À propos

This code predicts the satellite signal from 0.25 to 4.0 micrometers assuming a cloud-free atmosphere.
The main atmospheric effects (gaseous absorption by water vapor, carbon dioxyde, oxygen and ozone, scattering by molecules are taken into account. Non-uniform surfaces can be considered, as well as a bidirectional reflectance, as boundary conditions.

The following input parameters are needed

• Geometrical conditions
• Atmospheric model for gaseous components
• Aerosol model (type and concentration)
• Spectral condition
• Ground reflectance (type and spectral variation)

	The authors of this package are:
	6S code:    Vermote  E. et al
	Motif code: Gonzalez L. et al

	From:

	Laboratoire d'Optique Atmospherique
	Universite des Sciences et
	              Technologies de Lille
	59655 Villeneuve d'Ascq Cedex  -  France

	E.C.M.W.F.
	Reading  -  England

	Code 923 / GIMMS group
	GSFC/NASA
	Greenbelt, MD 20771  -  USA
	

Limits of validity

• Geometrical parameters:

  No limitations.

• Atmospheric model:

  No limitations.

• Aerosol model:

  The visibility must be better than 5.0 km. For lower values, the calculations might be not valid.

• Spectral conditions:

  The gaseous transmittance and the scattering functions are valid between 0.25 and 4.0 micrometers.
  However the computation of the interaction between absorption and scattering is correct only for low absorption values.
  If you want to compute a signal within an absorption band, that interaction should be reconsidered.

• Ground reflectance:

  • You can consider a patchy structure, i.e. a circular target of defined radius, surface reflectance and environment reflectance.
  • You can also consider uniform surface conditions with a directional reflectance as boundary conditions. Some analytical models are available, in which you can enter your own values. The code assumes that the BRDF is spectrally independent.
  • Spectral variation: 4 surface reflectances are available, which are defined in a given spectral range, depending on the selected case. Caution: the reflectance value is set to 0 outside this range due to the lack of data.

BRDF

For considering BRDF, we have to compute the downward radiance over the whole hemisphere. That is performed using the successive orders of scattering method.
That method requires numerical integration over the zenithal angles and the optical depth. The integration method is the Gauss method , where nmu (set to 24) is the number of angles, which the accuracy of the computation is obviously depending on.
The downward radiance is computed for nmu values of the zenithal angle and np values (set to 13) of the azimuthal angle.
The integration of the product of the radiance by the BRDF is so performed over the (nmu * np) values.

Copyrights: L.O.A (1994)
Academic users: You are authorized to use this code for your research and teaching. You are encouraged to distribute, free of charge, the unmodified version of this software to colleagues involved in similar activities. You may not sell this code to anybody, and you may not distribute it to commercial interests under any circumstances.
Commercial and other users: Use of this package in commercial applications is strictly forbidden without a written approval of the authors.