Ground Penetrating Radar Detection Of Steel Bars Based On Wavelet Transform

Ground penetrating radar (GPR) is a valuable non-destructive method for detecting the steel bars in reinforced concrete structures., however, there are still many problems to be solved. How to determine the position of steel bars in deep concrete structures and how to measure the diameter of steel bars are two difficult problems. We use wavelet transform to solve the problems.In the article, the principal of the ground penestrating radar and its application in engineering is presented.We also introduce the basic theory of wavelet transform and the features of all kinds of wavelet function. The advantage of wavelet transform in handling the non-stationary signal is also pointed.We find out the effect of steel bars on GPR wave by correlation coefficient and conclude the essence of GPR scan image is utilizing the change of phase of GPR waves to indicate the position of rebar. As for the decision of the deep position of steel bars, we originate the radar images of the parameters of instantaneous amplitude, instantaneous phase, instantaneous frequency and the modulus maxims based on the wavelet transform and compare the images.The measurement of the diameter of steel bar is quite difficult and few previous experiments have been successful. We compare the difference of the continuous wavelet transform(CWT), discrete wavelet transform(DWT), stationary wavelet transform (SWT) and make the contour map of DWT and SWT cD5 coefficients, then find that SWT is effective method to measure the diameter of steel bars. We measure five steel bars and get the diameter based on SWT. The error of diameter is only 2mm. The horizontal position and depth is also obtained and the maximum error is only 4mm. After acquiring the parameters (diameter, depth, and horizontal position) of steel bars, we make 3D image. Choice of wavelet bases that can best interpret the raw GPR data is also important. There are different types of wavelet bases whose qualities vary according to several properties. By using the different wavelet function to make the contour maps of SWT coefficients, we conclude the short support width and orthogonality are the most important properties when choose the wavelet bases.The article has profound significance in the application of GPR in detection of concrete structures...