Use of hyperspectral infrared radiances to infer atmospheric trace gases

Hyperspectral infrared instruments operating in nadir (AIRS, IASI, TANSO-FTS, CrIS, IASI-NG) or limb (MIPAS, ACE-FTS) viewing modes provide high-resolution atmospheric spectra from which it is possible to retrieve information on many geophysical variables during both day and night. In particular, such instruments allow the simultaneous measurements of a series of atmospheric trace gases (e.g., H₂O, CO₂, O₃, N₂O, CO, CH₄, CFCs, SO₂, NO₃, etc.) that can be divided into greenhouse gases and chemical reactive gases. Retrieving gas concentration from infrared observations relies on forward radiative transfer computation, using spectroscopic knowledge on atmospheric species, and inverse approaches, which are based on minimization schemes optimized for the instrument and the targeted species. The accuracy and vertical information achievable for a given species depends on the strength of its spectral signature and on the spectral and radiometric characteristics of the instrument. Probing the atmospheric boundary layer also requires high thermal contrast between the ground and the first atmospheric layers. Confined for many years to the study of meteorological variables, instruments operating in the thermal infrared are now a central part of atmospheric composition and climate studies.