WAVELENGTH CALIBRATION OF ARRAY SPECTRORADIOMETERS

The wavelength calibration of an array spectroradiometer is essential to its use. In principle, the wavelength scale can be related to array pixel positions using simple formulae but in practice this is hardly ever done. More commonly, a polynomial or other functional fit is made based on measurements of gas-discharge lamps, lasers or suitable absorptive materials. The expected smooth relationship between wavelength and pixel position is generally not perfect and explanations for differences are rare. Some explanations are offered here with discussions on their impact. Assignment of "known" wavelengths to measured lines can be difficult a priori. Focus and aberration changes with wavelength can distort peak shapes and refraction through windows and filters can move peaks. Rapid responsivity changes and etaloning can also move peaks to higher or lower wavelength. The combined effect of these may be sufficient to account for deviations from the expected smooth relationship.