SPECKLE PHOTOGRAPHY FOR REVEALING HIDDEN STRUCTURES

1
SPECKLE PHOTOGRAPHY FOR REVEALING HIDDEN
STRUCTURES

• APRIL, 24 2007
• STEVEN MERSCH
• smersch_at_pointsource-inc.com
• POINT SOURCE, INC.
• 1864 DAYTON PIKE
• GERMANTOWN, OH 45327

2
Speckle photography / speckle interferometry
holds the potential to provide a fast, simple,
compact, portable and affordable means of
checking a surface for features potentially
hidden behind or beneath the surface.
THE CONCEPT
3
(No Transcript)
4
Requirements for performing speckle photography

• A laser (coherent) light source for subject
  illumination (see white light exception).
• A subject with a diffuse (rough) surface.
• A high resolution (electronic) camera.
• Image processor that is capable of storing a
  reference, performing image subtraction, and
  applying image smoothing algorithms.
• An energy means for introducing a disturbance
  into the subject.

5
Names of Speckle Techniques

• Laser Speckle Interferometry
• Laser Speckle Photography
• White Light Speckle Photography
• Sunlight Speckle Photography
• Electronic Speckle Pattern Interferometry (ESPI)
• Laser Speckle Contrast Imaging
• Laser Speckle Imaging (LSI)
• Laser Speckle Contrast Analysis (LASCA)
• Speckle Metrology

6
Basic Speckle Imaging System
7
Dual Illumination Interferometric Method
8
Example of speckle interferometry
Difference of the two speckle patterns
Speckle pattern of undeformed surface
Speckle pattern of deformed surface
9
Electronic Speckle Pattern Interferometry (ESPI)

• Use TV system to record speckle instead of film
• Gives real-time measurements
• Minimum speckle size limited by camera
  resolution
• Can perform computer analysis of speckle data

10
(No Transcript)
11
(No Transcript)
12
Using Laser Speckle to Image Subsurface Void
A 5mm hole covered by a sheet of white paper.
First image is an unprocessed photo. Second and
third are subtracted and processed speckle
images.
13
White Light Speckle Photography

• Has been used for studying movement or
  distortions in large areas (large subjects).
• Incoherent light source ? Lower absolute
  sensitivity.
• Can use the sun as a light source but must use a
  very high resolution camera for inspection of
  large areas and must collect images with the sun
  in nearly the same orientation (e.g. glacier
  movement study)

14
Concept for Finding Tunnels with Speckle
Photography

• Illuminate the surface to be checked with laser
  or controlled white light source.
• Image the surface with a high resolution camera.
• Store the image as the background image.
• Cause a disturbance (i.e. from a small
  underground detonation) to propagate through the
  area of interest.
• Collect images while the disturbance propagates
  through the area of interest.
• Perform image subtraction of the background
  stored image.
• Perform further smoothing of the difference
  image.
• Examine the resulting difference image for
  anomalies.
• The effect of a subsurface disturbance on the
  surface is a function of subsurface features.

15
References

• Nothdurft and Yao, Imaging Obscured Subsurface
  Inhomogeneity Using Laser Speckle, Dec, 2006,
  Vol. 13, No 25, Optics Express.
• Conley and Genin, Application of Speckle
  Metrology at a Nuclear Waste Repository, SPIE
  Vol. 1332, 1990, pg 798.
• Briers, David, Laser Speckle Contrast Imaging
  for Measuring Blood Flow, Proceedings of the
  Symposium on Photonics Technology for 7th
  Framework Program, 2006, pg 328.
• Stetson, A Review of Speckle Photography and
  Interferometry, Optical Engineering, Vol. 14,
  Sept-Oct 1975, pp 482-489.
• North, Smith and Browne, Development of Sunlight
  Speckle Photography, Proc SPIE Vol. 2921, March,
  1997, pp393-398.
• Aguanno, Lakestani, Whelan, Connelley, Speckle
  interferometry using a CMOS-DSP camera for static
  and dynamic deformation measurements, ICEM12
  12th International Conference on Experimental
  Mechanics, Sept, 2004.
• Conley and Morgan, Speckle Photography Applied
  to Measure Deformations of Very Large
  Structures, SPIE Vol. 2446, pp161-168.