The ability to determine the size distribution of a field of bubbles has a wide range of practical applications. Bubbles have traditionally been detected by using either optical or acoustic techniques. Bubbles exhibit strong acoustic resonance properties dependent on their size. By probing a field of bubbles it is possible to form an estimate of the range of sizes present by analysing the scattered data. There are a number of acoustic bubble sizing methods currently available, some of which exploit the nonlinear dynamic behaviour of the bubble. By modeling this behaviour, improvements may be made to the estimation techniques. This paper presents estimates for the quadratic transfer function of a single bubble based on the Volterra series. A method of estimating the Volterra kernels using a neural network is presented which significantly reduces the quantity of data required to form an estimate of the transfer function.

This paper presents the development and performance of blind algorithms for a spatial diversity scheme to enable reliable data telemetry over a long range underwater acoustic channel. A number of Bussgang based stochastic gradient algorithms were tested for this multipath channel with additive white and coloured shipping noise. Both simulation and real experimental tests have shown that a significant improvement is obtained by utilising the spatial diversity of the long range channel and the ability of the combiner to perform joint equalisation and carrier phase tracking.

This paper describes a parallel architecture that has been developed to perform real-time synthetic aperture sonar imaging as part of the Acoustical Imaging Development (ACID) project. The project has successfully developed a synthetic aperture sonar system for producing high resolution images of the sea floor and that has been tested during a series of sea trials in May 1993 off the south coast of France. This paper describes the synthetic aperture processing system developed by the University of Newcastle upon Tyne and its use of transputer modules and associated devices in order to obtain real-time imaging performance, the software structure of the processing system and the load balancing techniques that have been developed in order to provide efficient processing. The use of a parallel distributed architecture has also allowed a processing system that can readily be extended to deliver greater computational power in the future. Images produced by the synthetic aperture processor from data collected from around the Toulon coastal region are presented. These images highlight the improvement in azimuth resolution that can be obtained from synthetic aperture processing over conventional sidescan sonars.