ANALYSIS OF ORDER STATISTIC FILTERS APPLIED TO ULTRASONIC FLAW DETECTION USING SPLIT-SPECTRUM PROCESSING

Split-spectrum processing of broadband ultrasonic signals coupled with order statistic filtering has proven to be effective in improving the flaw-to-clutter ratio of backscattered signals. It has been shown that an optimal rank can be obtained with a prior knowledge of flaw-to-clutter ratio and the underlying distributions. The order statistic filter performs well where the flaw and clutter echoes have good statistical separation in a given quantile region representing a particular rank (e.g., minimum, median, maximum). Order statistic filters are analyzed for the situation in which the observations do not contain equivalent statistical information. Through simulation and experimental studies applied to ultrasonic flaw detection, the robustness of order statistic filters is evaluated.