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Phase-contrast Enhancement Without Spatial Filters for Seismic Holography.

NTIS: PB 215 817 :17 pages
Future applications of seismic holography to "seismically transparent phase objects," such as rock inclusions, fracture zones, liquid-filled cavities, etc., will require techniques to improve the poor image contrast generally characteristic of these objects. Although conventional phase-contrast enhancement techniques could be used, these methods involve additional optical elements such as quarter-wave spatial filters. Owing to the anticipated practical difficulties of properly alining such optical devices and properly locating poorly defined image planes and filter planes, this approach is not considered to be well-suited to the case of seismic holograms and their laser reconstructions. Results similar to those achieved with spatial filters may be obtained without filters by specially processing the seismic hologram data. The new process, which is an extension of gabor's subtraction holography, achieves an improvement in contrast by an interferometric technique. The process involves adding a "before" hologram without an object present to a 90 deg phase-shifted "after" hologram with the object present. Then, the combination is reconstructed with a laser or by computer. Not only is the image contrast improved in such processed holograms, but the images are also phase-contoured. In general, the latter feature is not to be expected when conventional phase- contrast enhancement techniques are employed. The new technique is experimentally verfied by examining computer-generated synthetic seismic holograms rather than by examining actual seismic field data. However, resul
Publication Date
Document Type
IH; Report of Investigations
Fiscal Year
NTIS Accession No.
NTIS Price
Identifying No.
RI 7721
NIOSH Division
Source Name
NTIS: PB 215 817