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4A/OP


The software 4A/OP subroutine, called 4A/OP-sub hereafter, is the subroutine version of the code 4A-SWIR-TIR.

The objective of the software is to allow the fast simulation of the atmospheric radiative transfer in particular over the thermal and near infrared range either with a “pseudo-infinite” (high) resolution or with a spectral resolution of the simulated instruments.

The 4A model is a line-by-line model. It allows a rapid computation of the radiative transfer without accuracy loss thanks to a prior creation of an optical thickness database. This database named Atlas contains the monochromatic optical thicknesses for the various atmospheric constituents (Scott and Chédin, 1981). The atlases are created once and for all by using the line-by-line and layer-by-layer model, STRANSAC (Scott, 1974) in its latest 2012 version with up to date spectroscopy from the GEISA spectral line catalogue (Jacquinet-Husson et al., 1999, 2003, 2008 2009, 2016). This concept has been developed and maintained at the Laboratoire de Météorologie Dynamique (LMD) under the abbreviation 4A for Automatized Atmospheric Absorption Atlas.

 4A output is the radiance spectrum in a user-defined spectral domain in the infrared and near-infrared region; the usual spectral domain is between 495 and 13290 cm-1 (20-0.76 µm). 4A can be used for a wide variety of surface and earth atmospheric conditions; its use could be extended to extra-terrestrial atmospheric conditions. Spectra are computed at high spectral resolution (the nominal spectral resolution is 5.10-4 cm-1, but it can be changed by users). They can also be convolved with various types of instrument function. Jacobians, i.e. partial derivatives of the radiance with respect to the temperature and gas mixing ratio, can be also computed. They allow the model coupling with an inversion algorithm for the atmospheric constituent retrieval from infra-red radiance measurements.

The 4A/OP-sub is an heritage of the 4A program for the needs of the inversion issues and was developed under funding by CNRS and from CNES programs. Further development is supported by CNES.

The main scientific functions included in 4A/OP-sub are listed below:

  • User-defined spectral emissivity/reflectance/brdf functions;
  • Spherical atmosphere;
  • Solar spectral contribution;
  • Limb viewing including refraction;
  • Scattering for molecular, aerosol and cirrus contribution;
  • Simulation in polarized light;
  • Jacobian computation of temperature profile, atmospheric molecule profiles, surface pressure, emissivity and temperature and aerosol optical thickness;
  • Convolution with instrument functions;
  • The new possibility to define the input spectral limits and the instrumental functions in wavelength.

References :

L. Chaumat, E. Dufour, B. Tournier and C. Standfuss, 2010 : Extension de 4A/OP au domaine du proche infrarouge, NOV-3810-NT-8259_v2.0.

L. Chaumat and C. Standfuss , 2010: Développement de 4A/OP-SWIR, NOV-3865-NT-9881.

L. Chaumat, N. Lautier, O. Lezeaux and C. Standfuss, 2011 : Développement algorithmique et scientifiques de 4A/OP SWIR, NOV-3933-NT-11703_v1.2.

B. Tournier, C. Standfuss and T. Lalanne, 2012: Développement de 4A/OP SWIR, NOV-7139-NT-1519_v1.1.

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.

Tournier, B., R. Armante, and N. A. Scott, 1995: STRANSAC-93 et 4A-93: Développement et validation des nouvelles version des codes de transfert radiatif pour application au projet IASI. Internal Rep. LMD, No. 201, LMD/CNRS, Ecole Polytechnique, PALAISEAU, France.

Scott, N. A., 1974: A direct method of computation of transmission function of an inhomogeneous gaseous medium: description of the method and influence of various factors. J. Quant. Spectrosc. Radiat. Transfer, 14, 691-707.

Jacquinet-Husson, N. et al., 1999: The 1997 spectroscopic GEISA data bank. J. Quant. Spectrosc. Radiat. Transfer, 62, 205-254.

Jacquinet-Husson, N., N. A. Scott, A. Chedin, and A. A. Chursin, 2003: The GEISA spectroscopic database system revisited for IASI direct radiative transfer modelling. Atmospheric and Oceanic Optics, 16, N°3, 256-282.

Jacquinet-Husson, N. et al., 2008: The GEISA spectroscopic database: Curent and future archive for Earth and planetary atmosphere studies. J. Quant. Spectrosc. Radiat. Transfer, 109, 1043-1059.

Jacquinet-Husson, N. et al., 2009: The 2009 edition of the GEISA spectroscopic database. J. Quant. Spectrosc. Radiat. Transfer, 112, 2395-2445.

Jacquinet-Husson, N. et al., 2016: The 2015 edition of the GEISA spectroscopic database. J. Quant. Spectrosc. Radiat. Transfer, 327, 31-72.

License :

Open-Source software, licensed under the LGPL

Atlas :

In order to get the Atlas database, please contact 4A/OP Support

Programming Language :

Fortran 77, 90

Supported Operating Systems :

RedHat/CentOS 6.4 64bit, RedHat/CentOS 7.2 64bit

Contact :

4A/OP Support or go to the Contact page