Temporal and spatial spectral features of B-scan images

B-scan images of metals are frequently used in ultrasonic nondestructive evaluation for flaw detection purposes. Often, the backscattered grain noise masks the flaw echo, making it difficult to visually distinguish the flaw signal from the grain echoes. Previously, spatial and frequency compounding, as well as decorrelation techniques have been used to enhance the flaw echo. The partial spectra, i.e., the temporal or spatial frequency components of the B-scan image, are used individually to obtain information regarding the flaw location. It is observed that the partial spectra behave in a distinct manner when the B-scan contains a flaw, and provide more insight than the conventional two-dimensional spectrum. Using this information, a two-dimensional filter that significantly suppresses grain noise can be designed. Experimental results using data from stainless steel samples are presented