The Effect of Temperature Inhomogeneities in the Ocean on the Propagation of Sound

Abstract

Horizontal small-scale temperature inhomogeneities in the ocean have been measured with the aid of a highly sensitive, rapid-response thermometer mounted on a submarine. The mean size of these inhomogeneities is of the order of 60 cm; a typical average temperature variation is 0.05°C. The physical features of the inhomogeneities which determine acoustical effects are shown to be described by the autocorrelation function; a specially constructed computing machine was used to calculate this function from the temperature records. The calculated backward scattering (reverberation) resulting from these inhomogeneities is given as a function of frequency. In the region 10 to 100 kc the calculated scattering is, in general, less than that which is actually observed in the ocean, suggesting that biological material is the major source of scattering in the ocean. A calculation of the attenuation of transmitted sound in the ocean resulting from scattering shows that this effect is small compared with absorption at the higher frequencies. Refractive effects of the inhomogeneities result in another acoustical phenomenon: local warping of the wave fronts produces intensity enhancement or diminution at the receiver. These effects quantitatively explain rapid acoustic fluctuations (scintillations) which are observed in the ocean.