ASA 124th Meeting New Orleans 1992 October

1pPAa9. Filter order in maximum entropy echo identification.

Louis E. Roemer

Elec. Eng. Dept., Louisiana Tech Univ., Ruston, LA

The use of maximum entropy methods to detect ultrasonic echoes through phase information requires one to choose a filter order for signal processing. Choice of too low an order filter will cause the observer to miss multiple echoes. Choice of too high an order filter order will result in spurious echoes. Criteria for selection of filter order, based on noise power, are useful and well known. However, additional insight can be gained from observing the echo pattern as the filter order is changed. The effect of filter order selection is demonstrated for thin metal sheet targets, in which the echo return overlaps the original transmitted signal. Nonspurious echoes are shown to vary less with filter order than spurious echoes, thereby allowing identification.