Choosing the Right Bathymetric Survey Technology: Single Beam, Multibeam, or Aerial Bathymetric LiDAR?

In our previous article on Hydrographic vs. Bathymetric Surveys, we explored the difference between hydrographic and bathymetric surveys and how they help engineers, developers, and government agencies understand what lies beneath the water's surface.

Once you've determined that your project requires a bathymetric survey, the next question we receive regularly becomes: Which survey technology should you use?

Today, there are several technologies available to measure underwater terrain, each designed for different water depths, project sizes, environmental conditions, and engineering requirements.

The answer isn't simply choosing the latest or most advanced equipment. Instead, it is about selecting the technology that best fits your project's objectives.

Understanding how each system works and where it performs best can help ensure you receive the right data while optimizing project cost, efficiency, and accuracy.

One of the reasons we have invested in multiple bathymetric survey technologies is because every project presents a different challenge. A narrow river requiring periodic monitoring has very different survey requirements from a commercial port undergoing dredging, while a protected coral reef presents challenges that neither of those environments share.

Rather than recommending the same solution for every project, our approach is to first understand the project's objectives before selecting the technology that will provide the most accurate and cost-effective results.

There Is No "Best" Bathymetric Survey Technology

A common misconception is that one bathymetric technology is universally better than another.

In reality, every technology has its strengths and limitations.

Some of the first questions we ask our clients include:

• What is the purpose of the survey?

• How large is the project area?

• How deep is the water?

• Is complete seabed coverage required?

• Is the site environmentally sensitive?

• What level of detail is needed?

A narrow river requiring only a few cross-sections has very different survey requirements from a busy commercial port, while a shallow coral reef presents completely different challenges from either of these environments. Factors such as water depth, water clarity, project size, required detail, environmental conditions, accessibility, and project budget all influence which technology is most appropriate.

Rather than asking "Which technology is best?", project owners should instead ask: "Which bathymetric technology is best suited for my project?"

Single Beam Echo Sounder (SBES): A Reliable and Cost-Effective Solution

The Single Beam Echo Sounder (SBES) is one of the most established methods of conducting bathymetric surveys. In many ways, it can be compared to conventional topographic surveying on land.

Just as a Total Station collects one point at a time, a Single Beam Echo Sounder measures one depth point directly beneath the survey vessel with every acoustic pulse. The system works by transmitting a sound wave vertically toward the seabed. Once the pulse reflects from the bottom, it returns to the transducer mounted beneath the vessel. By measuring the travel time of the sound wave and applying corrections for the speed of sound in water the system calculates the water depth beneath the vessel.

As the survey vessel follows predetermined survey lines, thousands of individual depth measurements are collected. These measurements are then combined to create a model of the underwater terrain. Because each acoustic pulse produces only one depth measurement, the quality of the final seabed model depends heavily on the spacing between survey lines. Areas between these lines are interpolated rather than directly measured, making survey planning particularly important.

At AB Surveying, we typically recommend Single Beam Echo Sounders for projects where complete seabed coverage and a highly detailed data is not required.

For example, river cross-sections, inland waterways, irrigation canals, reservoirs, and preliminary engineering investigations can often be completed efficiently using this technology.

Their relatively simple operation, reliable performance, and lower mobilization costs continue to make them a widely used solution for many inland and freshwater applications.

Multibeam Echo Sounder (MBES): Complete Seabed Coverage

While Single Beam Echo Sounders collect one measurement at a time, Multibeam Echo Sounders (MBES) dramatically increase both coverage and data density.

Similar to a Single Beam Echo Sounder, a Multibeam Echo Sounder also measures water depth using acoustic pulses. The key difference is that instead of transmitting a single beam directly beneath the survey vessel, it emits hundreds of acoustic beams simultaneously in a fan-shaped pattern. Each beam measures a different point on the seabed, allowing the system to capture an entire swath of underwater terrain with every pass, producing a dense three-dimensional point cloud of the seabed, similar in concept to how LiDAR creates a point cloud on land.

Multibeam Echo Sounders are particularly well suited for deeper water environments, often operating effectively at depths of up to 500 metres. As water depth increases, the swath width also expands, allowing larger areas of the seabed to be covered efficiently with each survey line.

For example, when assisting clients involved in port developments or dredging projects, engineers often need accurate seabed models to calculate dredging volumes, identify underwater obstructions, and plan construction activities with confidence.

In these situations, Multibeam surveys provide far greater certainty than technologies that rely on interpolation between survey lines.

However, in very shallow water environments, Multibeam surveys are not always the most practical option. Navigating a survey vessel in shallow areas can increase the risk of grounding, and in environmentally sensitive zones, vessel-based operations may also be considered intrusive.

In these situations, alternative technologies such as Single Beam Echo Sounders or Aerial Bathymetric LiDAR may provide a more suitable and less invasive solution.

This makes Multibeam Echo Sounders particularly valuable for projects where accuracy and complete coverage are critical.

Typical applications include:

• Port and harbor developments

• Dredging projects

• Navigation channel surveys

• Offshore infrastructure

• Bridge and marine engineering

• Underwater pipeline and cable corridors

Because Multibeam systems collect significantly more data than Single Beam systems, they also require more sophisticated positioning systems, careful sound velocity corrections, and advanced processing workflows.

Although Multibeam surveys generally involve higher mobilization and processing requirements than Single Beam systems, the additional information often translates into better engineering decisions and reduced project risk.

For our clients, this means greater confidence that the underwater terrain has been comprehensively mapped, reducing uncertainty during design, dredging, and construction while minimizing the risk of unexpected conditions being discovered later in the project.

Aerial Bathymetric LiDAR: When Boats Are No Longer the Best Option

Not every underwater environment can be efficiently surveyed using a boat.

Some of the most challenging projects we encountered involve very shallow waters, environmentally sensitive areas, coral reefs, river mouths, or coastlines where navigating a boat may be difficult, inefficient, or undesirable.

This is where Aerial Bathymetric LiDAR provides a unique advantage.

Unlike echo sounders that rely on acoustic waves, Bathymetric LiDAR uses a green laser mounted on an aircraft. Green wavelengths have the unique ability to penetrate clear water, allowing the system to measure both the water surface and the seabed below.

As the aircraft flies across the project area, millions of laser pulses are transmitted toward the ground and water surface. By analyzing the time it takes for the laser pulses to return from both the water surface and the seabed, the system calculates water depth while simultaneously capturing topographic information on adjacent land.

One of the greatest advantages of Bathymetric LiDAR is its ability to collect continuous land and underwater data within a single survey campaign.

Rather than stopping at the shoreline, engineers receive a seamless terrain model extending from dry land to the submerged environment. This capability is particularly valuable for coastal engineering, shoreline management, river studies, and environmental monitoring.

When discussing projects with our clients, we often recommend Aerial Bathymetric LiDAR where vessel access is limited or where minimizing environmental disturbance is an important consideration.

Aerial Bathymetric LiDAR is commonly used for:

• Coral reef mapping

• Coastal engineering

• Shoreline monitoring

• River surveys

• Environmental assessments

• Shallow coastal waters

• Protected marine areas

  
  

However, Bathymetric LiDAR also has important limitations.

Its performance depends heavily on water clarity, turbidity, wave conditions, and water depth. In highly turbid or deep waters, laser penetration decreases, making sonar-based technologies more suitable.

Comparing the Technologies

Imagine three different projects.

The first involves surveying a narrow river to establish cross-sections for flood modelling. In this case, a Single Beam Echo Sounder may provide all the information required while keeping survey costs economical.

The second project involves expanding a commercial port where engineers require detailed information about the entire seabed to support dredging and navigation. Here, a Multibeam Echo Sounder would be the preferred solution because of its ability to capture complete seabed coverage and highly detailed terrain models.

The third project focuses on mapping coral reefs and shallow coastal waters where vessels cannot safely navigate without disturbing sensitive marine habitats. In this situation, Aerial Bathymetric LiDAR offers the ability to efficiently collect both land and underwater data without requiring a survey vessel.

Each technology is designed to solve a different surveying challenge.

The Survey Technology Is Only Part of the Solution

One misconception we occasionally encounter is that the survey equipment alone determines the quality of the final deliverables.

In reality, selecting the right technology is only the beginning.

Successful bathymetric surveys depend not only on selecting the right technology but also on proper survey planning, experienced hydrographic personnel, accurate positioning systems, appropriate survey platforms, and rigorous data processing.

For vessel-based surveys, the stability of the survey platform itself also contributes to data quality.

At AB Surveying, we conduct our hydrographic operations using a dedicated company-owned survey vessel designed to support professional marine surveying. This allows us to deploy the most appropriate survey technology while maintaining stable data acquisition throughout the project.

Ultimately, even the most advanced equipment can only perform as well as the team planning, operating, and processing the survey.

Choosing the Right Bathymetric Survey Technology

Every bathymetric survey is different.

Selecting the right technology involves balancing several considerations, including:

• Water depth

• Water clarity

• Required survey detail

• Project size

• Accessibility

• Environmental conditions

• Required deliverables

• Project timeline

• Budget

A narrow river requiring annual monitoring has very different objectives from a commercial port preparing for dredging works or a coastal engineering project mapping sensitive coral reef ecosystems.

Rather than recommending one technology over another, our role is to evaluate the project as a whole and determine which approach or combination of approaches will provide the information engineers actually need.

In some projects, a Single Beam Echo Sounder provides the most practical solution.

In others, complete seabed coverage from a Multibeam Echo Sounder becomes essential.

For shallow coastal environments, Aerial Bathymetric LiDAR may provide capabilities that neither vessel-based technology can offer on its own.

It's also important to recognize that these technologies are not always used independently. In many projects, combining two or more bathymetric survey technologies provides the most complete understanding of the site. For example, Aerial Bathymetric LiDAR may be used to map the shoreline and shallow coastal waters, while a Multibeam Echo Sounder surveys deeper areas beyond the laser's effective range. Integrating these datasets allows engineers to work with a seamless representation of the environment from land to deeper water. We'll explore this integrated approach in more detail in a future article.

The right answer depends on the project not the equipment and the most suitable solution is rarely determined by a single factor.

Instead, experienced hydrographic surveyors evaluate the project as a whole before recommending the technology or combination of technologies that will provide the most accurate and cost-effective results.

Final Thoughts

There is no universal solution for every bathymetric survey.

Single Beam Echo Sounders continue to provide a reliable and economical solution for many preliminary surveys.

Multibeam Echo Sounders offer complete seabed coverage and detailed three-dimensional mapping for complex marine engineering projects.

Aerial Bathymetric LiDAR provides unique capabilities in shallow, clear waters where traditional vessel-based surveys may be difficult or impractical.

Understanding the strengths and limitations of each technology allows project owners to make informed decisions and select the approach that best meets their project's objectives.

Choosing between Single Beam, Multibeam, and Aerial Bathymetric LiDAR is not about selecting the most advanced technology.

It is about selecting the technology that best aligns with the project's objectives, environment, engineering requirements, and budget.

At AB Surveying, we believe successful bathymetric surveys are not defined by using the most advanced equipment. They are defined by selecting the right technology for the right environment. By understanding each client's objectives before recommending a solution, we help deliver reliable data that supports sound engineering decisions and long-term project success.

By combining technical expertise with the appropriate survey technology, we help our clients obtain reliable data that supports sound engineering decisions, reduces project uncertainty, and lays the foundation for safer, more efficient, and more successful projects.

Not sure which survey your project requires?

Our team is here to help you identify the right surveying solution for your needs.

📩 info@absurveyingph.net

🌐 www.absurveyingph.net

About AB Surveying & Development

Since 1998, AB Surveying & Development has been pushing the boundaries of the surveying industry.

The latest technology that we pioneered (LiDAR Surveying), has revolutionized several industries within the Philippines. By reducing fieldwork by as much as 95% while increasing precision and reliability of the data acquired, our clients can now develop faster, and with more confidence.