4A heritage is from 4A2000 with its initial development at LMD supported under CNRS and CNES programs. CNES and CNRS support the continued advancements of 4A, through a subcontract with NOVELTIS. Software 4A consolidation is NOVELTIS’ responsibility and it aims at completing a product easy to use by several research groups or to be integrated in operational processing chains. The resultant product is 4A/OP.
The 4A code has been developed in Fortran 77 under the Unix system. It has been recently rewritten in standard Fortran 90 and it runs on any platform with Fortran 90 compiler and C compiler. Memory usage is moderate (about 200 Megabytes), and there are no special hardware requirements.
The code development is under CVS.

4A is maintained at LMD which includes introducing all the newly derived parameters for spectroscopy, for line-coupling or for continua, for aerosols and CFCs, …, as soon as they have been validated. The current version is referred to as 4A-2000.

Click here for references and publications.

4A/OP on Wikipedia.

4A/OP poster presented at the 16th International TOVS Study Conference (ITSC-16) in May 2008.

4A/OP poster presented at the 2nd IASI International Conference in January 2010.

4A/OP poster presented at the 18th International TOVS Study Conference (ITSC-18) in March 2012.

Success Stories

4A/OP was chosen by CNES as official RTM for IASI level1 CAL/VAL and level1 operational processing.

Click here for references on validation campaigns.

Spectroscopic parameters

The GEISA (Gestion et Etude des Informations Spectroscopiques Atmosphériques: Management and Study of Atmospheric Spectroscopic Information) computer accessible database system, is developed, maintained and regularly updated by the ARA (Atmospheric Radiation Analysis) group at LMD since the late 70’s..
An important update of GEISA has been performed in 2003 and is being issued for the international community interactive use.
The GEISA system comprises three databases with their associated management software:

The facilities are available at GEISA.

Currently, GEISA is involved in forward modeling activities with the purpose of assessing the IASI measurements capabilities, within the ISSWG (IASI Sounding Science Working Group), in the frame of the CNES (Centre National d’Etudes Spatiales, France)/EUMETSAT (EUropean organization for the exploitation of METeorological SATellites) Polar System (EPS).

Referencing 4A/OP in publications

If a user is presenting results obtained using 4A/OP, the most complete way to reference it would be to reference the following:

  • Scott, N.A. and A. Chedin, 1981: A fast line-by- line method for atmospheric absorption computations: The Automatized Atmospheric Absorption Atlas. J. Appl. Meteor., 20, 802-812.
  • L. Chaumat, C. Standfuss, B. Tournier, E. Bernard, R. Armante and N. A. Scott, 2012: 4A/OP Reference Documentation, NOV-3049-NT-1178-v4.3, NOVELTIS, LMD/CNRS, CNES, 311 pp.