The proposed PhD thesis topic: “Acoustic Non-Destructive Evaluation for Marine Archaeology and Submerged Infrastructure”
More than a thousand shipwrecks are known in the Baltic Sea, many of which still contain fuel, oil, or hazardous cargo. These wrecks continue to degrade over time due to progressive corrosion, yet their structural condition is often unknown. Regular inspection is severely constrained: visibility underwater is poor, manual diver-based surveys are costly, dangerous, and rarely feasible at depth. As a result, most wrecks are assessed only sporadically, and often only after environmental leakage becomes visible at the sea surface.
This doctoral project develops automated underwater acoustic inspection methods that enable non-contact characterization of submerged metallic structures using ultrasonic guided waves and acoustic arrays. The research focuses on extracting structural information from wavefields measured in water, with particular attention to corrosion detection and identification of internal liquid presence within wreck compartments. While shipwrecks in the Baltic Sea form the primary application scenario, the developed techniques are inherently general and applicable to offshore structures, ship hulls, flooded constructions, and underwater civil infrastructure.
The impact of the project lies in providing a scientific basis for future autonomous inspection systems for underwater structures, improving early detection capability, reducing inspection risk and cost, and supporting evidence-based environmental monitoring.
Scientific Background and Motivation
Assessing the condition of underwater archaeological sites, shipwrecks, and submerged infrastructure remains difficult because traditional inspection methods are constrained by poor visibility, access limitations, and the high cost and risk of diver operations. Sonar provides geometric information but cannot quantify corrosion or detect internal liquids, while contact-based ultrasonic thickness measurements require direct access and are impractical for large or hazardous structures.
Acoustic non-destructive evaluation using guided ultrasonic waves offers the potential for remote, wide-area sensing. Guided waves are inherently sensitive to corrosion, thinning, and fluid loading; however, their underwater application is fundamentally challenging. When structures are submerged, wave propagation is strongly altered by fluid–structure interaction, leading to energy leakage, dispersion changes, and increased attenuation.
A major scientific gap is that no unified physical or computational framework exists for interpreting guided waves in the presence of heavy fluid loading and complex environmental scattering. Rough, corroded surfaces, variable sound-speed profiles, bubble clouds, biological noise, and reflections from the free surface all produce distorted and multi-path wavefields that current NDE algorithms—developed for dry or contact conditions—cannot reliably interpret.
This PhD project addresses this gap by developing a physically informed and experimentally validated methodology for acoustic NDE in underwater environments, with shipwrecks in the Baltic Sea serving as the primary application. The broader motivation is to enable automated, non-contact inspection tools that can support marine archaeology, environmental monitoring, and the maintenance of submerged infrastructure.
Research Questions, Hypothesis and Work Plan
The central scientific hypothesis is that guided wavefields measured in submerged metallic structures contain sufficient information to estimate structural condition and internal fluid presence, provided that wave propagation mechanisms and fluid–structure interaction are adequately modelled and the signal processing framework is physically informed.
The research begins with finite-element modelling of guided ultrasonic waves in corroded plates under water, with and without internal liquid loading. These models are used to identify observable quantities related to thickness loss, scattering strength, modal conversion, and attenuation.
Building upon the modelling results, the project develops signal processing and imaging techniques for wavefield interpretation. These include mode separation, frequency–wavenumber analysis, energy-based mapping, and inversion techniques that aim to reconstruct thickness distributions or classify internal loading conditions. The robustness of these methods is studied under realistic conditions including measurement noise, incomplete scans, and environmental variability.
Experimental work is carried out using submerged steel samples with representative defect geometries. Ultrasonic transducers and acoustic arrays are used to measure wavefields in water under controlled laboratory conditions, followed by tests using robotic platforms in field environments. Numerical predictions and experimental data are continuously compared to refine both the physical models and inference algorithms.
The final phase of the work focuses on shipwreck structures as representative complex targets. The developed framework is tested on real cases where accessible, ensuring that the methods are grounded in practical constraints while remaining general enough for application to other underwater engineering structures.
Applicants should fulfil the following requirements:
Applicants should hold an MSc degree in engineering, applied physics, acoustics, or a related discipline and should demonstrate strong interest in wave physics, acoustic sensing, and quantitative non-destructive evaluation.
Essential qualifications:
- Experience with numerical modelling and programming (MATLAB, Python, or C++)
- Interest in wave physics, acoustics, or structural dynamics
- Good proficiency in written and spoken English
- Ability to work with experimental and simulated data
Highly desirable skills:
- Experience with ultrasonics, guided waves, or structural health monitoring
- Background in inverse problems, tomography, or computational imaging
- Familiarity with finite-element modelling
- Prior exposure to NDE, medical ultrasound, geophysics, or acoustics
- Interest in underwater systems, robotics, or marine technology
Motivation to work in interdisciplinary research involving modelling, experiments, and field measurements is expected.
Application procedure
The information for the PhD admission is available at TalTech´s web-page:https://taltech.ee/en/phd-admission
The following application documents should be sent to madis.ratassepp@taltech.ee
- CV
- Motivation letter
- Degree certificates asrequired by the university
- A research plan for the topic, including the overall research and data collection strategy
- Copy of the passport
Training and Research Environment
The doctoral student will be embedded in the Mechanics of Fluids and Structures research group at TalTech, working in close collaboration with the underwater acoustics and electronics research teams. The research infrastructure includes ultrasonic instrumentation, acoustic sensors, underwater measurement platforms, and high-performance computing facilities.
The project provides opportunities for:
- participation in international research visits,
- joint experiments with industrial partners,
- training in simulation, signal processing, inverse methods, and instrumentation,
- presentation of results at international conferences.
The candidate will receive supervision in experimental design, numerical modelling, academic writing, and research management. Collaboration with external partners ensures exposure to real-world problems and technology transfer contexts.
(Additional information)
For further information, please contact Dr Madis Ratassepp madis.ratassepp@taltech.ee and Dr Elizaveta Dubrovinskaya elizaveta.dubrovinskaya@taltech.ee
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