X marks the spot
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“X” Marks the spot. Mohamed Metwally Advisor: Professor Mirchandani. Conceptual Background. Radar is used to obtain object information by measuring the characteristics of the electromagnetic (EM) fields scattered by the object

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“X” Marks the spot

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EE 275 Digital Signal Processing

“X” Marks the spot

Mohamed MetwallyAdvisor: Professor Mirchandani


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


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


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


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


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


Set Up

EE 275 Digital Signal Processing


Set Up

Channel 1

Channel 2

Pulse repetition is 34KHz

EE 275 Digital Signal Processing


Data Collected – Rebar in Air B-Scan

Processed data

Raw data

Raw data of the channel 2

EE 275 Digital Signal Processing


Data Collected – Rebar in Sand B-Scan

Raw data

Processed data

Raw data of the channel 1

EE 275 Digital Signal Processing


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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