Experiments in Fluids

, Volume 17, Issue 5, pp 315–322 | Cite as

Multi-level convolution filtering technique for digital laser-speckle-velocimetry

  • Th. Kemmerich
  • H. J. Rath
Article

Abstract

A new evaluation method for velocity measurements using digitized, single exposed speckle images is presented. The method is based on a convolution filtering technique used on different levels. Beginning with the computation of a small number of velocity vectors on the coarsest level, the solution is determined step by step on the finer levels, and the number of points is squared from one level to the next. On the coarsest level the vectors are computed with high accuracy, and good approximation is obtained through interpolation of the solution on the next, finer level. Preprocessing of the images considerably improves the accuracy and evaluation speed of the measurement. The computation of the displacement vectors on the finest level without interpolation shows that the number of erroneous vectors computed during the binarization of the images can be reduced by up to 70%. Using the convolution filtering technique on three levels allows for a further reduction of erroneous vectors by up to 40%. Use of smaller kernels and reduction of the kernel and the image area after every interpolation step reduces the computation time for a velocity vector field to 50% compared to the one-level algorithm.

Keywords

Computation Time Convolution Vector Field Velocity Vector Evaluation Method 

List of symbols

A

image area of the convolution

K

kernel of the convolution

O

overlapping area

Pc

number of multiplications and additions necessary for the computation of a velocity vector

R

correlation coefficient

Sc

size of the field of the correlation coefficients

SA

size of the image area for the convolution

SK

size of the kernel

c

column index

d

displacement of the speckles

i, j

index of the kernel

ni

number of points of gridi

r

row index

t

time of capture of the first speckle-image

Δt

time difference between the capture of the two speckle-images

ΔT

temperature difference in the thermocapillary convection experiment

z

distance of the gridpoints

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

References

  1. Adrian RJ (1984) Scattering particle characteristics and their effect on pulsed laser measurements 0f fluid flow: speckle velocimetry vs particle image velocimetry Appl Opt 23: 1690–1691Google Scholar
  2. Adrian RJ (1991) Particle-Imaging techniques for experimental fluid mechanics, Ann Rev Fluid Mech 23: 261 304Google Scholar
  3. Arnold W; Hinsch KD; Mach D (1986) Turbulence level measurement by speckle velocimetry. Appl Opt 25: 330–331Google Scholar
  4. Barker DB; Fourney ME (1977) Measuring fluid velocities with speckle patterns, Opt Lett. 1: 135–137Google Scholar
  5. Cenedese A; Paglialunga A (1990) Digital direct analysis of a multi-exposed photograph in PIV. Exp Fluids 8: 273–280Google Scholar
  6. Cho Y-C (1989) Digital image velocimetry. Appl Opt 28: 740–747Google Scholar
  7. Dudderar TD; Simpkins PG (1977) Laser Speckle Photography in a fluid medium. Nature 270: 45–47Google Scholar
  8. Ennos AE (1975) Speckle Interferometry. In: Laser Speckle and related Phenomena, Ed. Dainty JC, Springer Verlag Berlin, p. 203–245Google Scholar
  9. Grant I; Liu A (1989) Method for the efficient incoherent analysis of particle image velocimetry images, Appl Opt 28: 1745–1748Google Scholar
  10. Grant I; Qui JH (1990) Digital convolution filtering techniques on an array processor for particle image velocimetry. Appl Opt 29: 4327–4329Google Scholar
  11. Jähne B (1989) Digitale Bildverarbeitung, p 241–247, Springer Verlag BerlinGoogle Scholar
  12. Keane RD; Adrian RJ; Ford DK (1990) Single exposure double frame image velocimetry, ICALEO `90, Optical Methods in Flow and Particle Diagnostics, SPIE Vol 1602Google Scholar
  13. Merzkirch W (1990) Laser-Speckle-Velocimetry. In: Lasermethoden in der Strömungsmeßtechnik (Ed.: Ruck B) Stuttgart: AT-Fachverlag, P 71–97Google Scholar
  14. Pratt WK (1991) Digital Image Processing, pp 6, John Wiley & Sons, Inc, New YorkGoogle Scholar
  15. Ruck B (1990) Laserlichtschnittverfahren und digitale Videobildverarbetung. In: Lasermethoden in der Strömungsmeßtechnik (Ed.: Ruck B), Stuttgart AT-Fachverlag, p 367–402Google Scholar
  16. Saß V (1993) Drei-dimensionale Simulation thermokapillarer Konvektion in kubischen Behältern mittels Multi-Grid Verfahren. Dissertation, Universität BremenGoogle Scholar
  17. Schmidt M; Löffler F (1993) Experimental investigation on two-phase flow past a sphere using digital particle-image-velocimetry, Exp Fluids 14: 296–304Google Scholar
  18. Wernet MP; Edwards RV (1990) New space domain processing technique for pulsed laser velocimetry. Appl Opt 29: 3399–3417Google Scholar
  19. Willert CE; Gharib M (1991) Digital particle image velocimetry, Exp Fluids 10: 181–193Google Scholar

Copyright information

© Springer-Verlag 1994

Authors and Affiliations

  • Th. Kemmerich
    • 1
  • H. J. Rath
    • 1
  1. 1.Center of Applied Space Technology and MicrogravityUniversity of BremenBremenGermany

Personalised recommendations