Side-Scan Sonar

Side-scan sonar creates detailed pictures of the seafloor by utilising sound energy and analysing signal returns. This enables rapid and cost-effective mapping of large seabed areas, detecting objects and identifying bathymetric features regardless of water clarity.

Side-scan sonar operates by emitting fan-shaped acoustic pulses down toward the seafloor across a wide angle perpendicular to the path of the sensor. These conical or fan-shaped pulses typically create a wide beam in the vertical plane (40-60°) and a narrow beam in the horizontal plane (0.2-4°). The sound frequencies used vary based on survey objectives—lower frequencies (50-100 kHz) cover larger areas at lower resolution, while higher frequencies (500 kHz to 1 megahertz) record smaller areas with greater detail. When these acoustic pulses encounter the seabed, they reflect back with varying intensities depending on the material properties. Hard surfaces like rock outcrops reflect more sound and produce stronger return signals than softer areas such as sand or mud, creating distinctive patterns of light and dark areas in the resulting imagery.

A complete side scan sonar system consists of several key components working simultaneously. The primary element is the towfish—a streamlined underwater housing containing the transducer arrays that emit and receive acoustic signals. These transducers convert electrical energy into sound waves and vice versa. The towfish can be towed behind a vessel using a cable system or mounted directly to a vessel's hull. Other essential components include a central processing unit (CPU) for data acquisition, handling systems (winch, tow cable, deck cable & usbl), and positioning equipment. Combined side scan sonar systems often integrate additional capabilities, such as sub-bottom profiling or bathymetric mapping, enhancing survey efficiency by collecting multiple data types simultaneously. The EdgeTech 4125 & 4200 Dual Frequency systems represent a modern example of professional side-scan technology.

The side-scan data acquisition process begins with proper system configuration and calibration. As the vessel traverses the survey area, the towfish emits acoustic pulses while the system records the intensity and timing of signal returns. This data is transmitted in real-time to the topside computer via the tow cable. Using specialised software such as Chesapeake SonarWiz, operators can monitor data quality during acquisition and make adjustments as needed. The SonarWiz workflow includes sonar interface setup, navigation input configuration, and output device setup. Post-acquisition, the scan sonar imagery undergoes processing to create geo-referenced mosaic TIF images. Fully integrated with the vessel's navigation system, positional coordinates are automatically captured with the side-scan data, enabling accurate spatial referencing. This comprehensive workflow provides users with detailed seafloor mapping capabilities essential for applications ranging from archaeological surveys to infrastructure inspection.

Side-scan sonar is an acoustic imaging system that maps the seafloor by emitting fan-shaped sound pulses perpendicular to its travel path. It detects objects through signal strength analysis and creates high-resolution imagery of large areas quickly, making it invaluable for navigation, archaeology, and environmental surveys in various underwater environments.

Side-scan sonar is optimal for efficient seafloor mapping and object detection applications. It excels in marine archaeology, shipwreck hunting, search and recovery operations, UXO detection, and environmental monitoring. It's particularly valuable when surveying hazards to shipping lanes, inspecting subsea installations like pipelines, and conducting geological mapping of the seabed.

Side-scan sonar systems operate at various depths depending on their configuration and frequency. While they don't measure depth themselves, they can be deployed in shallow coastal areas to deep ocean environments. The operational depth depends on the towfish altitude (typically maintained at 10-20% of the sonar range) and cable length, with deep-water systems requiring up to 5,000m of cable for effective deployment.

Side-scan sonar's primary limitations include its inability to provide bathymetric data (depth measurements), lower resolving power at greater distances, and the nadir gap directly beneath the towfish. The system requires continuous forward movement in predetermined patterns, limiting operational flexibility. Additionally, it can be sensitive to noise and multipath interference, potentially affecting data accuracy in complex environments.