Acoustic signals and data acquisition

Acoustics is the best and often the only means to investigate the water column and seabed efficiently and accurately. There is a large variety of instruments now available, and sonar mapping systems can be roughly divided into three categories: single-beam echo-sounders, multibeam echo-sounders, and sidescan sonars (

Figure 2.1

).

Figure 2.1.

The main sonar mapping systems are (from left to right) the single-beam echo-sounder, aiming straight below the surveying vessel and imaging a wide portion of seabed (and sub-seabed) at once; the multibeam echosounder, made of narrower beams and mapping a wide swath of seabed across the track of the surveying vessel; and the sidescan sonar, often towed separately and close to the seabed, imaging at grazing angles (adapted from the EC-ISACS project

http://www.ntnu.no/ISACS/

).