Side-Scan Sonar

What is Side Scan Sonar

Side-scan sonar (also sometimes called side imaging sonar, bottom classification sonar or SISS) is a sonar system used to create images of large areas of the ocean floor.

Side-scan sonar is most commonly used to highlight the differences in material and texture of the seafloor and scan for debris that may be dangerous to ships or pipelines.

How it works

A side-scan sonar uses high-frequency sound pulses bounced off the seafloor to create an image and show differences in seabed texture and illuminate foreign bodies. A side-scan sonar consists of two devices (transducers) that convert variations in pressure or brightness into an electrical signal. These transducers follow our scanning boat mounted in a towed body or ‘fish.’

Each transducer generates a fan-shaped sound pulse. When the sound pulse hits the seafloor, some of the sounds are reflected back to the transducer, and some are reflected away. The returned sound is known as backscatter.

Strong return (high backscatter) typically occurs when the sound is reflected off hard and rocky surfaces, while weak return (low backscatter) occurs if reflected off softer sediments (e.g. sand).

Because of the geometry of the sound pulse sent toward the seafloor, an obstacle rising above the seabed, such as a shipwreck or steep hill, can cast shadows in the sonar image. The size of the shadow can be used to determine the size and shape of the feature.

Over time, as the sonar moves along, the recorded sound reflections form an acoustic image of the seafloor. Typical frequencies used in side scan sonar range from 100 to 500 kHz, with higher frequencies producing a higher resolution image.