Adequate tools are required to perform reliable radiative transfer modelling calculations to meet the needs of communities involved in understanding the atmospheres of the Earth and other planets. Among these tools compilations of spectroscopic parameters are used for a vast array of applications and especially for planetary atmospheric remote sensing. Consequently, there is an acute need for comprehensive, trustworthy and operational interactive spectroscopic databases to benefit the research in direct and inverse radiative transfer. In this context, since over three decades, the ARA (Atmospheric Radiation Analysis) group at LMD (Laboratoire de Météorologie Dynamique, France) has developed GEISA (Gestion et Etude des Informations Spectroscopiques Atmosphériques: Management and Study of Atmospheric Spectroscopic Information), a computer accessible database system [Chédin et al. (1982), Husson et al. (1992), Jacquinet-Husson et al.(1999, 2008, 2009)], designed to facilitate accurate and fast forward, calculations of atmospheric radiative transfer using a line-by-line and (atmospheric) layer-by-layer approach. This effort has proven to be beneficial to the atmospheric scientific community participating in direct and inverse radiative transfer studies.

The role of molecular spectroscopy in modern atmospheric research has entered a new phase with the advent of highly sophisticated spectroscopic instruments and computers. For example, the performance of Earth atmospheric sounders like AIRS, in the USA, and IASI in Europe, which have a better vertical resolution and accuracy, compared to the previous existing satellite infrared vertical sounders, is directly related to the quality of the spectroscopic parameters of the optically active gases, since these are essential input in the forward models used to simulate recorded radiance spectra. Consequently, a strong demand exists for highly comprehensive, well validated, efficiently operational, and desirably interactive computer-based spectroscopic databases to benefit the research in direct and inverse radiative transfer.

In this purpose, GEISA is currently involved in activities related to the assessment of the capabilities IASI through the GEISA/IASI database, extensively described in Jacquinet-Husson et al. (2005). Since the METOP European polar satellite launch (October 19th 2006) , GEISA/IASI is the reference spectroscopic database for the validation of the level-1 IASI data, using the 4A (Automatized Atmospheric Absorption Atlas) radiative transfer model [Scott (1974), Scott and Chédin (1981); 4A/LMD ; 4A/OP co-developed by LMD and Noveltis with the support of CNES].

GEISA is maintained :

• by the Ara group at LMD (Ecole Polytechnique) for its scientific part
• by the group (CNRS Centre National de la Recherche Scientifique-France) at IPSL (Institut Pierre Simon Laplace) for its technical part.