On the use of the non-stationarity of the structural noise for defect visibility enhnacement in ultrasonic inspections

Abstract

Structural noise is an important distortion source in ultrasonic images of highly dispersive materials. This noise can considerably mask the flaw signals and cannot be eliminated using standard techniques for noise cancelling like band-pass filtering or temporal averaging. Fortunately, this noise has several characteristics that may help an algorithm designer to develop methods that improve the defect visibility.

In the literature there exist many techniques for flaw visibility enhancement in the presence of structural noise. However, many of the proposed algorithms do not systematic exploit the above mentioned characteristics. In this work we analyze the structural noise from a point of view of an algorithm developer that seeks parameters that may help to eliminate the noise enhancing the defect visibility. Also, we present several algorithms examples that, using this information, dramatically improve the visibility of the flaw echoes.