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BED Emissivity Spectral Library

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posted on 2015-09-07, 12:33 authored by Alessandro MaturilliAlessandro Maturilli

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. Apart
from measuring the reflected radiance, more and more spacecrafts are equipped with instruments measuring directly the emitted
radiation from the planetary surface.
The emitted radiation is not only a function of the composition of the material but also of its texture and especially the grain size
distribution. For the interpretation of the measured data an emissivity spectral library of planetary analogue materials in grain size
fractions appropriate for planetary surfaces is needed. The Berlin emissivity database (BED) presented here is focused on relatively finegrained
size separates, providing thereby a realistic basis for the interpretation of thermal emission spectra of planetary regoliths. The
BED is therefore complimentary to existing thermal emission libraries, like the ASU library for example. BED currently contains
emissivity spectra of plagioclase and potassium feldspars, low Ca and high Ca pyroxenes, olivine, elemental sulfur, Martian analogue
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
size. For each sample we measured the spectra of four particle size separates ranging from 25 to 250 µm.
The device we used is built at DLR (Berlin) and is coupled to a Fourier-transform infrared spectrometer Bruker IFS 88 purged with
dry air and equipped with a nitrogen-cooled MCT detector. All spectra were acquired with a spectral resolution of 4 cm-1.
We are currently working on upgrading our emissivity facility. A new spectrometer (Bruker VERTEX 80 V) and new detectors will
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
important for the interpretation of the MERcury Thermal Infrared Imaging Spectrometer (MERTIS) data.