What is the difference between MBES and SSS in marine environmental surveys?

MBES (multibeam echosounder) creates detailed 3D seafloor maps using multiple sonar beams, while SSS (side-scan sonar) produces acoustic images of the seabed using side-facing sound pulses. MBES excels at bathymetric mapping and precise depth measurements, whereas SSS specialises in detecting objects and textures on the seafloor. Both technologies serve different purposes in marine environmental impact assessment projects.

Selecting the right underwater survey technology significantly affects your project’s success and data quality. Explore our comprehensive marine survey solutions to understand how these technologies can support your environmental assessment needs.

What exactly are MBES and SSS technologies in marine surveys?

MBES (multibeam echosounder) uses multiple sonar beams arranged in a fan-shaped pattern to measure water depth and create detailed bathymetric maps. SSS (side-scan sonar) transmits acoustic pulses sideways from a towfish or a hull-mounted transducer to create acoustic images of the seafloor and detect objects.

The fundamental difference lies in their data collection approach and output. MBES focuses on precise depth measurements across a wide swath beneath the survey vessel, producing accurate 3D representations of seafloor topography. This technology operates by transmitting sound pulses downward and measuring the time it takes for echoes to return from different points on the seabed.

SSS, conversely, creates acoustic shadows and reflections that reveal seafloor textures, sediment types, and artificial objects. The technology works by transmitting sound pulses perpendicular to the survey vessel’s track, creating detailed acoustic images that resemble underwater photographs. These images help identify changes in bottom composition, locate debris, and detect archaeological features.

Both technologies use sound waves but serve distinct purposes in marine environmental surveys. MBES provides quantitative depth data essential for navigation safety and volume calculations, while SSS delivers qualitative imagery crucial for habitat mapping and environmental monitoring.

How do MBES and SSS differ in data collection methods?

MBES employs multiple narrow beams (typically 200–400 beams) arranged perpendicular to the vessel’s direction of travel, measuring depths across a swath width of 3–5 times the water depth. SSS uses two wide-angle acoustic beams transmitted horizontally, covering areas up to several hundred metres on each side of the survey track.

The frequency ranges differ significantly between these technologies. MBES typically operates at higher frequencies (200–400 kHz) for shallow-water surveys, providing excellent resolution but limited range. Deeper-water systems use lower frequencies (12–100 kHz) to achieve greater penetration. SSS commonly operates at frequencies between 100 and 500 kHz, with higher frequencies offering better resolution for detailed object detection.

Data acquisition processes also vary considerably. MBES requires precise vessel positioning and motion-compensation systems to ensure accurate depth measurements. The technology demands real-time processing of multiple beam angles and travel times to create georeferenced bathymetric data.

SSS data collection focuses on acoustic backscatter intensity rather than precise positioning. The system records the strength of returned acoustic signals, creating greyscale images in which hard surfaces appear bright and soft sediments appear dark. This approach reveals seafloor characteristics that depth measurements alone cannot capture.

Which technology provides better results for environmental impact assessments?

The choice depends on specific assessment objectives. MBES excels in habitat volume calculations, sediment transport studies, and precise change detection, while SSS performs better for benthic habitat classification, debris surveys, and archaeological investigations within marine environmental impact assessment frameworks.

MBES offers superior accuracy for quantitative analysis, with vertical precision typically within 0.2–0.5% of water depth. This precision makes it ideal for monitoring coastal erosion, tracking sediment movement, and calculating dredging volumes. The technology’s ability to detect subtle bathymetric changes supports long-term environmental monitoring programmes.

SSS provides broader area coverage and better object-detection capabilities. A single survey line can map corridors several hundred metres wide, making it efficient for large-scale habitat surveys. The technology excels at identifying artificial reefs, shipwrecks, cables, and pipelines that may affect marine ecosystems.

Environmental impact assessments often benefit from combining both technologies. MBES provides the quantitative foundation for impact calculations, while SSS reveals ecological features and potential environmental sensitivities that numerical data might miss.

What factors should you consider when choosing between MBES and SSS?

Survey objectives should drive technology selection. Choose MBES for projects requiring precise depth measurements, volume calculations, or bathymetric change detection. Select SSS for habitat mapping, object-location surveys, or when broad area coverage takes priority over depth accuracy.

Budget considerations significantly influence technology choice. MBES systems typically require higher initial investment and operational costs due to complex positioning requirements and data processing needs. SSS offers more cost-effective area coverage, making it suitable for preliminary surveys or projects with limited budgets.

Timeline requirements also affect selection. SSS surveys generally progress faster due to wider coverage patterns, potentially completing large areas in shorter timeframes. MBES surveys require slower, more methodical approaches but deliver comprehensive depth data that may eliminate the need for additional surveys.

Environmental conditions affect both technologies differently. MBES performance degrades in very shallow water or in areas with complex topography, while SSS remains effective across various depth ranges. Water clarity affects neither technology, since both rely on acoustic rather than optical methods.

Consider your data output requirements carefully. Projects needing detailed 3D models, navigation charts, or engineering drawings benefit from MBES data. Investigations focusing on seafloor characteristics, environmental monitoring, or archaeological surveys often find SSS imagery more valuable.

Professional expertise availability influences practical implementation. MBES requires specialists familiar with complex calibration procedures and data processing workflows. SSS operation and interpretation, while still requiring training, generally involves less technical complexity.

Making the right technology choice ensures your marine environmental impact assessment delivers the precise data needed for informed decision-making. Contact our marine survey specialists to discuss which approach best suits your specific project requirements and environmental assessment objectives.

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