Development and Testing of an Engineering Prototype for a Marine Version of the Berkeley Unexploded Ordnance Discriminator (BUD)

Abstract : A marine version of the Berkeley Unexploded Ordnance Discriminator [BUD] has been built and tested in shallow seawater. The system was built in response to a need to develop a geophysical system for detecting and characterizing UXO in the marine environment. Such a system must detect a metallic object, provide its depth and symmetry properties that allow it to be identified as an intact UXO. A three-component transmitter is mounted on a planar base and four three-component receivers are mounted on the same base and on the corners of a square pattern centered on the transmitter. Differences in field at symmetrically located receivers cancel the response of the seawater and of the air-sea interface above the system. New ferrite-cored induction coils coupled with a feedback amplifier scheme provide high stability and a critically damped response. The coils are mounted in rigid blocks to provide three-component sensor modules. A first stage of amplification at the sensors provides a high level signal from a low impedance source to carry the signals, without added coupling noise, over cables to differencing amplifiers in the data acquisition module. The current pulse in the transmitter coils is a bipolar half-sine of 5 msec. duration with a repetition rate of 12.5 Hz. A new pulser, based on the BUD pulser provides a peak moment of 2000 Amp. Turns M2 with current pulses of 200 A and a net power consumption of 400 Watts. Tests of the prototype on land and in 5 m of seawater showed that the system clearly detected a 6 inch \201152.4 mm\202 steel test ball to over 57 cm depth and that the test ball yielded identical transients in air and seawater showing that the effects of the seawater and the air-sea interface were canceled in the new configuration.