Development of sunlight speckle photography

Heather C. North; E. W. Smith; Roger F. Browne

doi:10.1117/12.269849

20 March 1997 Development of sunlight speckle photography

Heather C. North, E. W. Smith, Roger F. Browne

Proceedings Volume 2921, International Conference on Experimental Mechanics: Advances and Applications; (1997) https://doi.org/10.1117/12.269849
Event: International Conference on Experimental Mechanics: Advances and Applications, 1996, Singapore, Singapore

Abstract

A speckle technique is being developed for full-field displacement analysis of large structures illuminated by sunlight. Potential applications include displacement measurement of civil engineering and geological bodies. A particularly challenging and interesting application is the study of rock debris-covered glaciers where the surface offers an excellent natural speckle pattern. The large object distances involved in the study of glaciers (up to 6 km) introduce questions regarding atmospheric effects, lens aberrations and resolution, speckle generation and the suitability of sunlight as an illumination source. This paper describes a study of the feasibility of speckle photography in the presence of these factors. It then presents quantitative results illustrating the effect these factors have on the sensitivity and accuracy of the method. In particular we consider; (1) The spatial frequency content of an incoherent speckle image is dependent on the filtering of object spatial frequencies by a transfer function formed from the combined imaging properties of the lens and the atmosphere. Experimental results characterizing the effects of atmosphere on imaging quality are presented; (2) A unique speckle pattern is generated by a certain illumination angle so daily speckle photographs of the glacier surface are taken at a similar time. We consider how much tolerance the technique has to variation in sun angle.

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Heather C. North, E. W. Smith, and Roger F. Browne "Development of sunlight speckle photography", Proc. SPIE 2921, International Conference on Experimental Mechanics: Advances and Applications, (20 March 1997); https://doi.org/10.1117/12.269849

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