Physical Oceanography, Vol. 13, No. 5, 2003
EXPERIMENTAL AND FIELD RESEARCH
SPECIFIC FEATURES OF THE INFLUENCE OF THE LOWER BOUNDARY OF A
WAVEGUIDE ON THE ANGULAR STRUCTURE OF THE SOUND FIELD IN THE
SHELF ZONES IN THE NORTHWEST PART OF THE BLACK SEA
V. K. Bogushevich, L. N. Zamarenova, and M. I. Skipa
We analyze the possibility of existence of critical angles of incidence of sound waves along two
paths of propagation of sound typical of the northwest shelf of the Black Sea from the viewpoint
of the characteristics of the lower boundary of a waveguide and the space and time structure of
the field of sound velocity. The lower boundary of the waveguide may possess the property of
acoustic transparency both in the case of a subsurface sound channel and under the conditions of
negative refraction if the bottom is formed by fine-aleurite silts responsible for significant losses
in the process of propagation of sound. The angles of total internal reflection exist for bottoms
formed by shell rocks under all hydrological conditions typical of this region. At the same time,
for bottoms formed by fine-aleurite silts, these angles exist only for a certain vertical structure of
the field of sound velocity, which enables one to use the range of angles in which the losses
caused by the reflections of sound waves from the bottom can be neglected.
To solve practical problems encountered in the process of monitoring of coastal waters, it is necessary to
guarantee the maximum possible distance of propagation of sound in the shelf zone.
The range of action of hydroacoustic devices in shallow-water regions of the World Ocean is seriously lim-
ited . Thus, in particular, under the conditions of the northwest shelf of the Black Sea, it is, as a rule, equal to
several tens of kilometers but sometimes can be less than
. As one of the causes of significant losses
in the process of propagation of sound in these regions, one can mention specific features of the lower boundary
of a waveguide and the vertical structure of the field of sound velocity in the water layer.
We analyze the parameters of the lower boundary of the waveguide and water media as well as some fea-
tures of the angular structure of sound fields from the viewpoint of ray acoustics in the process of propagation of
sound whose frequency is higher than
along two paths one of which is directed from the northernmost
point of the Tendr Island toward the Bol’shoi Fontan Cape and the other is directed southward. These two paths
are characterized by bottom sediments and the vertical structure of the field of sound velocity in marine media
typical of the northwest shelf zone.
First, we consider the characteristics of the lower boundary of the waveguide. As follows from the analysis
of the space structure of sediments and their properties, a single-layer model can be used as a geoacoustic model
of the bottom in the northwest shelf zone within the investigated frequency band. For the path connecting the
northernmost point of the Tendr Island with the Bol’shoi Fontan Cape, the geoacoustic model of the bottom is
constructed as a layer of fine-aleurite silts with the velocity of longitudinal waves c
sec and density
. For the second path directed to the south from the northernmost point of the
Tendr Island, the geoacoustic model of the bottom represents a layer of shell rocks with the velocity of longitudi-
nal waves c
sec and density ρ
Division of Hydroacoustics of the Marine Hydrophysical Institute, Ukrainian Academy of Sciences, Odessa. Translated from Morskoi
Gidrofizicheskii Zhurnal, No.
40–46, September–October, 2003. Original article submitted March 5, 2002.
0928-5105/03/1305–0279 $25.00 © 2003 Plenum Publishing Corporation 279