Signal-to-noise ratio enhancement based on the whitening transformation of colored structural noise

In the ultrasonic testing and evaluation of highly scattering materials (i.e. non-homogeneous media such as composites, layered and clad materials) structural noise is an important limitation to the visibility of flaw echoes. This noise cannot be reduced by conventional linear filtering or by time-averaging techniques. In order to enhance the defect-to-background noise ratio (SNR), many different algorithms have been developed over the years. This work analyzes three new strategies for SNR enhancement based on the whitening transformation of the colored structural noise. By using this transformation, the small spectral differences between noise and flaw echoes are exploited, thereby allowing an improvement in the visibility of the flaw.