Abstract
This paper discusses a feedback iteration technique that provides the enhancement of backward reconstruction in acoustical imaging. Reconstruction of a vibrating surface motion from acoustic holographic data causes computational difficulties because the problem is ill posed. In order to deal with these difficulties, a method is developed based on a recursive algorithm, where the inverse problem is converted to a well-posed forward propagation problem. An initial guess regarding the source images is required to activate the iterative inversion method. Then, the tentative image is propagated forward to the hologram plane and the residue is determined. Next, a feedback operator is used to process the residue by which the image is updated. Two types of feedback operators were investigated: (1) a Wiener suboptimal operator, and (2) a dynamic, optimal operator (designed subject to minimum mean-square-error optimization criteria). The performance of these iteration methods was investigated by numerical simulations of the holographic reconstruction of a baffled piston field. Both iteration methods provided satisfactory convergence and were found to be relatively insensitive to the choice of initial guess and noise parameters used in the feedback operators. © 1995, Acoustical Society of America. All rights reserved.