Spectral modeling techniques have been developed for the analysis of planetary surfaces using large thermal infrared (TIR) spacecraft datasets. These techniques can be applied to three main spectral analysis problems: (1) correction for atmospheric effects for the recovery of surface emissivity; (2) isolation and separation of surface spectral endmembers for the characterization of surface mineralogy; and (3) determination of surface anisothermality for the retrieval of surface physical properties and correction for thermal emission in near-infrared spectral data. These modeling techniques have been extensively applied to martian and lunar spacecraft datasets, forming a basis for the retrieval of surface physical and compositional properties.

Middle infrared (~2000 to 200 cm–1 or 5 to 50 μm) data are extremely useful for compositional determination of geologic materials because this wavelength region hosts the fundamental (“Reststrahlen”) vibrational bands of most minerals. Analysis of remotely sensed data requires comparison to well-developed spectral libraries populated with a wide variety of mid-IR mineral spectra (and additional rock or meteorite spectra). Here we present the theory behind molecular vibrations of mineral structures and the simple harmonic oscillators that define them mathematically. We present dispersion theory that describes how energy travels through a crystal and how propagating energy is affected by the crystal lattice structure, specifically along the various crystal axes. The equipment required for these types of laboratory measurements (both emissivity and reflectivity) is presented as well as a discussion about how mid-IR data are affected by particle size and how related volume scattering affects spectral data. Finally, mid-IR emissivity spectra acquired in a dry, 1-atm environment are provided for 93 different minerals and meteorites. These spectra are available as ancillary data files.