An improved version of the Marine Berkeley Unexploded Ordnance Discriminator characterization system (MBUD), called MBUD2, has been built and tested. The improved version incorporates technical modifications to eliminate the noise encountered in seawater with the MBUD1 version and a new data acquisition system.
The object was illuminated with fields from three orthogonal transmitters, and the signal was measured using four three component receivers. The receivers were arranged in a configuration that inherently cancels the response of the system to enclosing seawater, and to the response of the air-sea interface for shallow deployments. The system was operated as a cued system. It was mounted on a simple platform on a top of a support structure that was transported to a predefined survey location by the carrier boat, lowered to the sea bottom, and maneuvered by the diver. The support structure extended one meter below the system platform to allow for the object placement to a specific location by the diver in low-visibility conditions. MBUD2 was able to classify a detected object on the basis of its size, orientation, depth, shape and metal content. It was done by estimating the principal dipole polarizabilities of a target using 33 channels of normalized induction responses computed at 46 logarithmically spaced times between 0.0005 and 0.013 s.
The results clearly show that MBUD2 can resolve the intrinsic polarizabilities of the target, and that there are very clear distinctions between symmetric intact UXO and irregular scrap metal. The system was tested on land and in San Francisco Bay with excellent results. The system performs according the design and specifications: it cancels the response of the seawater and airsea interface, measurements are stable and repeatable, and target responses estimated from marine measurements are identical to those from land measurements.
This project represents an important demonstration of the value of advanced electromagnetic induction (EMI) sensors in the underwater environment.