Department of Physics
Associate Professor Chris Tindle
MSc, PhD (Brit Col), FNZIP, FASA
Wavefront modelling is a new method of calculating waveforms in underwater acoustics. It is based on ray tracing but uses a depth-time diagram which is found by tracing a fan of rays to the desired range and finding their depth and travel time. The depth-time diagram determines the arrival times and amplitudes of pulses at the receiver. The phase of the received pulses is found from the phase changes accumulating from reflection and refraction turning points. An integral for each ray arrival can be evaluated numerically or analytically with stationary phase methods and gives a full description of caustics, cusps and shadow zones even at low frequencies. The method is fast and able to handle very rapid range dependence such as occurs in shallow water with surface waves. The underside of a wave crest acts like a curved mirror and focusses sound to give large fluctuations in sound intensity as waves pass over.
Acoustics and Marine Larvae
Many fish and crustaceans have a larval stage which drifts in the open ocean. The larva must then find suitable reef habitat in which to settle. The larva of many species actively swim towards reefs and it is thought that some of them use the underwater sound field to find their way. Experiments to determine the underwater "soundscape" and the navigational cues used by marine larvae are in progress.