted flush on the sides of the tow body and operated in either broad-beam mode or ``phased-beam'' mode using the latest ``Doily'' technology developed at ARL Penn State. In ``phased-beam'' mode the arrays form sine and cosine shape functions, with the beam steer angle dependent on frequency of operation. Through selection of tow speed and pulse repetition rate, the scattering characteristics of the same area of ocean bottom are simultaneously measured over a wide range of frequencies. Technical details of vehicle design and operation and some results from a high-frequency experiment conducted during 1996 are presented.