EE 275 Digital Signal Processing

“X” MARKS THE SPOTMohamed Metwally Advisor: Professor Mirchandani

EE 275 Digital Signal Processing

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 1Channel 2

Pulse repetition is 34KHz

EE 275 Digital Signal Processing

Data Collected – Rebar in Air B-Scan

Raw data of the channel 2

Raw data Processed data

EE 275 Digital Signal Processing

Data Collected – Rebar in Sand B-Scan

Raw data of the channel 1

Raw data Processed data

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.