ESTIMATION OF SUBSAMPLE TIME-DELAY DIFFERENCES IN NARROW-BAND ULTRASONIC ECHOES USING THE HILBERT TRANSFORM CORRELATION

In many areas the time delay of arrival (TDOA) is desired. In the case of narrowband signals we propose a fast and simple method to estimate small time delays. This method is shown to have the same or better ac curacy as the cross correlation methods for small delays in the order of fractions of the sample interval. It is based on using the Hilbert transform in correlation between two signals and consists of only one scalar product, which makes it fast. It may also be used in applicatio ns with narrowband signals where the measurements are repeatable, such as ultrasonic imaging and nondestructive testing. In ultrasonic appli cations, due to fluctuations in the insonified media, a small random t ime shift may be present causing the signals to be misaligned in time. Averaging signals under these conditions will result in a distortion of the signal shape. We propose an averaging method to avoid this and to accomplish a higher SNR without the distortion. Simulations and exp eriments from ultrasonic applications are presented.