Low-frequency ambient noise in the deep sound channel: the missing component

Abstract

There is an important component of the undersea ambient noise which has generally been overlooked or ignored. It is the noise which arrives at a sensor, located in a deep sound channel, by way of ducted sound propagation. It is generated at the surface and becomes channeled as a result of a gradually sloping sound channel axis and through repeated reflections from a sloping bottom. It can be of sufficient level to dominate the local measurement. Examples are given in which neglecting it leads to incorrect interpretation of results and erroneous conclusions, including agreement between modelling and measurement.