Estimating Probability of Detection for Subsurface Ultrasonic Inspection

Acquisition of empirical Probability of Detection (POD) data involves use of controlled samples of material containing discontinuities of known characteristics, such as size, orientation, etc. For subsurface inspection, developing such a data base presents difficulties in obtaining or producing samples covering the full range of possible characteristics, and in adequately identifying those characteristics with a “referee” technique. In this paper, a method is described whereby estimates for the POD of subsurface discontinuities have been derived from a simple algorithm linking metallographic and ultrasonic measurements on a relatively small number of artificial and natural reflectors. Originally introduced solely to meet a need for mean POD, subsequent development has allowed adding confidence levels to the analysis; use of a closely related technique for providing probabilistic estimates of the size of individual discontinuities will also be described