Multibeam Echo Sounder
Remote sensing using a Multibeam Echo Sounder (MBES) is a well-established tool in the suite of underwater archaeological sensor techniques. Within the AMZ cycle, MBES can be used in the exploratory and valuation phases of field research on waterbeds, as well as for monitoring known underwater heritage sites.
What?
How does it work?
The Multibeam Echo Sounder (MBES) is an acoustic underwater sensor technique used to map the depth of the seabed (figure 1, left). This sensor, known as the “transceiver,” functions by simultaneously emitting multiple beams of sound waves underwater, which are then captured upon reflecting off the seafloor. The result is a high resolution point cloud of the waterbed (figure 1, right). This technique is standard in the maritime sector for creating depth models of the seabed and constructing detailed 3D models of features such as shipwrecks.

In-depth explanation X
The MBES is an advanced depth sounder that records water depth perpendicular to the direction of travel in multiple individual beams (up to 1,024). By measuring in parallel survey lines, it creates a full-coverage depth model (point cloud) of the seafloor. This technique is effective in fresh, salt, and brackish waters alike. Assigning colors to the various depth measurements allows for the creation of a color-coded depth map.
The MBES can be characterized according to the following parameters:
- Frequency: Ranging from 12 to 800 kHz, depending on the depth at which the seafloor is expected. For archaeological purposes, higher frequencies (between 400 and 800 kHz) are used to achieve higher resolution.
- Swath width: This refers to the width of the area being mapped. As a rule of thumb, the swath width is approximately 2.5 times the water depth below the transceiver.
- Beam width: Ranging from 0.3° to 3.0°; this is the opening angle of the sound beams received by the instrument. A narrower opening angle results in a narrower beam and more detailed data.
- Resolution: This depends on the frequency used and the water depth. In shallow areas (up to about 10 m depth), a resolution of 5 x 5 cm is achievable.
The swath width and resolution (footprint) depend on the water depth beneath the transceiver, the frequency used, and the width of the individual beams (figure 2).

What do you need?
An MBES is an expensive system that requires specialized knowledge. It cannot be used independently but relies on other systems, as outlined below. Essential components include the transceiver (transmitter/receiver), a positioning system, a motion sensor, and a Sound Velocity Probe. These are briefly described below:
- Transceivers(transmitter/receiver): These devices convert electrical signals into high-frequency acoustic signals and vice versa. The choice of transceiver affects the system’s coverage and resolution. The higher the frequency, the higher the resolution.
- Positioning System: A highly accurate positioning system (such as Real-Time Kinematic (RTK) GPS) is required to determine the position of the vessel and the MBES transceiver.
- Positioning Software: This software is needed to record the position of the vessel and the MBES transceiver.
- Motion Sensor: Necessary to capture all movement of the survey vessel, including roll, pitch, and heave (Image 3). Compensating for these movements is important to accurately calculate the position of the acoustic pulses.
- Sound Velocity Probe (SVP): The speed of sound in water depends on factors such as temperature, salinity, and pressure. The SVP is used to measure these parameters. After recording the raw data, it needs to be cleaned up using specialized software. This data cleaning is necessary to remove outliers and errors (spikes) caused by false echoes, schools of fish, or air bubbles in the water column.

Can be used with..
The MBES can be mounted on various platforms, each with its own advantages and disadvantages:
- Survey Vessels: These are suitable for larger water areas and large-scale surveys. A survey vessel can cover a wide swath in deeper waters (more than 20 meters), though the resolution decreases because of the increased distance from the seafloor, which results in a larger footprint.
- ROV (Remotely Operated Vehicle) or
AUV (Autonomous Underwater Vehicle): For detailed recordings in deep water, remotely operated or autonomous underwater vehicles can be deployed. The downside is that these are very costly.
Archaeological Applications
Place in the Dutch archaeological heritage management process
The MBES can be applied in the exploratory, mapping, and valuation phases of archaeological research on underwater sites (KNA Waterbodems protocol 4103, p. 5-7). The result is a point cloud or depth model of the seabed, comparable to a Digital Terrain Model (DTM). This can be used to visualize the seabed and the objects located on it.
What types of archaeological materials/landscapes
The MBES is used to map the underwater landscape, capturing details of objects on the seabed as well.
For this reason, MBES is particularly suited for mapping shipwrecks (see Figure 4). The technique provides precise depth data, allowing the shape and position of a wreck to be reconstructed. Details such as the ship’s hull, masts, and other structures can be clearly visualized.

Larger structures, such as submerged dikes, fields, or villages, can also be mapped using MBES by creating a composite mosaic from multiple recordings (figure 5).

In-depth explanation X
MBES can also be used to monitor the condition of underwater objects and landscapes by taking repeated recordings. This allows for the accurate tracking of changes over time, such as the condition and stability of shipwrecks or other underwater structures (figure 6).

Limitations/uncertainties
Here are some brief explanations of the limitations and uncertainties. A comprehensive discussion of all limitations and uncertainties is provided in the Marine Biodiversity Hub manual (Lucieer, 2018).
- Beam Divergence and Resolution: The resolution of MBES can decrease as the distance from the sensor to the seabed increases, particularly at the edges of the sound beam. This may lead to less accurate measurements in deeper areas or those located at the edge of the beam.
- Multiple Reflections: In shallow waters or when massive objects are present on the seabed, multiple reflections can occur, introducing noise into the data and complicating the interpretation of the images.
- Swath Width: The swath width is limited by the water depth. The maximum width of the area being measured is roughly 2.5 times the water depth beneath the transceiver. Thus, the swath width increases with depth, but this comes at the cost of resolution. Additionally, the movements of the platform can be compensated using a motion sensor.
- Environmental Factors: Changes in the seabed, such as sedimentation or erosion, can affect the results. These changes can vary over time, making periodic repeated surveys necessary to maintain accurate and up-to-date data.
References/further reading
Estumar. (n.d.). Dynamic positioning vessel in action. Estumar. https://estumar.com/es/blog/dp-vessel/. Accessed November 8, 2024.
Lucieer, V., Picard, K., Siwabessy, J., Jordan, A., Tran, M., & Monk, J. (2018). Seafloor mapping field manual for multibeam sonar. In R. Przeslawski & S. Foster (Eds.), Field manuals for marine sampling to monitor Australian waters (pp. 42–64). National Environmental Science Programme (NESP).
Van den Brenk, S., Opdebeeck, J., & Coenen, T. (2017). Monitoring scheepswrakken Burgzand Noord, Waddenzee, periode 1998–2017. DANS Data Station Archaeology. https://doi.org/10.17026/dans-22x-dq4h
Van den Brenk, S., Opdebeeck, J., & Coenen, T. (2017). Opnamen en monitoring historische scheepswrakken met hoge resolutie multibeam. Periplus Archeomare rapport 17A024-01. DANS Data Station Archaeology. https://doi.org/10.17026/dans-xkg-hmuz
Van den Brenk, S., Opdebeeck, J., & Muis, L. A. (2019). Monitoring historische vindplaatsen, 2013–2018: Het gebruik van geofysische opnamen voor archeologisch onderzoek. Rijksdienst voor het Cultureel Erfgoed. ISBN: 978 90 5799 321 3.
Van den Brenk, S. (2023). Monitoring scheepswrakken Burgzand Noord, Waddenzee, periode 1998–2023. Periplus Archeomare briefrapport 23A003-08.
Van Lil, R., & Van den Brenk, S. (2019). Inventariserend veldonderzoek (opwaterfase), Etersheim, Markermeer. Periplus Archeomare rapport 19A010-01.