1. “X” MARKS THE SPOT Mohamed MetwallyAdvisor: Professor Mirchandani EE 275 Digital Signal Processing

2. Conceptual Background EE 275 Digital Signal Processing  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

3. Signal Processing EE 275 Digital 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)

4. Signal Processing (continued) EE 275 Digital Signal Processing  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

5. Signal Processing (continued) EE 275 Digital Signal Processing  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

6. Practical Application – Metal Rebar EE 275 Digital Signal Processing  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

7. Set Up EE 275 Digital Signal Processing

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

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

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

11. Bibiliography EE 275 Digital Signal Processing  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.