Selecting parameters of digital filters during spectrophotometric research

In various fields of knowledge when studying changing processes, the response received by a physical instrument allows to nominally divide the analyzed signal into two components: “useful” signal and “disturbances” signal. In particular, while solving tasks on qualitative and quantitative spectrophotometric analysis there occur problems with distortion of absorption bands by disturbances of various natures: presence of uncompensated atmosphere absorption spectra, influence of spectra of molecules adsorbed on a sample’s surface, presence of interference noise in thin and multi-layer objects.
This paper provides a comparative analysis of the influence of filtration of model absorption spectrum by median filter and Savitzky–Golay filters of zero-first order (SG0), second-third order (SG2), and fourth-fifth order (SG4). The model spectrum was described by Gauss and Lorentz absorption contours. Based on the results of the numerical experiment recommendations are given on optimal filtration of experimental absorption spectra of condensed mediums for their further analysis and processing:

• for complete suppression of “disturbances” absorption bands the use of median filter is preferable, while for Gauss contour the filter bandwidth should be 5 times bigger than the full width at the half height of the suppressed absorption band, and for Lorentz contour this ratio should exceed 20;
• changing of the relative intensity of the “useful” signal absorption band by less than 1 % is fulfilled at a certain relative bandwidth. In case of Gauss absorption band the relative bandwidth for median filter should not exceed 0,2, for filters SG0 — 0,2, SG2 — 0,9, SG4 — 1,6. For Lorentz contour this ratio should for median filter not exceed 0,2, for filters SG0 — 0,2, SG2 — 0,7, SG4 — 1,1.