Marine geophysical surveys: a guide to their benefits

Types of Surveys

Marine geophysics employs various surveying techniques to map and analyse seafloor conditions. These surveys allow us to identify sediment layers, buried objects, and other features of interest to support nautical charting, offshore infrastructure projects such as wind farms and monitor environmental changes.

Key survey types include:

• Seismic Surveys – Utilising controlled energy sources to map and investigate the subsurface layers of the seafloor and identify potential hazards.

• Gravity and Magnetic Surveys – Measuring variations in seabed's gravity and magnetic fields to detect underwater basins, ridges and mineral deposits at large depths.

• Sub-Bottom Profiler - Detects sediment layers and rocks beneath the seabed using a sonar-like system.

• Resistivity and Electromagnetic (EM) Surveys – Measures variations in the electrical conductivity of the seafloor, which is useful for identifying hydrocarbon reservoirs or gas hydrates.

• Multibeam Bathymetry - Uses sonar to create an underwater topographic map, the data collected provides a high-resolution 3D model of the seafloor.

• Side-Scan Sonar - Uses sonar to create a detailed image representation of the seabed and subsurface conditions.

• Hydrographic Surveys - Combines various marine survey types to give a thorough analysis of large areas of ocean, including water depth, seabed features and sub-bottom anomalies.

Other forms of geophysical surveys, such as Ground Penetrating Radar (GPR), cannot be used in marine environments. This is because GPR uses radio waves to locate underground features, which are quickly absorbed by the high conductivity of seawater. Whilst effective in freshwater environmental projects such as river basin management, it's difficult to obtain useful subsea information using GPR due to limited penetration depth.

Seafloor Mapping Techniques & Vessels

Most commonly, geophysical surveys are used to create high-resolution topographic maps of the seafloor.

Hull-mounted sensors such as multibeam echosounders can be attached to vessels, including remote and autonomous vehicles, to map large areas efficiently. Our Hydrodynamic Acquisition System (HAS) reduces the need to drydock our survey vessels to install this equipment, allowing crews to mobilise in days instead of weeks.

Side-scan sonar, magnetometer sensors and sub-bottom profiler systems, such as the Innomar deep-36 system, are towed through the ocean via an automated winch. These travel with a vessel within meters of the seafloor.

Long-range drones can also be used in a marine environment, equipped with survey equipment for detailed geophysical analysis on marine conditions. Fugro have a global network of 8 remote operations centres, removing the need for crew on the ground and helping ensure the safety of your engineering project.

Data Analysis and Interpretation

Geophysical surveys provide us with powerful datasets and all the information we need about a given location, whether land or marine. Data collection is just the beginning; real value is added when the data is analysed and interpreted effectively.

Analysis is what paints the picture of the marine environment, identifies potential hazards and any geological features that could hinder offshore construction and other marine activities. Not only that, but analysis allows us to quality control and access the reliability of the data.

Interpretation allows us to inform project managers for better resource planning and risk management.

With a global team of geophysical survey experts, Fugro can provide you with geological insights into large marine areas. As well as specialist advice, we give you access to VirGeo®, a cloud-hosted, web-based Geo-data engagement platform.

With VirGeo®, you’ll have all your geophysical survey data in one place. See how your project is progressing, plus get early insights and real-time results for on-time milestone achievements.

Marine Geophysics in Action

Identifying Buried Objects in Scotland

In 2022, Fugro were conducting a detailed seabed survey for the MarramWind offshore wind farm when we uncovered a previously unchartered shipwreck. Depth readings from the multibeam echosounder (MBES) showed a vessel approximately 100 metres in length. Meanwhile sub-bottom profiler (SBP) data revealed layers of disturbance consistent with a major solid object buried in the seabed.

Preserving Norway's Seabed with Multibeam Bathymetry

Fugro have been working on the MAREANO seabed mapping project, aiming to map oceans for responsible management and preservation of Norway's marine resources. Having been actively involved in the project since 2006, we have acquired over 142,000km2 of data to support Norway's offshore infrastructure and coastal resilience processing.

Supporting Nearshore Development in the Arabian Gulf with Seismic Surveys

Unmanaged geo-risks are known to negatively impact project cost and schedule during construction. In a nearshore environment, geo-risks are more common due to the shifting tide pattern and effect climate change is having on sea level and coastlines.

Our client wanted to construct an artificial island off the coast of the Arabian Gulf and asked us to support with research, data and insights. We conducted a seabed and sub-seabed marine geophysical survey to ensure economic and timely development and to minimise ecological disruption. This seismic survey covered 1,270,000 m2 of shallow, nearshore environment - with an 85% reduction in data collection time compared to traditional survey methods.