Seeing Beneath the Waves: How Ultra-High Resolution Seismic De-Risks Offshore Wind Foundations

As offshore wind energy scales up to meet global renewable targets, the engineering complexity grows exponentially. Beyond the challenges of larger turbines and harsh weather, a critical factor lies hidden beneath the seabed: geological hazards. Ensuring the safety of personnel, the integrity of multi-million-pound structures, and the efficiency of construction hinges on accurately characterizing the sub-seafloor.

Fraunhofer IWES is at forefront of applying ultra-high resolution multichannel seismic (UHR MCS) technology, a cutting-edge geophysical technique delivering the sub-meter clarity needed to identify these hazards, mitigate risks, and support smarter decisions throughout the offshore wind project lifecycle.

The Regulatory Imperative: Knowing the Ground Below

Identifying geological hazards isn't just good practice; it's a regulatory requirement. Standards like ISO 19901-10:2021(E) mandate seismic surveys for mapping sub-seafloor conditions. In Germany, the Federal Maritime and Hydrographic Agency (BSH) requires a comprehensive site investigation process for offshore wind farm approval, including:

• Desk Study: Reviewing existing data to identify known hazards.
• Hydrographic Survey: Mapping water depth and marine characteristics.
• Geotechnical Survey: Assessing seabed material properties.
• Geophysical Survey: Providing detailed images of subsurface structures.

The goal is to demonstrate structural integrity, a crucial step for gaining project approval. UHR and even Ultra-Ultra-High Resolution (UUHR) seismic methods play a key role in the geophysical component.

Why Offshore Wind Needs a Different Seismic Approach

Multichannel seismic methods, refined over decades in the oil and gas industry, have been adapted for offshore wind. However, the requirements are vastly different. While hydrocarbon exploration targets structures kilometers deep, offshore wind focuses intensely on the top 100 to 200 meters of the seabed. Developers need to identify geological features at meter and sub-meter resolution – details critical for foundation design and installation safety.

UHR MCS achieves this by:

• Using high-frequency seismic sources (mini air guns, sparkers, boomers).
• Employing an array of closely spaced receivers (hydrophones) to detect reflected acoustic waves.
• Recording data from multiple channels simultaneously to create detailed 2D or 3D images of the subsurface.

Fraunhofer IWES utilizes a customized, modular acquisition system that can be tailored (e.g., source type, receiver spacing) to meet specific client needs for depth penetration and spatial resolution, ensuring the precise imaging required for wind farm engineering.

From Data Acquisition to Actionable Ground Models

The process involves several key stages:

1. Survey Campaign: UHR MCS data is acquired offshore, based on careful planning informed by client needs and existing geological knowledge.
2. Data Processing: Onshore, advanced techniques filter noise, remove artifacts, and enhance image clarity.
3. Interpretation: Expert geologists meticulously interpret the processed data to identify geological structures.
4. Integration & Ground Modeling: The UHR MCS data is integrated with hydroacoustic and geotechnical data to build comprehensive ground models.

These ground models are essential for understanding:

• Seafloor topography and water depth.
• Sediment layering and lithological changes.
• Potential obstructions like boulders or Potential Unexploded Ordnance (PUXO).
• Structural features such as faults or buried channels.
• The presence of shallow gas or weak organic-rich layers.
• Sediment composition (sand, silt, clay) and properties (grain size, permeability, consolidation state) crucial for foundation design.

With experience covering thousands of kilometers of marine seismic data annually, Fraunhofer IWES provides the high-quality data and interpretation necessary for reliable geological characterization.

Impact Across the Project Lifecycle

Identifying geological hazards early using UHR MCS has far-reaching benefits beyond the initial design phase:

• Informed Construction Planning: Detecting hazards like buried channels or unstable soils allows engineers to modify foundation designs (pile diameter/length) or select alternative installation methods proactively, mitigating risks like pile refusal or equipment damage.
• Reduced Delays & Costs: Addressing potential obstacles before construction begins helps avoid costly delays and budget overruns.
• Long-Term Stability: Understanding geological processes and sediment properties enables the design of foundations capable of withstanding environmental forces over the turbine's lifespan.
• Optimized Cable Routing: Detailed sub-seafloor insights facilitate the planning of the most efficient and secure routes for inter-array and export cable installation.
• Targeted Geotechnical Sampling: High-resolution seismic data allows for more precise targeting of geotechnical boreholes and sampling, significantly reducing the need for extensive, intrusive, and costly drilling campaigns.
• Minimized Environmental Impact: Reducing the scope of geotechnical investigations lessens the environmental footprint of site assessments.

Conclusion: Precision Geophysics for a Safer, Greener Future

Accurate geological characterization is non-negotiable for the safe and efficient development of offshore wind farms. UHR multichannel marine seismic surveys provide the necessary detail to understand subsurface conditions, identify potential hazards, and make informed decisions from initial design through to long-term operation.

By enabling precise ground models, optimizing foundation and cable route design, and reducing the need for extensive intrusive investigations, this advanced geophysical approach leads to safer operations, reduced costs, and more efficient project timelines. As offshore wind continues its vital expansion, integrating cutting-edge technology and expertise from research institutes like Fraunhofer IWES will be essential for building a resilient and sustainable clean energy future.