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Improving the characterisation of railway trackbed materials through multi-fold Ground Penetrating Radar imaging

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  • Full or part time
    Dr R Clark
    Dr B Murphy
  • Application Deadline
    No more applications being accepted
  • Competition Funded PhD Project (European/UK Students Only)
    Competition Funded PhD Project (European/UK Students Only)

Project Description

Recent advances in ground penetrating radar (GPR) hardware have made it possible to collect high-resolution 3D volumes of data. Despite such systems becoming more commonplace, they are rarely deployed in multi-offset array configurations, acquiring multi-fold data. This project will apply that capability to the specific target of railway trackbeds, to resolve discrete objects and to derive physical properties of trackbed materials; characteristics needed to identify where trackbed integrity is jeopardised, e.g. by a reduction in elasticity under load, or blocked drainage pathways.

The multi-channel GPR array-based system, belonging to the CASE Partner, comprises 14 transmitters and 14 receivers at 15cm lateral intervals. The data are multi-offset in the cross-track direction, with 14-fold common-mid-point coverage at the array centre, reducing to single-fold at each end: effectively a short 2D profile. Data are then acquired at regular intervals in the along-track direction, resulting in a 3D data volume. This project will develop a seismic reflection style processing flow, such as in use for hydrocarbon exploration, with three specific objectives: Imaging: Accurate mapping of interfaces and detection of isolated metal objects within layered trackbed structure. Each individual multi-fold cross-track profile, and a single-fold along-track profile will be processed first, followed by the full 3D data volume. The processing will be designed to improve signal-to-noise ratio through stacking of move-out corrected data, reject airwave noise (particularly prevalent in data from the railway environment), and handle large volumes of data. Velocity Estimation: Stacking velocity analysis will yield velocity estimates for the trackbed layers as well as improved depth imaging. A quantitative and statistical analysis of the derived velocity model will permit a physical interpretation of the material properties, based on dielectric models of the track bed. Attenuation Estimation: The subsurface acts as a low-pass filter to EM wave propagation, leading to a broadening of the wavelet and a loss of resolution with depth. Quantification of the quality factor Q* will provide the ability to compensate for these effects and improve imaging of trackbed structure, and also provide an additional physical parameter that can be related to the conductivity of the trackbed materials.

The project will benefit from existing datasets and provide opportunities to gather new data and ground-truth information from active railway lines in various conditions, including full-size indoor and outdoor ‘test track’ facilities. The project will suit a physics, geophysics or other numerate geoscience graduate: computer literacy (ideally, LINUX and Matlab™) is necessary. Attending relevant Master’s-level modules (MSc Exploration Geophysics, MSc Engineering Geology) can form part of Year 1 training. Informal enquiries in the first instance should go to Dr Roger Clark, [Email Address Removed].

The School of Earth Sciences (SEE) supports strong undergraduate and taught-Master’s geophysics programmes, as well as research. It is exceptionally well resourced, with a sector-leading inventory of modern near-surface geophysical survey equipment, and commercial processing and analysis software (e.g. SeisSpace/ProMAX™). SEE is ranked 2nd in the UK for ‘research power’ (RAE 2008) and 3rd in the UK for ‘academic reputation’ (QS World Ranking 2013).

Funding Notes

This will be a NERC/DTP CASE Award with Zetica Ltd., http://www.zetica.com with Dr Brian Barrett at Zetica as co-supervisor . UoL/SEE and Zetica have a well-established collaborative relationship on previous projects. DTP projects are in competition for funding. Most EU candidates will only be eligible for a ‘Fees Only’ award including tuition fees and Research Training and Support Grant (RTSG), ie, it does NOT include a stipend. EU candidates who are eligible for a full award are normally those who have spent the 3 years immediately preceding commencement of the PhD in the UK.

References

Recommended Reading:
GRASMUECK, M., WEGER, R. & HORSTMEYER, H. 2005. Full-resolution 3D GPR imaging. Geophysics, 70, K12-K19.
GREAVES, R. J., LESMES, D. P., LEE, J. M. & TOKSÖZ, M. N. 1996. Velocity variations and water content estimated from multi-offset, ground-penetrating radar. Geophysics, 61, 683-69
PIPAN, M., FORTE, E., DAL MORO, G., SUGAN, M., GABRIELLI, P. & FINETTI, I. 2004. Multi-fold Ground Penetrating Radar Imaging and Classification of Buried Targets for Environmental Applications. Progress in Electromagnetic Research Symposium, Pisa, Italy, March 28 – 31.
REINE, C., CLARK, R. and VAN DER BAAN, M. 2012. Robust prestack Q-determination using surface seismic data: Part 1 — Method and synthetic examples. Geophysics, 77, R45–R56.
SALA, J. & LINFORD, N. Processing stepped frequency continuous wave GPR systems to obtain maximum value from archaeological data sets. Ground Penetrating Radar (GPR), 2010 13th International Conference on, 2010. IEEE, 1-6.



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