A modified Hough transform for removal of direct and reflected surface waves from B-scans

Time of flight diffraction (ToFD) B-scans may contain horizontal lines from surface waves propagating directly from emitter to receiver and angled lines after a reflection off a surface edge. A Hough transform (HT) can detect lines but assumes lines at less than 45° from the vertical consist of a series of connected vertical segments (“thick” lines). In a B-scan image, narrow (temporally sharp) lines at less than 45° from the vertical become “sparse” such that there are gaps in the times of arrival between scan positions. This paper describes a modified HT, used to successfully identify and remove such lines from B-scans.