Remote sensing infrared spectroscopy is the principal field of investigation for planetary surfaces composition. Past, present and future missions to the solar system bodies include in their payload instruments measuring the emerging radiation in the infrared range. For the interpretation of the measured data an emissivity spectral library of planetary analogue materials is needed.
The Berlin Emissivity Database (BED) is focused on relatively fine-grained size separates, providing a realistic basis for interpretation of thermal emission spectra of planetary regoliths. The BED is therefore complimentary to existing thermal emission libraries, like the ASU library for example. The Berlin Emissivity Database (BED) currently contains emissivity spectra of plagioclase and potassium feldspars, low Ca and high Ca pyroxenes, olivine, elemental sulphur, Martian analogue minerals and volcanic soils, and a lunar highland soil sample measured in the wavelength range from 3 to 16 µm as a function of particle size. For each sample we measured the spectra of four particle size separates: <25, 25-63, 63-125 and 125-250 µm. These size separates have been selected to truly represent most of the planetary surfaces.
The spectral measurements are performed with a Fourier transform infrared spectrometer Bruker IFS 88, purged with dry air and equipped with a liquid-nitrogen-cooled HgCdTe (MCT) detector. The spectrometer is attached to an external emissivity chamber, a double-walled box with three apertures:
A heater is installed in the chamber and is used to heat the cup with the samples from the bottom. The thermal radiation emitted normal to the surface by the sample or the blackbody is collected by an rotatable Au-coated parabolic off-axis mirror and reflected to the entrance port of the spectrometer. A pump circulates water at a constant temperature (20° C or lower) in the volume between the inner and outer walls of the chamber. The surfaces of the box are painted with black high emissivity paint. The chamber is purged with dry air to remove particulates, water vapour and CO2. All spectra were acquired with a spectral resolution of 4 cm-1.