Target sizing: spectral method versus wavelet-based estimator

The problems tackled in this article are those of the sizing characterization of an immersed target. This wire target is insonified by an ultrasonic broadband transducer, and our goal is to compare the diameter estimation by two different methods which both rely on the analysis of the backscattered echo. It is shown that the first part of the backscattered echo (QRBE) contains the size information (diameter) of the target. The first method of radius estimation is based on the identification of the optimal parameter which ensures the best superimposition of the spectral backscattered echo segment on the quasi-rigid form function (QRFF). The second technique relies on a family of synthetic echoes obtained from the resonant scattering theory (RST). Those are analyzed by a wavelet transform of which the coefficients are used to establish a model identifying the experimental signals. Results obtained with copper and steel wires (with wires ranging from 0.25 mm to 1 mm) are compared with experimental measurements. For the two methods, the results are similar for the largest diameters. But the more the diameter decreases, the more the wavelet-based estimator is distinguished by giving a better relative accuracy.