Side-Scan Sonar as a Tool for Seafloor Imagery: Examples from the Mediterranean Continental Margin

Abstract

The majority of the ocean world’s features are being discovered, identified, characterized and imaged by their interactions with sound (Medwin and Blue, 2005). Often a specifically designed sound source is used to learn about the sea and its boundaries (Medwin and Clay, 1998), as in the case of the use of acoustical geophysical devices that provide information about the seafloor and the strata below, transforming the things that we cannot see into numerical data and pictures which give us a model that is able to visually represent the seabed and to outline its physical proprieties and processes (Morang et al., 1997). Such a model, based on the behaviour of the sound pulses and their interaction with water, sediment, rocks and the whole marine environment in which they are emitted, reveals diverse seascapes from shallow water to deep sea and allows us to determine the nature and characteristics of the seabed and additionally, to promote a wide range of practical applications. The research in the marine environment (from oceanography to marine geology, benthic ecology, marine archaeology etc.) now depend heavily on such tools, that provide, as the first step in obtaining the information, the geological framework that can further promote focussed scientific investigations and also better drive seabed utilization for social and economical purposes. The indirect techniques of investigation used for exploration and study of the submerged environment are different and change according to particular research purposes (Jones, 1999). Generally, acoustical geophysical devices are sound sources that work by transmitting and receiving the sound waves that are reflected, diffracted or scattered off the bottom. They differentiate themselves from each other by the different frequencies employed and thereby the different information that are able to provide about the seabed’s proprieties (table 1, Morang et al., 1997). Echo-sounders, side-scan sonar and sub-bottom profilers are the three principal acoustic devices, used to map the seabed in sea exploration programmes, collecting geophysical data that in turn produce morphological and sedimentary models which became instrumental in determining and understanding the geomorphology and the present-day (Holocene) sedimentary processes of the investigated areas. Echo-sounders with a single-beam (Single-Beam Echo-Sounder – SBES) are used for hydrographic (bathymetric) surveys. The Multi-Beam Echo-Sounders (MBES) represent an