Sound Scattering Problems in the Ocean

Observations of sound scattering in the open ocean have shown not only the wide spread occurrence of stratified scatterers there but also have indicated ways in which acoustical methods can be employed to describe the distribution of life in the open ocean. One method employs the broad-band spectrum of an explosion fired at shallow depth as a sound source. The scattered sound is also received at shallow depth. The resulting data can be interpreted as variation in scattering cross section as a function of depth on the assumption of uniform horizontal layering of the scatterers. Detailed spectrum analysis shows that scatterers having different scattering spectra are found at different depths, and that they behave differently in their vertical migration. The identification of characteristic spectra with animal types has been advanced by observing that the spectrum of some layers is modified during their vertical migration in a way that suggests that the scatterers are fishes with swim bladders. Moreover, it is indicated that these spectrum changes will be useful in studying the function of swim bladders in fishes. Another approach to the problem of identifying deep sea sound scatterers is to combine sound scattering observations and photography. This technique has been used only a short time, but it has produced a number of pictures from which the scatterer could be positively identified.