On the use of active low-frequency sonar systems for the monitoring of littoral environment

Abstract

The aim of conventional low-frequency sonar systems is either to detect and classify targets (containers, fish schools, submarines, divers, mines,...) or to communicate between two or more underwater geographical locations (communication, tomography). The increase of both military and civilian interest in shallow-water areas (typically from the shelf break to the shore), requires a better understanding of the effects of oceanographic environment on acoustic propagation and reverberation. Unfortunately, the available environmental information concerning bottom characteristics, sound-speed variability (in databases or charts), is often inaccurate and unreliable and, most of the time, it does not cover very wide areas. Hence, in order to get a comprehensive environmental knowledge during operations and to improve performance prediction, low-frequency sonar systems are now equipped with environment assessment functionality. Experimental results concerning the impact of shallow-water environment on sonar signals will be presented. Two major aspects will be investigated: the impact of both sound-speed profile variability and bottom heterogeneity. The optimization of low-frequency sonar design and its use for the assessment and the monitoring of littoral environment (i.e., acoustic data inversion) will then be discussed.