What about the spectral parameters when performing synergistic atmospheric measurements?

Optical measurements of atmospheric minor constituents are performed using spectrometers working in the UV-visible, infrared and microwave spectral ranges. The combined use of nadir viewing UV-visible and thermal infrared spectrometers (such as GOME2 and IASI onboard MetOP) will provide an important improvement of vertical trace gas concentration profiles. The analysis and interpretation of the corresponding atmospheric spectra require good knowledge of the molecular parameters of the species of interest as well as of the interfering species. In particular meaningful comparisons of profiles retrieved by various instruments using different spectral domains require that the spectral parameters are consistent in these spectral domains. To illustrate how this is diñcult we will discuss the problems one is facing to achieve this goal in the case of the formaldehyde molecule. For the measurement of atmospheric formaldehyde concentrations, mid-infrared and ultraviolet absorptions are indeed both used by ground, air or satellite instruments. It is then of the utmost importance to have consistent spectral parameters in these various spectral domains. Consequently the aim of the study performed at LISA was to inter- calibrate formaldehyde spectra in the infrared and ultraviolet regions. The experiments were performed by acquiring simultaneously UV and IR spectra at room temperature and atmospheric pressure using a common optical cell. The reactor contains two multiple reìection optical systems interfaced to a Fourier transform infrared spectrometer and to an UV-visible absorption spectrometer. The results of the work will be presented allowing one to point out a much better agreement with one of the various UV absorption cross sections available in the literature. If time permits, problems encountered when comparing the spectral parameters of the ozone molecule in various spectral domains will be discussed