Optimal Incident Angles in Scanning Tomographic Microscopy
The scanning tomographic acoustic microscope utilizes principles of digital tomography to obtain high-resolution subsurface imaging. An algorithm based on back-and-forth propagation is employed to reconstruct the tomograms. We have shown that the expected mean-squares error is a minimum and the source matrix is simply the identity matrix if the object is illuminated from certain optimal incident angles.
In usual practice, however, the object is insonified from angles separated from each other by a fixed interval thus giving a uniform angular spacing. The source matrix in this case is no longer the identity matrix as for the optimal case. This paper presents a quantitative analysis of the degradation of the image caused by using uniformly-spaced incident angles. We introduce a term we call “normalized error” and we one-dimensional image the asymptote for the least upper bound of the normalized error as the number of pixels goes to infinity is π/2–1 or 0.5708.
KeywordsIncident Angle Acoustical Image Image Degradation Acoustic Microscope Uniform Scheme
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