Acoustic Characteristics of Deep Scattering Layers as Related to Oceanographic Provinces

Abstract

The characteristics of sound backscattered from layers of biological origin in the deep ocean have been the subject of several investigations. These characteristics give information on the densities and sizes of scatterers and their distribution with depth. The parameter most often measured is the scattering strength as a function of frequency, time of day, and location. Near-surface fired explosives were used as sound sources and hydrophones as omnidirectional and directional wideband receivers. The directional unit, an inverted cone reflector containing a line hydrophone, permits a constant, narrow beamwidth over three octaves; thus it is superior to the conventional single frequency echo-sounder for detecting the resonant scatterers of biological origin which are the main contributors to reverberation from the ocean volume. Measurements made in the North and South Atlantic and in the Pacific over a wide variety of oceanographic conditions indicate that major changes in scattering behaviour occur near oceanographic boundaries.