Author: Rosie O’Connor, Data Scientist 

From Snapshot Surveys to Continuous Oversight: Closing the Data Gap on Depth of Burial

Since early in Offshore Wind, the standard protocol for subsea cable management has relied on periodic Remote Operated Vehicle (ROV) or geophysical surveys. Typically conducted every two to five years, these campaigns provide high-resolution visual and bathymetric data, but they suffer from a fundamental flaw; they are snapshots in time. In a dynamic subsea environment where sand waves can migrate several metres in a single season and storm events can cause rapid scouring, a survey is often out of date before the data has even been processed.

This “snapshot” approach puts operators in a reactive cycle. When a survey finally reveals an exposed cable or a dangerous free-span, the risk has likely been present for months or even years, leading to accumulated mechanical fatigue and prolonged exposure to external threats. For an export cable, where failure costs range between £8M and £24M due to downtime and emergency repairs, being “in the dark” is no longer an acceptable operational risk.

The Power of Continuous Monitoring

By integrating Distributed Acoustic Sensing (DAS) via the Scattersphere® platform, Indeximate® fills the critical gaps between these physical inspections. Rather than waiting years for the next vessel deployment, DAS turns the cable into a permanent, 24/7 sensor that monitors environmental change in real-time. This is achieved by repurposing the “dark” fibres already present within the cable, effectively transforming the infrastructure into its own monitoring device without the need for additional subsea hardware.

While an ROV tells you where the seabed is today, DAS tells you how it is moving. By tracking the cable’s thermal and acoustic response, we identify the exact moment burial depth begins to decrease, allowing operators to understand the magnitude and velocity of seabed migration. This provides a four-dimensional view of the asset—mapping exactly where deburial risk is developing and how it is evolving over time.

Visualisation of cable in various burial states

The Mechanics of Burial Detection

To provide this level of detail, the Scattersphere® platform employs a sophisticated algorithmic approach to verify burial and detect exposure. While our system can detect significant changes in the cable’s environment independently, we can achieve even higher levels of accuracy by using previous ROV surveys to “ground-truth” the data.
By benchmarking the acoustic energy recorded by DAS against known burial depths from a historical survey, we create a calibrated model of the cable’s specific environment. This allows us to use the ROV as a reference point to monitor the changing condition of the cable over time. Even without a recent survey, our algorithms can detect the characteristic acoustic signals that occur when a cable is shielded by sediment or becomes exposed to tidal currents. This means that while historical data enhances precision, the system remains a powerful tool for identifying exposure in the absence of current ROV runs.

Example of the Cable Depth of Burial risk metric displayed on the Scattersphere

Triggered vs. Scheduled Inspections

Continuous monitoring allows for a fundamental shift to “Condition-Based” Maintenance. The traditional model of commissioning a costly vessel on a fixed three-year schedule is inherently inefficient; it often results in surveying buried cables that don’t need inspection or missing exposed cables that do. With Indeximate’s service, owners can use DAS data to trigger an inspection only when a specific change threshold is met.

Conversely, if the data shows the cable remains securely buried and stable, expensive surveys can be safely deferred. This “Informed Control” moves the financial burden from a fixed OPEX cost to a targeted, strategic investment. By extending survey intervals and only deploying assets when the data confirms a risk, operators can significantly lower the lifetime cost of cable ownership while actually increasing the safety of the asset.

Precision in Remedial Works and Verification

When burial is required, our high-resolution spatial profiling identifies the precise metre-mark of concern. This allows for the surgical application of remedial actions, such as Controlled Flow Excavation (CFE), rather than blanket interventions across kilometres of cable.

Following a burial campaign, DAS provides immediate, metre-by-metre verification of the new burial depth. Because the platform can detect the drop in noise as the cable is covered, it offers real-time confirmation of the work’s success. This can replace the need for a follow-up “as-built” ROV survey, saving significant vessel time and providing instant peace of mind to both the operator and the contractor.

Eliminating Uncertainty and Securing Life Extension

The Scattersphere® provides a longitudinal health record, linking one ROV survey to the next with a continuous line of data. This eliminates the uncertainty of periods between surveys, ensuring that the asset’s burial status is never a matter of guesswork.

For operators of ageing assets, this chronological history is invaluable for life extension applications. Regulatory frameworks, such as the UK’s T-6 milestone, require empirical evidence of an asset’s condition to justify operation beyond its original design life. By maintaining a definitive health record of burial and integrity, Indeximate provides the objective data needed to satisfy the rigorous demands of insurers and regulators, securing the long-term value of these critical infrastructure investments.

Ultimately, the value lies in informed control. By using DAS to monitor change continuously, you are no longer just reacting to history; you are managing the future of your asset with spatial and temporal precision. We provide the clarity needed to make high-stakes decisions with confidence, ensuring that subsea cables—the backbone of our renewable energy transition—remain protected, productive, and profitable for their entire lifecycle.

Example of the Cable Depth of Burial 2D, Profile and location time series  in Scattersphere