The relative motion of the sediment grains as they roll over one another creates a characteristic acoustic signature. This sound signal provides the basis of an acoustic system for continuously monitoring the condition of the seabed in regions where mobility of the sediment is a concern. Sound transmissions in the ocean tend to be highly variable because the medium supporting the acoustic field is itself fluctuating. The fluctuations are associated with internal waves, turbulence, temperature variability, fronts and eddies. As well as stabilizing the final arrival, the time-reversal method offers the possibility of characterizing the fluctuations in the medium, which in turn should provide information on mixing processes and related phenomena in the ocean.
Acoustical oceanography is currently an area of intensive activity.
Novel techniques are constantly being developed in which sound is exploited to yield hitherto unattainable information on ocean processes. Many of the new methods are based on naturally generated sound in the ocean, created by both physical and biological sources. These sound signatures are providing information about the sources themselves and the medium through which they travel.