Side-scan sonar
Side-scan sonar produces acoustic images of the seabed. Towed by a survey vessel, it reveals objects, obstacles and changes in seabed texture.
CERES uses this imagery for seabed surveys, wreck searches and underwater target investigations. The sonar mosaic represents echo strength and acoustic shadows across the surveyed area.
Principle
The towed sonar, known as the towfish, transmits acoustic pulses to either side of the vessel’s track and records echoes from the seabed.
Travel time indicates the distance to a reflecting feature. Echo strength and acoustic shadows help reveal seabed texture, objects and obstacles. These images complement bathymetric measurements and other geophysical data.
Equipment
CERES operates EdgeTech side-scan sonar systems and a Kongsberg PulSAR 6100. The system, frequency and operating range are selected according to the survey area, target size and required image resolution.
EDGETECH 4200
Frequency: 300/600 kHz Range: 230/120 m Depth rating: 2,000 m Resolution: 0.03 m at 300 kHz and 0.015 m at 600 kHz Vertical beamwidth: 50°
EDGETECH 4125
Compact dual-frequency side-scan sonar
CHIRP acoustic imaging
Shallow-water surveys and target searches
Frequency and range depend on the selected configuration
KONGSBERG PULSAR 6100
Frequency: 500kHz-1MHz
range: 100m at 550 kHz
Depth range: 1000m
Resolution: 0.07m at 10m range, 0.35m at 50m range, 0.70m at 100m range
lobe opening: 50°
Methodology
Data Acquisition and Processing
Mapping
Survey lines, sonar range and towfish altitude are planned to provide the coverage and overlap required for a complete acoustic mosaic.
CERES defines these settings in the technical proposal, which may include a site plan showing the proposed survey lines.
Sonar acquisition and processing use Isis. Vessel positioning uses our own RTK system or the Orphéon network. Towfish positioning uses USBL acoustic positioning or a layback calculation, depending on the mission.
Survey speed is adapted to the required image quality, generally around 3 knots.
CERES supplies the georeferenced acoustic mosaic in GeoTIFF format, together with the raw and processed survey data in the agreed formats.
Sonar imagery can be combined with bathymetry and magnetometry to support seabed surveys, wreck searches and UXO investigations. Contact CERES to discuss your survey objectives.
