Optical EngineeringImprovement of a series expansion approach to interferometric tomography via natural pixel decomposition
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Interferometric reconstruction of three-dimensional flow fields, that is, interferometric tomography, can be a very useful diagnostic tool. It is noninvasive and can capture gross fields; however, it frequently confronts a challenging problem of reconstructing fields from insufficient data. In most cases, flow-field interferometric data are sparse, nonuniform, noisy, and incomplete in projection and scanning because of opaque objects present either inside or outside the field. Recently, a new method has been developed in an effort to improve reconstruction under these ill-posed conditions. The method is appropriate for reconstructing flow fields with the distinct data characteristics, being based on natural pixel decomposition of the field. It employs rectangular grid elements of different sizes and aspect ratios. It thus reflects intrinsic spatial resolution information contained in the data and allows better resolution and accuracy in the region with more probing rays. Computer simulation of experiments has demonstrated superiority of the method to the conventional one. In simulation, the temperature field of a gravity-driven flow of two interacting heat sources, produced by a numerical code, are tested. Both the maximum and average reconstruction errors are reduced appreciably. Especially, the reconstruction demonstrates substantial improvement in the region with dense scanning by probing rays.