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Abstract
Fourier transform emission spectroscopy can make an important contribution in the observation of the Earth's atmosphere and in the investigation of atmospheric physics and chemistry. In this paper, we report the measurement performances and the result obtained by a Fourier transform spectrometer, named SAFIRE-A (Spectroscopy of the Atmosphere using Far Infrared Emission - Airborne), operating in the far infrared spectral region from limb sounding observation of the atmospheric emission from a high altitude aircraft. After a short review of the advantages of FTS emission limb sounding in comparison with competing techniques and observation geometries, a detailed description of the instrument is given with the result obtained during the APE-GAIA (Airborne Polar Experiment - Geophysica Aircraft In Antarctica) fi eld campaign carried out over the Antarctic Peninsula.
Highlights
A number of chemical, dynamic and radiative processes affecting the physical structure and the composition of the Earth’s atmosphere, can be investigated by measuring spontaneous thermal emission of atmospheric molecules
SAFIRE-A is a particular implementation of the Martin-Puplett (Martin and Puplett, 1969) polarising FT spectrometer specially designed for airborne operation (Carli et al, 1969)
Emission FT spectroscopy from airborne platform combines the intrinsic advantages of high sensitivity and selectivity of Fourier Transform Spectroscopy (FTS) instruments with the versatility of the aircraft platform, obtaining a multi-purpose tool for the characterisation of upper troposphere/ lower stratosphere air masses
Summary
A number of chemical, dynamic and radiative processes affecting the physical structure and the composition of the Earth’s atmosphere, can be investigated by measuring spontaneous thermal emission of atmospheric molecules. Emission measurements provide a better geographical and temporal coverage compared to absorption measurements. They do not need an external radiation source and can be performed continuously (both day and night) in all directions. This overcomes the poor latitude coverage of occultation measurements and makes it possible to monitor several key processes that involve chemical species with a diurnal cycle. Observations of the signal emitted by atmospheric molecules are only possible within the frequency range with significant thermal emission from the atmosphere; this includes the middle/far infrared and the millimetre-wave spectral regions. The boundaries of the operative range of emission measurements are defined by a low frequency cutoff (approximately 3 cm-1) caused by the limits of optical instruments (to which this discussion is confined) and by a high frequency cut-off (approximately 3000 cm-1) due to the low number of emitted photons
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