SUPERRESOLUTION METHODS APPLIED TO THE FINE-STRUCTURE OF ULTRASONIC PULSES SCATTERED BY A VERTICAL SUBSURFACE HANGING CRACK

A superresolution method is applied to the analysis of ultrasonic sign als reflected from a vertical subsurface crack which scatters and tran sforms a transverse wave. The pulse length is reduced by extrapolating the spectra, which enables one to observe echo signals related to the wave type transformation at a crack having a length of several wavele ngths. The fine structure of the pulse can be considered as a classifi cation feature. Images are presented of cracks obtained by coherent me thods from ordinary echo signals and one having extrapolated spectra.