| 摘要 |
A Holographic Diffraction Image Velocimetry (HDIV) providing the three-dimensional (3-D), three-component (3-C) detection of velocity or displacement field. The HDIV technique and system are based on the independent reconstruction of time-sequence scenes captured on a single recording plate by dual-reference-beam, off-axis holography. The local areas of individual images, without any specific-particle focusing, are then scanned section by section with a solid state camera to obtain sufficient readout resolution. For velocity extraction, the image section that best correlates to the original image in a plane window is computationally searched from a transplaced volume window in the displaced field. Initially, in-plane motion is found statistically by applying two-dimensional cross-correlation (CC) to the middle section of the volume window, obtained with an intermediate depth of focus of the imaging system. Out-of-plane displacement is then located by cross-product, that is, by directly comparing the original image section with the sections along the optical axis at the in-plane displacement position, with a short depth of focus. The HDIV technique allows experimental freedom and post-control in data acquisition with reconstructed images. It can cover an extended region with high resolution and accuracy through utilization of high-density fine seed-particles. Its computation processing can further enhance performances without velocity sign ambiguity.
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