Morphological Filters: Statistical Evaluation and Applications in Ultrasonic NDE

Abstract

In this paper, morphological filters [1-4] have been applied to detect flaw echoes in ultrasonic signals contaminated by grain scattering noise (i.e., clutters or speckles). In particular, the statistical properties of morphological operations (i.e., dilation, closing, clos-erosion and clos-opening) are examined using Monte Carlo simulation when applied to signals with uniform and Rayleigh distributions. The simulated results and their statistics (mean and variance) present an interpretation of the noise suppression capability of morphological filters and their biasing effects. This information has been utilized to design a suitable structuring element to enhance flaw-to-clutter ratio in ultrasonic testing. The processed experimental results (A-Scans and B-Scans) show that morphological filters can improve flaw visibility by suppressing grain scattering noise.