This code predicts the satellite signal from 0.25 to 4.0 micrometers assuming a
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
The following input parameters are needed
Atmospheric model for gaseous components
Aerosol model (type and concentration)
Ground reflectance (type and spectral variation)
At each step, you can either select some standard conditions (for example, spectral
bands of satellite for spectral conditions) or define your own conditions.
The authors of this package are:
6S code: Vermote E. et al
Motif code: Gonzalez L. et al
Laboratoire d'Optique Atmospherique
Universite des Sciences et
Technologies de Lille
59655 Villeneuve d'Ascq Cedex - France
Reading - England
Code 923 / GIMMS group
Greenbelt, MD 20771 - USA
Limits of validity
The visibility must be better
than 5.0 km. For lower values,
the calculations might be not
The gaseous transmittance and
the scattering functions are
valid between 0.25 and 4.0
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
You can consider a patchy
structure, i.e. a circular
target of defined radius,
surface reflectance and
You can also consider uniform
surface conditions with a
directional reflectance as
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.
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
Commercial and other users: Use of this
package in commercial applications is
strictly forbidden without a written
approval of the authors.