Velocity and density field measurements by digital speckle method

Velocity and density field measurements based on image processing of Laser speckle or pseudo-speckle pattern have been developed. Laser speckle veloci metry (LSV) or white-light speckle velocimetry (WSV), which corresponds to a high-image-density PIV, gives a local velocity vector map or whole field velocity contour map of a two-dimensional Row field seeded densely with fin e particles. This technique has an advantage in high-speed Row measurement without limit of frame rate except for directional ambiguity. New technique s of laser speckle photography and laser speckle interferometry by means of digital image processing have been developed recently for density field me asurements. In laser speckle photography. a local density gradient vector m ap is reconstructed by cross-correlation evaluation between the reference a nd the object speckle patterns. In laser speckle interferometry, an equi-de nsity contour map is reconstructed by image subtraction between the referen ce and the object interferometric speckle patterns. (C) 2001 Elsevier Scien ce Ltd. All rights reserved.