This paper presents a method to measure three-dimensional gas temperature distribution without inserting a
probe into the gas using techniques of computed tomography and optical interferometry. The temperature
distribution can be reconstructed from a set of two-dimensional optical difference images for which the incident
angle of each distribution differs. The each optical difference is measured by an interferometer with four mirrors
which are movable and rotatable to control the incident angle. The temperature measurement system has two
kinds of errors. The first is the error in the reconstruction caused by the limited angle of projection; the direction
of the incident angle is limited in a certain region because of the limited arrangements of mirrors. The second
is the errors in an evaluation of the projection data which is the two-dimensional optical difference distribution,
which are included in steps to evaluate the optical difference; a carrier frequency detection of background fringe,
a carrier component filtering, phase unwrapping, and so on. This paper shows improvements of accuracy of the
reconstruction by adding a certain projection data to the original data set, and also the improvements of the
evaluation of the optical difference by using newly developed algorithms to evaluate the optical differences.
The growing interest in the applications of digital holography interferometry has led to an increasing demand for reliable phase unwrapping techniques. In digital holography, the phase carries three-dimensional surface information about the object. However, phase mapping is ambiguous as the extracted phase is returned in a form that suffers from 2π phase jumps. Furthermore, the presence of noise in the measured data, in which many singular points (SP) are found, often makes general phase unwrapping algorithms fail to produce accurate unwrapped results. Therefore, it is necessary to use a powerful phase unwrapping method to recover the desired smooth phase surface. For this reason, we developed a phase unwrapping algorithm that is applicable to digital hologram maps. The developed algorithm solves the singularity problem caused by SPs as a result of compensating its effect by using rotational and direct compensators. We show a difference in performance between our developed phase unwrapping algorithm and other well known phase unwrapping methods for digital holographic data. In addition, the methods to extract phase information of the object from hologram maps are also investigated. Results show that the developed algorithm gives satisfactory unwrapped results with low computational time cost.
In digital holography, phases carry the 3D information of objects. However, phase mapping is ambiguous, as
the extracted phase turns into a form that suffers from 2π phase jumps. In this case the phase data must be
unwrapped to fit for use. For this reason, we developed a new phase unwrapping algorithm that is applicable to
digital hologram maps. The proposed algorithm has been evaluated and compared with past phase unwrapping
methods by using simulated and real phase data. Results show that the proposed method gives satisfactory
unwrapped results with low computation time.
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