Recommendations for Utilizing Sonar Systems in Waterfront Facility Inspection and Assessment

Abstract: In the evolving landscape of marine engineering and underwater inspection, various sonar systems are increasingly requested and utilized for their potential to provide cost-effective, safely obtained, and highly detailed inspection data. Peering through turbid waters and creating highly detailed images, sonar systems can provide global perspectives that may otherwise not be achieved from diving alone. Sonar can also be utilized in currents much faster than a diver can safely negotiate, providing critical information while mitigating risk to the inspectors. However, these tools also have significant limitations that need to be understood and considered when planning, performing, and interpreting the results of underwater inspections. For example, sonar images are typically not detailed enough to identify finer defects such as steel surface corrosion. Heavy marine growth creates a textured appearance to sonar scan outputs, further limiting the user’s ability to identify deterioration.

This paper provides an in-depth analysis of sector-scanning, forward-facing, pipe-profiling, and side-scanning sonar systems as powerful tools to augment, rather than replace, in-person (diving) underwater inspections. Notably, the paper explores innovative techniques, such as streambed/seabed and soil profiling, intricate detailing of underwater structural deterioration, and integration of sonar data with topside and side view images to create multifaceted overviews of underwater and above-water structural components.

Through a presentation of multiple real-world applications, this paper offers a broad perspective on the capabilities and limitations of sonar systems as a structural inspection tool, with each case study implementing sonar imaging tools for a different purpose, structure type, and globally diverse location. Examined use cases include routine inspections, design-level inspections, post-construction inspections, sensitive aquatic vegetation surveys, and special inspections for concrete gravity walls, concrete block masonry walls, steel sheet pile mooring cells, sheet pile bulkheads, and concrete armor units. For each practical application, the sonar survey results are analyzed and directly compared against the findings of in-person inspections by engineer divers conducted in concert with and alongside the sonar survey.

This paper offers a summary of the capabilities and limitations of multiple sonar systems as well as diving inspections, clearly demonstrating that a variety of techniques are required to meet the varied challenges of underwater inspection. With this knowledge in hand, sonar operators, waterfront inspectors, ports and maritime engineers, and facility owners/managers can plan a well-rounded waterfront inspection program leveraging a combination of tools and techniques to best fit the goals and requirements of the required survey.

How does this project / topic contribute to the advancement of the industry and profession?: This paper provides practical comparisons of underwater inspection techniques as well as guidance on the capabilities and limitations of sonar. This will empower inspectors and facility owners to assess the capabilities and applicability of various sonar tools and make educated decisions on how best to assess and maintain existing maritime infrastructure.

Does the project / topic implement new and innovative techniques, materials, technologies, and delivery methods?: Yes, this paper presents novel applications of sonar systems for waterfront facility inspections and a unique direct comparison between Engineer-diver-generated field notes and sonar outputs.

What was the most challenging aspect of your project / topic and how did you handle it to ensure success?: The largest challenge when assessing the use of any novel underwater inspection tool is definitively determining the accuracy and completeness of the collected data. It is difficult to make meaningful comparisons of underwater inspection techniques from different survey efforts due to the diverse nature of marine structures and environments.

Directly comparing results of both sonar systems and divers from the same structure from the same inspection, this study removes the variability between marine structures/waterways while confirming the completeness of each generated data set. This paper provides a true “apples-to-apples” comparison and accurately demonstrates the capabilities and limitations of both techniques.

Who is the target audience for this paper?: The target audience includes anyone involved in managing, assessing, or rehabilitating maritime assets including Engineer Divers, Ports Engineers, Waterfront Asset Managers, and Facility Owners/Operators/Managers, and especially those scoping and performing underwater inspection.