The determination of surface topology by the signal processing of ultrasonic pulses

The authors present results from the processing of data obtained from the reflection of broadbeam ultrasonic pulses from a selection of surfaces. The main aim is to produce height distribution curves of these surfaces. Surfaces tested include specially designed grooved surfaces, a paint layer and a hidden stepped surface. The effects of tilt are also investigated. Two signal processing methods are compared: the maximum entropy method and the Wiener-Hopf filter. It is demonstrated that maximum entropy produces not only more visually pleasing output, but also output that shows very close correspondence with the desired result. Comparison with a conventional stylus instrument is provided, and although resolution capabilities are different, a method of comparison is given. Future aims and problems to be overcome in producing a practical instrument are discussed.