Filtering some types of fringe patterns in the spatial frequency domain enables to reconstruct a complex number distribution containing full information about the phase of the analyzed pattern. It is shown that by registering two images mutually shifted in phase by (pi) it is possible to reduce errors introduced by the filtering process mentioned above. The technique of further correction of the intrinsic phase error caused by filtering using the Hilbert transform has been recently proposed for patterns with spatial carrier frequencies in Cartesian coordinates. In this work we show that the same approach can be applied to analyze fringe patterns with radial carrier frequency (in polar coordinates). The method of efficient filtering of such patterns and the technique for correcting the intrinsic error caused by the Hilbert transform are given. The final accuracy of the presented HT-based method is very close to the one which can be obtained by applying the phase stepping method.
A fiber optic sensor prototype to detect nitride and nitrate in water is presented. Its working principle is based on a spectrophotometric technique, and makes use of specific chemical reagents.
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