Measurement of three-dimensional density distributions in a transient unstable stratified flow is important for the safety analysis on the advanced type nuclear power plant. Three-dimensional density distribution can be reconstructed using computer tomography technique from interferogram images. However, in the experiment, only a few interferogram images could be taken. Conventional tomography techniques have low accuracy with the limited interferogram images, since the information of the projection is not enough for the reconstruction.

While, the transient interferogram images can be easily taken using the real-time holographic interferometer and/or Mach-Zehnder interferometer. That is, there are enough information for the temporal domain. In this study, a transient three-dimensional (4D) reconstruction technique was proposed. The four-dimensional density distribution was assumed to be expressed as the summation of Elementary Distribution Functions (EDFs). The EDFs were distributed not only in the spatial domain, but also in the temporal domain. The tomography was carried out as the optimization of the arrangement for EDFs, using the temporal projection information.

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