[Extracting projections from laser moire interference spectra]

Laser Moire Interference spectra of rocket exhausted plumes were analyzed. Projections for reconstruction were figured out, and air density distribution was reconstructed. Moire deflectograms of the plumes were produced and captured with a home-made, wide-range, high-sensitivity Moire deflectometer. Moire interference spectra were processed by phase unwrapping technique with Fourier transform, so the space phase distribution of Moire deflectograms was extracted. The background was worked out based on the margin of the Moire deflectograms, and so was the space phase distribution of the background. The phase shift distribution of distorted Moire interference spectra could easily be obtained by calculating the difference between the two space phase distributions. The relative projections could be extracted from the phase shift distribution. The air density distribution of the plumes was calculated by simple self-correlative algebraic reconstruction technique (SSART) based on deflected angles for projections. Eight projections with equal direction interval of 20 degree were used for reconstructing the air density distribution of a plume section. As a result, with phase unwrapping technique based on Fourier transform, any cross section projection could conveniently be worked out from the Moire deflectogram of rocket exhausted plumes. The air density distribution of the cross section could be reconstructed by SSART. So, SSART with deflected angle for projection is a kind of super nonlinear deflection tomography.