Abandoned Anchor Chain Detection and Subsea Power Cable Survey

For this project, BM was tasked with conducting a subsea survey, under highly challenging environmental conditions, with extremely poor visibility below 0.5 meters, in murky waters and over an argillaceous clay seabed. The objective was to search, detect, and document an abandoned anchor chain and assess its possible interaction with submarine power cable infrastructure.

The operation covered an area of approximately one square kilometer. Due to the extremely low visibility, the Multibeam Imaging Sonar (Oculus M750d) was employed as the sole search method, with systematic flybys at altitude used to scan the seabed for potential targets. The abandoned chain was first detected at a standoff distance of approximately 50 meters, after which the sonar provided continuous guidance during the approach, remaining effective even at close range under the prevailing conditions.To ensure accurate geolocation, the ROV (Deep Trekker Revolution Nav Package) was also equipped with a USBL positioning system (Blueprint Subsea SeaTrac), which provided precise subsea coordinates for all detected objects.

Following the detection of the chain, the survey focus shifted to evaluating its possible impact on the nearby submarine power cable routes. Imaging sonar records were analyzed to identify seabed markings consistent with chain movement and to trace the route of the power cables. This allowed our team to identify and map possible chain-to-cable interaction points, including areas where cable displacement appeared to have occurred. These findings were further validated through the ROVs video footage, which provided direct visual confirmation despite the difficult environmental conditions.

All results were consolidated into a comprehensive reporting package. The integration of Multibeam Imaging Sonar, USBL, and ROV video data produced a geospatial dataset that tied every observation to precise subsea coordinates. From this dataset, annotated images, detailed maps, and extracted video sequences were generated to illustrate the key findings. The final deliverables provided stakeholders with a technically reliable and evidence-based foundation for subsequent review and analysis.

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