Side Scan Sonar Equipment

Side scan sonars (SSS) are the underwater sound instruments used in hydrographic surveys, harbor security, marine search and salvage, mine counter measures (MCM), scientific ocean floor mapping, etc. Energy levels and operating frequencies of side scan sonars are usually far above the hearing ability of marine mammals.

Typical side scan sonars contain power supply, top side computer with digital storage, controlling, decoding and visualizing software, telemetry and data communication link to wet-side electronics through a long, reinforced electrical or fiber-optic cable, towed pressure vessel with stabilizing swimming gear (tow fish), two active acoustic arrays, as well as few positioning sensors (pitch/roll, bearing, GPS, pressure).

Acoustic arrays alongside the tow fish platform transmit narrow, fan-like beams that hit the sea floor at 20-30° grazing angles on each side across the vessel path. Over the time they produce short bursts of acoustic energy (chirps, pulses), typically repeated every 1 to 10 times per second. That allows to virtually slice up water space below into narrow vertical slices as the tow fish advances at speeds of 4-5 knots.

Amplitudes of the received and processed echoes from within the sequential slices are brought up to the computer screen and plotted side by side in a waterfall fashion in real time to highlight and visualize the contours of the bottom objects, with their shadows, and any natural artifacts that fall into the sonar range.

To make it more efficient, each side scan array can operate in two different frequency modes, low (L) and high (H), and feature construction in order to reduce inter-modal coupling, increase bandwidth and enhance sonar sensitivity.

Most side scan sonars emit sound waves of 100 kHz to 2 MHz, have swath ranges of 50 meters to over 2 km, and range resolution of few 1 mm to 1 meter. Side scan sonars and arrays that are mountable on autonomous underwater platforms (AUV) tend to have higher frequencies and higher angular resolution as a trade-off to light weight and shorter sonar ranges.