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Advanced Ground Penetrating Radar (GPR) Techniques for Structural Analysis

This study explores the application of Ground Penetrating Radar (GPR) in assessing structural conditions and fault analysis. It emphasizes the importance of digital signal processing techniques, particularly the Short-Time Fourier Transform (STFT), to analyze the frequency spectrum changes of electromagnetic fields scattered by objects. By utilizing A-Scans and B-Scans in GPR data collection, this work demonstrates effective methodologies for imaging and quantifying rebar structures in various environments, ultimately contributing to advancements in engineering and construction practices.

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Advanced Ground Penetrating Radar (GPR) Techniques for Structural Analysis

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  1. EE 275 Digital Signal Processing “X” Marks the spot Mohamed Metwally Advisor: Professor Mirchandani

  2. Conceptual Background • Radar is used to obtain object information by measuring the characteristics of the electromagnetic (EM) fields scattered by the object • Ground penetrating radar (GPR) provides an effective, fast and continuous way to assess structure condition and fault analysis in different applications EE 275 Digital Signal Processing

  3. Signal Processing • Fourier analysis is only suitable for stationary signals whose properties, such as frequency response, do not change with time • The short-time Fourier transform (STFT) technique can be used to overcome the limitation of Fourier analysis and effectively track the frequency spectrum change with time (Oppenheim et al. 2005) EE 275 Digital Signal Processing

  4. Signal Processing (continued) • The information obtained from scans is run through the STFT • The information of frequency spectrum change with depth can be obtained by the above equation; • X = reflected signal; t = time variable; Ω = radial frequency; and w = window sequence EE 275 Digital Signal Processing

  5. Signal Processing (continued) • A hamming window sequence is used to extract the local frequency spectrum (Enochson and Otnes 1968) • The choice of window length is a trade-off between frequency resolution and time resolution Cited from Journal of Transportation Engineering @ASCE/April 2010 EE 275 Digital Signal Processing

  6. Practical Application – Metal Rebar • In this case, the “X” describes stay-in-place steel forms that are combined with concrete, i.e. rebar, during construction • Utilizing A-Scans and B-Scans to form a matrix of data comprising of time and voltage values • Averaging the A-Scans to create a more accurate, less noisy B-Scan image EE 275 Digital Signal Processing

  7. Set Up EE 275 Digital Signal Processing

  8. Set Up Channel 1 Channel 2 Pulse repetition is 34KHz EE 275 Digital Signal Processing

  9. Data Collected – Rebar in Air B-Scan Processed data Raw data Raw data of the channel 2 EE 275 Digital Signal Processing

  10. Data Collected – Rebar in Sand B-Scan Raw data Processed data Raw data of the channel 1 EE 275 Digital Signal Processing

  11. Bibiliography • Oppenheim, A. V., Schafer, R. W., and Buck, J. R. 2005. Discrete-time signal processing, Prentice-Hall, Upper Saddle River, N.J. • Enochson, L. D., and Otnes, R. K. 1968. Programming and analysis for digital time series data, U.S. Dept. of Defense, Shock and Vibration Info. Center. EE 275 Digital Signal Processing

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