The Effects of Scanning Position and Motion Errors on Hologram Resolution

Abstract

This paper presents the results of an evaluation of image defects caused by transducer and object position and motion errors in generating an acoustical hologram. The image parameters we studied were lateral and longitudinal resolution. An error analysis, assuming slowly varying gaussian statistics, was used to estimate the mean and standard deviation. The results show that two types of errors must be considered; i.e., position errors may approach an appreciable fraction of the hologram resolution limits; however, motion errors (especially longitudinal motion) are more restrictive and appear to be limited by coherence between object and reference signals. Daubin¹ has previously noted longitudinal motion restrictions.

A limited experimental program was followed to validate the theoretical conclusions. The procedure used was to increment transducer and object errors as the hologram was generated. We found that the theoretical predictions were borne out, at least on a subjective basis. Incremental longitudinal position errors as large as 75 wavelengths caused little visible image defects while longitudinal motion errors of one-half wavelength per scan line completely destroyed the image.