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Combining Laser Measurements With Backward Wave Techniques for Evaluation of Underground Openings.

Fitzpatrick GL; Skaugset RL; Davis TJ
NTIS: PB 88-235080 :48 pages
A portable optical instrument for performing multispot laser vibrometry is described. The instrument is capable of measuring arrival times, surface motion frequency, and surface velocity and displaying these quantities in various useful ways. Sigma research is currently pursuing the development of such optical measuring systems for the evaluation of structures in rock by noncontact interferometry methods. The goal of the work was to develop a portable tripod mounted measuring system which can be set up at arbitrary distances (up to 30 m) from a surface and project four in- line laser sample beams on this surface. A light-receiving telescope gathers the scattered light from these four spots, and provisions are made to mix this light with a reference beam from the laser. Four photodiodes are employed to determine the resultant interference signals which characterize the motion (particle velocity, frequency, amplitude) of the four illuminated spots on the surface under study. Information of this type can then be used to characterize the elastic or mechanical properties of the surface in question. In some cases (if more than four spots are involved) this surface information could be back-propagated to draw inferences about the internal state of the material volume bounded by this surface.
Publication Date
Document Type
CP; Final Contract Report;
Fiscal Year
NTIS Accession No.
NTIS Price
Identifying No.
OFR 46-88
Source Name
NTIS: PB 88-235080
Performing Organization
Sigma Technologies
Page last reviewed: November 19, 2021
Content source: National Institute for Occupational Safety and Health Education and Information Division