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Synergistic use of different atmospheric instruments: What about the spectral parameters?

Jean-Marie Flaud(1), Benedicte Picquet-Varrault(1), Aline Gratien(1), Johannes Orphal(1) and Jean-François Doussin(1)

(1) LISA-CNRS-Uni.Paris 12 and Uni.Paris 7, 61 Av. General de Gaulle, 94010 CRETEIL, France


Optical measurements of atmospheric minor constituents are performed using spectrometers working in the UV-visible, infrared and microwave spectral ranges. In particular recently the satellite ENVISAT has been launched with three spectrometers on board, SCIAMACHY and GOMOS working in the UV-visible spectral region and MIPAS working in the thermal infrared. In the future, the combined use of Nadir-viewing UV-visible and thermal infrared spectrometers (onboard remote-sensing satellites such as OMI and TES onboard EOS-AURA, or GOME-2 and IASI onboard MetOp) will provide an important improvement of vertical trace gas concentration profiles. The analysis and interpretation of the atmospheric spectra require good knowledge of the molecular parameters of the species of interest as well as of the interfering species. This is true not only in the spectral domain used to retrieve the species (thermal infrared for MIPAS for example) but also in the other spectral domains used by other instruments: Meaningful comparisons of profiles retrieved by various instruments using different spectral domains require indeed that the spectral parameters are consistent in these spectral domains. To illustrate these points we will concentrate on two molecules namely ozone and formaldehyde.

In the mid-infrared range, the 10 µm ozone band is very strong and is the most widely used to derive concentration profiles. In the UV region, the Huggins and/or Hartley bands are currently used for spectroscopic remote-sensing of ozone. In this talk we will present two sets of results: - First a careful comparison of four sets of ozone line intensities measured independently in the 10 µm region has been achieved. From them new and more accurate transition moment constants for the ν1 and ν3 bands of 16O3 were derived and used to generate new line positions and intensities. These new spectroscopic parameters allowed one to simulate atmospheric spectra better than the previous spectroscopic parameters showing that on a relative basis the new spectral parameters are of better quality [1]. - Second, there have been rather few intercomparisons of ozone absorption cross sections in the UV and mid-infrared regions. We will present the results of such comparisons either between the 10 µm region and the absorption of ozone at 254 nm or between the 10 µm and the Huggins band showing that still some inconsistencies at the level of 4-5% exist.

For the measurement of atmospheric formaldehyde concentrations, mid-infrared and ultraviolet absorptions are 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 intercalibrate 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 reflection optical systems interfaced to a Fourier transform infrared spectrometer and to a 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.

References [1] J. M. Flaud, G. Wagner, M. Birk, C. Camy-Peyret, C. Claveau, M. R. De Backer-Barilly, A. Barbe, and C. Piccolo, Ozone absorption around 10 μm, J. Geophys. Res., Vol. 108, NO. D9, 4269, doi:10.1029/2002JD002755, 2003


Full paper

Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry