Wavelet-based estimator versus spectral correlation method for acoustic target sizing

Abstract

This paper presents two different methods for estimating the diameter of an immersed wire insonified by an ultrasonic plane wave. The first part of the backscattered echo, called the quasi-rigid backscattered echo (QRBE), and the quasi-rigid form function (QRFF) are described first. It is shown that the QRBE contains the size information (diameter) of the target. In the first method, this size is obtained by associating a pattern recognition procedure with a spectral correlation. The second method is based on a continuous wavelet analysis of the QRBE at a particular scale with a judiciously selected wavelet. After a brief description of the wavelet tool, we present in detail the wavelet-based approach for target sizing. Results thus obtained are compared with experimental measurements using copper and steel wires. They show that for the largest diameters, the results are similar. On the other hand, the more the diameter decreases, the more the wavelet-based estimator is distinguished by giving a better relative precision. In terms of the cost of calculation, the second method is better since it requires only one wavelet transform at only one single scale against a Fourier transform and an iterative correlation procedure, necessary in the first technique.