BED Emissivity Spectral Library

Remote-sensing infrared spectroscopy is the principal field of investigation for planetary surfaces composition. Past, present and future<br>missions to the solar system bodies include in their payload, instruments measuring the emerging radiation in the infrared range. Apart<br>from measuring the reflected radiance, more and more spacecrafts are equipped with instruments measuring directly the emitted<br>radiation from the planetary surface.<br>The emitted radiation is not only a function of the composition of the material but also of its texture and especially the grain size<br>distribution. For the interpretation of the measured data an emissivity spectral library of planetary analogue materials in grain size<br>fractions appropriate for planetary surfaces is needed. The Berlin emissivity database (BED) presented here is focused on relatively finegrained<br>size separates, providing thereby a realistic basis for the interpretation of thermal emission spectra of planetary regoliths. The<br>BED is therefore complimentary to existing thermal emission libraries, like the ASU library for example. BED currently contains<br>emissivity spectra of plagioclase and potassium feldspars, low Ca and high Ca pyroxenes, olivine, elemental sulfur, Martian analogue<br>minerals and volcanic soils, and a lunar highland soil sample measured in the wavelength range from 7 to 22 µm as a function of particle<br>size. For each sample we measured the spectra of four particle size separates ranging from 25 to 250 µm.<br>The device we used is built at DLR (Berlin) and is coupled to a Fourier-transform infrared spectrometer Bruker IFS 88 purged with<br>dry air and equipped with a nitrogen-cooled MCT detector. All spectra were acquired with a spectral resolution of 4 cm- 1.<br>We are currently working on upgrading our emissivity facility. A new spectrometer (Bruker VERTEX 80 V) and new detectors will<br>allow us to measure the emissivity of samples in the wavelength range from 1 to 50 µm in a vacuum environment. This will be particularly<br>important for the interpretation of the MERcury Thermal Infrared Imaging Spectrometer (MERTIS) data.