METHOD OF CALCULATING THE MINIMUM TEMPERATURE DIFFERENCE PERCEIVED OF UNDERSAMPLED THERMAL IMAGERS
Keywords:Minimum temperature difference perceived, Nyquist frequency
Background. Nowadays thermal matrix detectors are commonly used. A common feature of these thermal imagers is the opportunity to sample the signal in two directions, horizontal and vertical. The sampling theorem deals with the capacity of a sampled system to transmit information. In case of optical information this capacity means the ability of the system to reproduce the spatial frequencies that form a particular scene. The principal result of this theorem is to establish an upper limit for frequencies that can be accurately transmitted and reconstructed from the original signal. If the spectrum of the original signal contains frequencies higher than the Nyquist frequency, the original spectrum and the replicated spectra overlap. In such a case, the original signal can by no means be reconstructed. An imager that can overlap the original spectrum with the back-folded spectrum is called undersampled. The imager is undersampled if the MTF prefilter is not equal to zero at Nyquist frequency.
Objective. The aim of the paper is to study the method of calculating the minimum temperature difference perceived, which will help determine the resolution of the thermal imager outside the Nyquist frequency.
Methods. New concept of the minimum temperature difference perceived is determined based on the concept of minimum resolution temperature difference that helps fulfill the objective.
Results. A graph of the function of the minimum temperature difference perceived is obtained, which allows determining the resolution of the thermal imager outside the Nyquist frequency.Conclusions. The developed method for calculating the minimum temperature difference perceived allows us to construct a graph of this function. The graph in turn shows that there is a real possibility to determine the resolution of the thermal imager outside the Nyquist frequency, at a higher value of the temperature contrast of the Foucault measure.
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