Abstract: A method of calibrating a hyperspectral imaging spectrometer. A PTFE panel (26) having substantially 100% reflectance across a spectrum of interest is mechanically inserted into the spectrometer's field-of-view. The panel (26) is illuminated by a lamp (22, 24), such as a quartz Tungsten Halogen lamp, so that reflected radiation from the panel (26) floods the spectrometer's FOV. The image generated by the spectrometer is electronically stored. Next, the reflectance panel (26) is removed and replaced with a PTFE panel (40) that is doped with a rare earth element, such as holmium oxide, dysprosium oxide, erbium oxide or other dopants. The dopant serves the purpose of producing many distinct absorption features in the reflected spectra whose wavelengths spacings and absorption line widths are precisely known. The image obtained form the doped PTFE panel (40) is then electronically stored.