Precise emissivity of rock samples

To differentiate among geological materials and vegetation using thermal infrared spectra, radiometric measurements require corrections for local temperature variations and reflected radiation. A laboratory technique is described for the determination of spectral emissivity signatures for natural geological samples using a Fourier Transform Infrared Spectrometer and the self-emission of the scene. The approach described does not require control of the sample temperature. A quantitative assessment of uncertainties is presented. Comparison of the emissivity measurements from natural geological specimens with hemispherical reflectance data gave an average difference of about 0.01 in emissivity, except near strong features of the spectra. The technique is applicable to field measurements of high-emissivity objects.