A FIELD-PORTABLE THERMAL INFRARED GRATING SPECTROMETER (THIRSPEC)

A thermal infrared grating spectrometer was developed for field studie s in the earth sciences. The design is based on a reflection grating a nd a 60-element HgCdTe detector array. The useful spectral range of th e instrument covers 7.9-11.3 mum with a Nyquist limited resolution of 0.16 mum. The instrument averages over a 12-degrees field of view and compares the exitance of the target to that of an internal black body at ambient temperature. The noise equivalent temperature is approximat ely 0.06-degrees-K over the useful spectral range. Background radiance reflected from the surface of the target can seriously impede the det ermination of emissivity. This eff ect is removed from the spectra of geological samples by the use of reference samples.