A shadowgraph method for ocean acoustics

A knowledge of convection activity in the upper few hundred metres of the o cean is important in establishing ocean-atmosphere heat fluxes and in under standing large-scale water-circulation processes. The usual methods for inv estigating internal structures in the ocean have certain drawbacks. Lowerin g probes into the ocean can provide local information only, while towed arr ays of sensors are cumbersome and expensive. An alternative acoustic method for revealing internal structures is proposed. It is based on the observed acoustic intensity only and does not rely on phase or travel times. For th is reason it is really an acoustic shadowgraph. The method is explained and its successful use in a sea trial is reported.