Side-Scan Sonar vs. Multibeam Sonar: A Comparison of Two Underwater Surveying Technologies

In underwater surveying, marine exploration, and fisheries monitoring, sonar technology plays a crucial role in capturing accurate data. Whether it’s for seabed mapping, underwater obstacle detection, or marine resource exploration, sonar provides the necessary insight to understand the underwater environment. Two of the most widely used sonar technologies are side-scan sonar and multibeam sonar. These systems differ significantly in their working principles, applications, and advantages. Understanding these differences is essential when choosing the right equipment for your project.

In this article, we will explore the differences between side-scan sonar and multibeam sonar, helping you understand the unique features of each system, their advantages, and their ideal applications.

1. Basic Operating Principles

1.1 Side-Scan Sonar

Side-scan sonar is a system that uses sonar waves to create images of the seafloor and underwater objects. The sonar emits acoustic waves from transducers mounted on the sides of a vessel. These waves travel through the water, reflect off the seabed or underwater objects, and return to the sensor. By measuring the time it takes for the sound waves to return and their intensity, the system generates an image of the underwater surface.

• Scanning Method: Side-scan sonar emits acoustic waves in a fan-shaped or sideward pattern to scan the seafloor laterally.
• Imaging Output: It produces a 2D image, resembling a “strip map,” suitable for detecting underwater objects, structures, and seabed features.

1.2 Multibeam Sonar

Multibeam sonar emits multiple sonar beams simultaneously, covering a wider area in a fan-like or sector-shaped pattern. The sonar transducers emit beams at different angles, capturing data from several points at once. By processing these returns, the system generates detailed three-dimensional images of the seafloor and underwater features.

• Scanning Method: Multibeam sonar uses multiple beams to scan a broad swath of the seabed, providing simultaneous depth measurements at various angles.
• Imaging Output: It generates 3D maps of the seafloor, allowing for precise depth measurements and detailed topographical mapping.

2. Key Differences

2.1 Imaging Method and Data Output

• Side-Scan Sonar: Side-scan sonar primarily produces a 2D “strip map” of the seafloor. While it provides detailed imaging of underwater objects, wrecks, rocks, and other structures, it does not offer depth information. Thus, side-scan sonar is best suited for detecting and identifying objects on the seafloor or within the water column.
• Multibeam Sonar: Multibeam sonar provides 3D data, allowing for the generation of precise seafloor bathymetry. It captures detailed depth measurements across a large area, producing a comprehensive topographic map of the underwater landscape. This makes multibeam sonar ideal for large-scale seabed surveys and precise depth measurements.

2.2 Coverage Range

• Side-Scan Sonar: Side-scan sonar typically covers a wider area horizontally but has a relatively limited vertical range, often up to 4 to 6 times the water depth. It is great for broad scanning of underwater features but lacks the ability to provide accurate depth data.
• Multibeam Sonar: Multibeam sonar offers a broader and deeper coverage, often achieving a horizontal scan range of 10 to 12 times the water depth. It is not only capable of covering large areas but also provides precise depth information, making it ideal for large-scale seabed mapping and deep-sea exploration.

2.3 Cost and Complexity

• Side-Scan Sonar: Side-scan sonar equipment is relatively simpler, more lightweight, and less expensive. It is easier to operate and maintain, making it a popular choice for smaller-scale surveys or quick object detection tasks. The lower cost makes it accessible for a variety of industries, including fisheries and environmental monitoring.
• Multibeam Sonar: Multibeam sonar systems are more complex and come with a higher price tag. They require advanced data processing capabilities, multiple sensors, and a more skilled operator. However, the increased investment is justified by the system’s ability to provide high-resolution, 3D seafloor mapping and accurate depth data, which is essential for large-scale marine surveying and deep-water exploration.

2.4 Ideal Applications

• Side-Scan Sonar: Side-scan sonar is ideal for underwater object detection, seabed mapping, wreck location, fisheries resource assessment, and search and recovery operations. Its ability to generate high-resolution images of specific areas makes it perfect for detecting submerged objects, marine debris, and underwater obstacles.
• Multibeam Sonar: Multibeam sonar is suited for seabed mapping, bathymetric surveys, geological studies, and deep-sea exploration. It provides comprehensive data on seafloor topography, which is essential for underwater construction projects, environmental monitoring, and offshore engineering.

3. Summary

While both side-scan sonar and multibeam sonar are powerful tools for underwater surveying, they differ significantly in terms of data output, coverage, and application. The key differences between the two systems are summarized as follows:

• Side-Scan Sonar:
  • Produces 2D imagery of the seafloor.
  • Best for object detection, obstacle mapping, and water column imaging.
  • Limited vertical coverage (4–6 times the water depth).
  • Lower cost, simpler operation, and maintenance.
  • Ideal for small-scale surveys and quick object detection.
• Multibeam Sonar:
  • Generates 3D topographic maps of the seafloor with precise depth data.
  • Best for large-scale seabed mapping, bathymetric surveys, and geological exploration.
  • Greater vertical and horizontal coverage (10–12 times the water depth).
  • Higher cost, more complex operation, and requires skilled personnel.
  • Ideal for detailed marine surveys and deep-sea exploration.

Choosing between side-scan sonar and multibeam sonar depends on the specific needs of your project. For smaller-scale tasks such as object detection or localized surveys, side-scan sonar may be the better option due to its lower cost and simplicity. However, for large-scale surveys, deep-sea exploration, or tasks requiring precise depth measurements, multibeam sonar is the clear choice due to its comprehensive 3D mapping capabilities.

In many cases, the two technologies can complement each other, providing a full suite of sonar data that meets the diverse needs of modern underwater exploration.