Ten years of MIPAS measurements: what about spectroscopy ?

MIPAS (Michelson Interferometer for Passive Atmospheric Sounding) is a Fourier transform spectrometer designed for measuring the earth atmospheric emission at limb in the 685-2410 cm-1 range. It flew onboard the polar orbit ENVISAT satellite for approximately 10 years, from June 2002 to April 2012, performing measurements during both day and night with an unprecedented spectral resolution from space (0.025 cm-1 in the first part of the mission and 0.0625 cm-1 in the second part). MIPAS measurements on ENVISAT represent a unique database for the study of the vertical distribution and time variation of the atmospheric composition on a global scale. While the focus of the instrument is the study of the chemistry and the physics of the stratosphere, also information on constituents in the upper troposphere has been derived. The ESA products include more than 20 minor atmospheric constituents [1]. The retrieval of the vertical profiles of atmospheric constituents is performed by fitting the observations to a full-physics model taking into account emission and absorption of all molecules. As a consequence the possibility of performing the retrievals is directly linked to the availability of the spectroscopic parameters and the quality of the retrieval depends on their quality. Indeed, in the estimation of the total error budget of the retrieved profiles the error due to the spectroscopic database is often one of the largest ones. The need of exploiting the information contained in the measurements of MIPAS, as well as of other instruments operating in the same spectral region like ACE-FTS, has driven studies for improving spectroscopic parameters in the middle infrared spectral region. MIPAS measurements provided not only the motivation, but also the guideline and the validation of the spectroscopic studies. Thanks to the their high spectral resolution and broadband coverage, the differences between observations and simulations of MIPAS measurements have been used to detect inconsistencies and validate subsequent improvements in the spectroscopic database (obtained with laboratory measurements and new calculations). In some cases MIPAS measurements have been used to convert the relative line intensities of a given spectral band to absolute intensities by comparing the retrieved profiles from MIPAS radiances from two different regions covering the two different spectral bands [2]. In this talk we will show how MIPAS measurements were used to validate the most recent improvements in the spectroscopic database of HNO3 and COCl2.