Side Scan Sonar vs Multibeam Echosounder represents one of the most fundamental technology choices in modern offshore surveying. Both systems use acoustic principles to image underwater environments, but they deliver fundamentally different data types, coverage patterns, and capabilities. Understanding the distinctions between multibeam versus side scan sonar is essential for selecting the right tool for bathymetric surveys, seabed mapping, object detection, and hazard identification. This guide explains the core differences, applications, and decision framework for choosing between multibeam sonar vs side scan technology.

What is a Multibeam Echosounder?

A multibeam echo sounder (MBES) is an active sonar system that transmits multiple acoustic beams simultaneously in a fan-shaped or sector pattern perpendicular to the vessel’s track. Each beam measures the vertical distance (depth) to the seafloor at a discrete angle. By combining data from dozens or hundreds of beams transmitted in rapid succession, multibeam systems generate high-resolution bathymetric maps showing precise seafloor elevation across a continuous swath typically 4-6 times the water depth wide.

Multibeam systems capture both depth (bathymetry) and intensity data (backscatter). Intensity information reveals sediment type and seafloor composition: soft mud returns weak reflections, while rock and gravel return strong, high-intensity signals. This dual data stream makes multibeam sonars versatile tools for comprehensive seabed characterization.

What is Side Scan Sonar?

Side scan sonar is a high-frequency imaging sonar that transmits narrow, fan-shaped acoustic beams to the sides (port and starboard) of the survey vessel. Sound energy reflects off the seafloor and submerged objects, and sensitive hydrophone receivers capture these reflections across a wide lateral distance from the vessel track. Travel time indicates distance to the reflecting object; signal amplitude indicates material hardness and texture.

Side scan sonar produces 2D grayscale imagery resembling aerial photographs of the seafloor. High-amplitude (bright) returns indicate hard materials or submerged objects; low-amplitude (dark) returns indicate soft sediments or shadow zones behind protruding features. Unlike multibeam, side scan does not measure water depth; it exclusively provides lateral imagery of seabed character.

Side Scan Sonar vs Multibeam Echosounder: Core Differences

1. Data Output and Imaging

Multibeam echo sounder vs side scan sonar differ fundamentally in their output:

Multibeam delivers 3D depth data organized in a georeferenced bathymetric grid. Every measurement has a precise X, Y, and Z coordinate. This enables generation of contour maps, digital elevation models, and volumetric calculations. Depth accuracy is typically ±0.5 to 1 meter (shallow water) and improves with system quality and water depth optimization.

Side scan sonar produces 2D grayscale imagery in a “strip map” format along the vessel track. Horizontal positioning is precise (georeferenced), but water depth is not measured. Target size and material property are inferred from reflection intensity and shadow patterns. Resolution is typically 5-20 centimeters for modern high-frequency systems, enabling detailed object detection.

2. Frequency, Range, and Coverage

Multibeam sonar vs side scan operate at different frequencies with contrasting coverage characteristics:

Multibeam systems typically operate at 95-400 kHz depending on water depth and required resolution. Shallow-water systems (50-500 kHz) cover 1-2 times the water depth swath; deepwater systems (12-100 kHz) cover 4-6 times the water depth. A 50-meter water depth covered by a deepwater multibeam might generate a swath 250-300 meters wide, with depth measurements every 1-5 meters across-track.

Side scan sonar operates at higher frequencies (200-1200 kHz for shallow-water systems; 100-500 kHz for deepwater systems). Coverage extends 4-10 times the water depth from the sonar fish (sometimes 300-500 meters total lateral distance in deeper water). Resolution is determined by frequency and signal processing, typically yielding centimeter-scale discrimination of seafloor features but without depth information.

3. Vertical Resolution vs Lateral Resolution

Multibeam versus side scan sonar excel at different spatial axes:

Multibeam provides excellent vertical resolution (±0.3-1 meter depending on system and depth) and good lateral resolution (1-5 meters depending on coverage area and sonar frequency). The trade-off: to cover large areas with good lateral resolution, vertical detail in intermediate depths may degrade.

Side scan provides excellent lateral resolution (5-20 centimeters for modern systems) enabling detailed object discrimination but provides no vertical (depth) information. A buried pipeline or submerged wreck appears in high-fidelity imagery but without depth context unless combined with multibeam or direct depth measurement.

4. Backscatter and Material Classification

Multibeam vs side scan sonar both capture backscatter (acoustic reflection intensity) but interpret it differently:

Multibeam backscatter is relatively weak and angle-dependent. Steep incidence angles (shallow water) produce different intensity signatures than grazing incidence angles (deeper water). Advanced processing normalizes backscatter variations, but the fundamental relationship between intensity and material type requires calibration and experience.

Side scan backscatter is the primary data product. Grayscale intensity reflects material acoustic impedance: strong reflections from rock, pipe, metal objects appear bright; soft sediments appear dark. Shadows behind objects aid interpretation. Side scan imagery is more intuitive for human interpretation than multibeam backscatter.

5. Cost and Operational Complexity

Multibeam sonar vs side scan differ significantly in cost and operational requirements:

Multibeam systems range AUD $300,000–$2,000,000+ depending on frequency range, swath width, and processing sophistication. Setup requires motion reference units (pitch, roll, heave compensation), sound velocity profilers, and sophisticated data processing software. Operators typically require training on bathymetric principles and quality assurance procedures. Daily operational costs (vessel charter, crew, processing) are high but amortized across large survey areas.

Side scan sonar equipment ranges AUD $50,000–$500,000 depending on frequency and range. Setup is simpler: tow a fish behind the vessel, monitor real-time imagery on deck. Operators require less formal training; imagery interpretation is more intuitive than processing bathymetric grids. Daily costs are lower, making side scan economical for small-area surveys or targeted object detection.

Multibeam Echo Sounder vs Side Scan Sonar: Applications

The choice between side scan sonar vs multibeam echo sounder depends on survey objectives:

Multibeam Echosounder Applications

Multibeam is the standard tool for bathymetric surveys, seabed mapping, and projects requiring precise depth data. Typical applications include port dredging surveys (measuring sediment volumes before and after excavation), offshore wind farm site assessment (foundation design requiring detailed bathymetry), pipeline route design (optimizing path around natural obstacles), and environmental baseline surveys (establishing seafloor topography for impact assessment).

Multibeam excels when the survey objective is “what is the shape and elevation of the seabed?” The resulting bathymetric contours guide engineering design, regulatory compliance, and project planning.

Side Scan Sonar Applications

Side scan sonar is preferred for object detection, seabed imaging, and searches where visual identification is paramount. Typical applications include wreck location and characterization, subsea pipeline and cable detection, buried object identification, unexploded ordnance (UXO) surveys, geohazard recognition (exposed rocks, seafloor discontinuities), and search and rescue operations.

Side scan excels when the survey objective is “what is present on the seabed and where?” The resulting imagery enables identification and geo-location of specific features, obstacles, and hazards.

Integration Strategy: Combining Multibeam and Side Scan Sonar

In practice, offshore surveys often integrate both technologies:

A phased approach uses multibeam sonar for broad-area reconnaissance, establishing bathymetry and overall seabed character across the project area. Areas of interest or potential hazard are then surveyed with high-frequency side scan sonar to confirm object identity, assess size and shape, and verify hazard type.

This integration reduces total survey cost by 20-40% compared to full-coverage side scan surveys while improving confidence in hazard identification. For example, a pipeline route survey might use multibeam over the entire 200-kilometer corridor to establish bathymetry and identify obvious seabed obstacles, then apply side scan sonar to 20-30 kilometers of intermediate and high-risk zones for detailed object detection.

Multibeam vs Side Scan Sonar in Shallow Water

Water depth influences equipment selection. In shallow water (5-20 meters), multibeam versus side scan sonar each have advantages and constraints:

Multibeam systems in very shallow water often suffer from wide swath widths and poor vertical resolution due to geometric constraints. A multibeam operating at 400 kHz in 10 meters of water might generate a 40-60-meter-wide swath with degraded lateral resolution. Modern shallow-water multibeams (500+ kHz) overcome this with narrow swaths and centimeter-scale resolution.

Side scan sonar in shallow water adapts easily, using higher frequencies (500+ kHz) to maintain resolution. Swath width remains proportional to depth, but this is less problematic for focused surveys of channels, harbors, or nearshore zones. Side scan sonar’s simplicity and cost-effectiveness make it popular for shallow-water applications.

Multibeam Sonar vs Side Scan: Decision Framework

Choosing between multibeam sonar vs side scan requires evaluating:

• Survey Objective. If the primary goal is bathymetric mapping and depth-based design decisions, multibeam is essential. If the goal is object identification and detailed seabed imaging, side scan sonar is appropriate.
• Project Scale. Large-area surveys (>50 square kilometers) favor multibeam for cost-efficient broad coverage. Small-area targeted surveys (<10 square kilometers) favor side scan for lower operational cost.
• Shallow vs Deep Water. Shallow water (5-50 meters) suits side scan sonar or high-frequency multibeam. Deepwater (>100 meters) suits mid-to-low-frequency multibeam for penetrating the water column and achieving large swath widths.
• Hazard Type. Buried subsea infrastructure and submerged objects require side scan sonar or targeted multibeam inspection. Natural seabed hazards (steep slopes, sediment instability) require multibeam for topographic context.
• Budget and Timeline. Side scan sonar surveys are faster and cheaper for small areas. Multibeam surveys are more cost-effective for large areas and provide additional depth data reusable for multiple purposes.

Best Practice: Multibeam and Side Scan Integration

Modern offshore surveying deploys integrated approaches combining both technologies:

AUV-based bathymetric multibeam reconnaissance over the entire project area establishes baseline seabed elevation, identifies major obstacles, and flags zones requiring detailed investigation. 

Vessel-based side scan sonar surveys targeted high-risk zones, confirming hazard identity and assessing object scale. This phased methodology reduces total survey cost by 30-40% compared to full-coverage side scan surveying while delivering comprehensive hazard identification and bathymetric context.

How QOffshore Sequences Multibeam and Side Scan Sonars to Maximize Survey Value

QOffshore is a Perth-based hydrospatial surveying and offshore engineering consultancy specializing in integrated sonar survey strategies that deploy both multibeam bathymetry and side scan sonar in complementary phases. 

Rather than choosing one technology, we sequence both: multibeam reconnaissance establishes broad-area seabed topography and identifies zones of interest, then targeted high-frequency side scan sonar provides centimeter-scale object detection and hazard confirmation in high-risk areas. 

This strategic pairing reduces total survey costs by 30-40% compared to full-coverage side scan surveying while maintaining bathymetric context essential for design and operational decision-making.

Whether you’re planning cable routes, assessing seabed hazards, or conducting comprehensive subsea characterization, our team optimizes multibeam and side scan deployment to match your investigation objectives and risk profile. 

Learn more at qoffshore.com, or contact us to discuss your multibeam echo sounder vs side scan sonar requirements and integrated survey strategy.

Key Takeaways

• Multibeam echo sounder provides 3D bathymetric depth data per IHO S-44 standards across a wide swath; side scan sonar provides 2D high-resolution imagery without depth measurements
• Multibeam covers 4-6 times the water depth swath; side scan covers similar horizontal range but with meter-scale depth resolution versus centimeter-scale lateral resolution
• Multibeam cost ranges AUD $300,000–$2,000,000+ equipment plus AUD $5,000–$15,000/day operations; side scan ranges AUD $50,000–$500,000+ equipment plus AUD $2,000–$8,000/day operations
• Multibeam excels for bathymetric surveys, route design, and seabed characterization; side scan excels for object detection, wreck location, and hazard imaging
• Integration of multibeam reconnaissance plus targeted side scan sonar reduces total survey cost by 30-40% while improving hazard confidence
• Shallow-water surveys (<50m) favor side scan sonar or high-frequency multibeam; deepwater surveys (>100m) favor mid-frequency multibeam for swath width and seafloor clarity
• Decision framework: balance survey objective, project scale, water depth, hazard type, budget, and timeline to select appropriate technology