Edgar Conley

A WHOLE-FIELD INTERFEROMETRIC SCHEME FOR MEASURING STRAIN AND FLOW RATES OF GLACIER AND OTHER NATURAL SURFACES

The flow of glacier ice is mapped using high-resolution photography and non-coherent-light speckle interferometry . Youngs fringe patterns result when a double-exposed photoplate image of the straining surface is illuminated by a narrow beam of coherent light. Geometry gives a relationship between the ice surface displacement vector and the interference fringe patterns. This displacement vector is corrected for rigid-body (camera) movement and projected onto the ice surface using topological maps. The strain during the time-lapse interval is thus known. Comparison with data acquired by surveying techniques at Nisqually Glacier, Washington, U.S.A., is limited because of small overlap of the surface studied. In the areas for which results can be compared, our experiments yield a flow of 0 .6 mi d where conventional methods yield about 0.4 m/ d. ZUSAMMENFASSUNG. Ein neues inlerJeromelrisches Ganzfeld-System zur Messung von Spannungs- und Fliessratell aufGlelscher- ulld anderen nalurlichen Oberfliichen. Die Fliessbewegung von Gletschereis wird durch hochaufliisende Photographie und Interferometrie mit nicht-kohiirentem Licht erfasst. Bei der Beleuchtung einer doppelt belichteten photographie der sich verformenden Oberfliiche mit einem scharf gebiindelten Strahl kohiirenten Lichtes ergeben sich Youngsche Figuren. Geometrisch lassen sich Beziehungen zwischen dem Verschiebungsvektor der Eisoberfliiche und dem entstehenden Fransenmuster herleiten . Der Verschiebungsvektor wird hinsichtlich eventueller Bewegungen eines starren Kiirpers (Kamera) korrigiert und mit Hilfe topologischer Karten auf die Gletscheroberfliiche projiziert. Die Deformation wiihrend des Zeitintervall s ist damit bekannt. Der Vergleich mit Oaten die mit konventionellen Methoden am Nisqually Glacier, Washington, U.S.A., gewonnen wurden, ist infolge der geringen Oberlappung der beiden untersuchten Oberfliichenst iicke begrenzt. Im Uberlappungsgebiet beider Methoden ergaben unsere Versuche einen Fluss von 0 ,6 m pro Tag, wiihrend die konventionelle Messung c. 0,4 m pro Tag lieferte.

Enhancing sensitivity of the white-light speckle method in terrestrial applications

Noncoherent-light speckle interferometry techniques have been used for terrestrial motion measurements. The long imaging distances typical of these applications limit sensitivity and accuracy because of atmospheric turbidity. Experiments show that the performance of camera systems used to record glacier surface speckle agrees with the predictions of theory developed for astronomical work. Several methods to enhance the technique are suggested.

Speckle-photography study of nuclear-waste vault deformations

White-light speckle photography was applied to measure the viscoplastic deformation of a proposed nuclear-waste repository. The repository vaults are carved into bedded salt deep in the earth, and deform extremely slowly. The research demonstrates the feasibility of using whole-field techniques to detect mine wall strains, confirms certain, but not all, measurements of point-by-point instruments, and also confirms the predictions of a site-specific numerical model.

Speckle photography applied to measure deformations of very large structures

Fundamental principles of mechanics have recently been brought to bear on problems concerning very large structures. Fields of study include tectonic plate motion, nuclear waste repository vault closure mechanisms, the flow of glacier and sea ice, and highway bridge damage assessment and residual life prediction. Quantitative observations, appropriate for formulating and verifying models, are still scarce however, so the need to adapt new methods of experimental mechanics is clear. Large dynamic systems often exist in environments subject to rapid change. Therefore, a simple field technique that incorporates short time scales and short gage lengths is required. Further, the measuring methods must yield displacements reliably, and under oft-times adverse field conditions. Fortunately, the advantages conferred by an experimental mechanics technique known as speckle photography nicely fulfill this rather stringent set of performance requirements. Speckle seemed to lend itself nicely to the application since it is robust and relatively inexpensive. Experiment requirements are minimal -- a camera, high resolution film, illumination, and an optically rough surface. Perhaps most important is speckles distinct advantage over point-by-point methods: It maps the two dimensional displacement vectors of the whole field of interest. And finally, given the methods high spatial resolution, relatively short observation times are necessary. In this paper we discuss speckle, two variations of which were used to gage the deformation of a reinforced concrete bridge structure subjected to bending loads. The measurement technique proved to be easily applied, and yielded the location of the neutral axis self consistently. The research demonstrates the feasibility of using whole field techniques to detect and quantify surface strains of large structures under load.

Resolution experiments using the white light speckle method

Noncoherent light speckle methods have been successfully applied to gauge the motion of glaciers and buildings. Resolution of the optical method was limited by the aberrating turbulent atmosphere through which the images were collected. Sensitivity limitations regarding this particular application of speckle interferometry are discussed and analyzed. Resolution limit experiments that were incidental to glacier flow studies are related to the basic theory of astronomical imaging. Optical resolution of the ice flow measurement technique is shown to be in substantial agreement with the sensitivity predictions of astronomy theory.

Waste-Management Education and Research Consortium (WERC) annual progress report, 1991--1992

This report contains the following appendices: Appendix A - Requirements for Undergraduate Level; Appendix B - Requirements for Graduate Level; Appendix C - Graduate Degree In Environmental Engineering; Appendix D - Non-degree Certificate Program; Appendix E - Curriculum for Associate Degree Program; Appendix F - Curriculum for NCC Program; Appendix G - Information 1991 Teleconference Series; Appendix H - Information on 1992 Teleconference Series; Appendix I - WERC interactive Television Courses; Appendix J - WERC Research Seminar Series; Appendix K - Sites for Hazardous/Radioactive Waste Management Series; Appendix L- Summary of Technology Development of the Second Year; Appendix M - List of Major Publications Resulting from WERC; Appendix N - Types of Equipment at WERC Laboratories.