Method for determining a correction value function and method for generating a frequency-corrected hyperspectral image

A method for generating a frequency-corrected hyperspectral image of a sample with a Fourier Transform infrared (FTIR) measurement arrangement including an infrared detector having a plurality of sensor elements, the method comprising, for each of the plurality of sensor elements which are respectively located at a position (x,y) of the IR detector:

• recording an interferogram IFGPxy with an equidistant sampling grid axy with the sensor element;
• Fourier transforming the interferogram IFGPxy, to determine a spectrum Sxy(ν) with a frequency axis;
• wherein the spectrum Sxy(ν) for each of the plurality of sensor elements is corrected with a correcting quantity function kF(x,y) for calibrating the FTIR measurement arrangement with the IR detector,
• wherein the correcting quantity function kF(x,y) is determined with a method which comprises:
• a) recording interferograms IFGRxy of a reference sample with the plurality of sensor elements of the IR detector;
• b) calculating spectra R of the reference sample by Fourier transforming the interferograms IFGRxy of the reference sample for at least four sensor elements;
• c) calculating correcting quantities kxy by comparing each spectrum of the spectra Rxy of the reference sample calculated in said step b) with a reference data set of the reference sample, wherein the reference data set comprises a target position ν1 of a selected absorption peak P of the reference sample;
• d) determining the correcting quantity function kF(x, y) based on the correcting quantities kxy calculated in said step c),
• wherein the correcting quantity function kF(x,y) is determined by stretching or compressing the spectra Rxy of the reference sample calculated in said step b), or by dividing the target position vL and an actual position νxy, wherein the interferogram IFGPxy is recorded with the equidistant sampling grid axy=a0/kF(x, y) and wherein spectra of the sample are subsequently generated by a Fourier transform of corrected interferograms, where a0 provides a value for the equidistant sampling grid axy when calculating values for the frequency axis.