Separation of acoustic normal modes in shallow water

Abstract

The normal mode method is widely used for the acoustic field presentation in the deep ocean. In shallow water, the advantages of the mode description are not obvious, since in this case the mode structure is determined by the boundary conditions at the bottom and the surface, the properties of which are most often unknown, and are also nonstationary in space and time. Under such conditions, it is not clear to what extent the mode representation obtained in numerical models corresponds to reality. The authors studied the mode structure of several shallow water bodies and the coastal shelf of the White Sea. In the case when it was possible to measure the vertical profile of the field at the receiving point, the mode profiles are easily distinguished and can be used, for example, to determine unknown boundary conditions at the bottom and surface, including in the presence of ice cover. A method has been developed for identifying modes in the case of field reception by single spaced hydrophones; the difficulty in this case is that at each moment of time the received signal contains all propagating modes that have to be selected in subsequent processing.