SideScan

Sidescan sonar is a sonar technique used to create images of the seafloor. Unlike bathymetric sonar that measures depth directly, sidescan maps the intensity of acoustic backscatter off the seabed. A transducer array emits fan-shaped beams to the left and right of a moving platform, typically a ship, towed behind a vessel, or mounted on an autonomous underwater vehicle or remotely operated vehicle. As the platform travels, the returning signal is recorded as a grayscale image, where brighter areas indicate stronger backscatter (often harder or more reflective materials) and darker areas indicate weaker backscatter (softer sediments or shadowed regions). Shadows behind elevated features help infer roughness and height.

Acquisition systems vary in configuration but share the principle of acquiring swaths on both sides of the track. The swath width depends on tow depth or altitude, frequency, and system design; typical surveys cover tens to hundreds of meters per side with higher frequencies yielding higher resolution but shorter range. Data are processed into georeferenced mosaics that can be used alone or in combination with bathymetric data.

Applications span underwater archaeology and shipwreck scouting, cable and pipeline surveys, habitat mapping, dredging support, and search-and-rescue operations. Interpretation of sidescan imagery requires consideration of factors that affect backscatter, including material type, surface roughness, moisture, and incidence angle, and is often complemented by other survey methods to provide accurate environmental context.