====== Molecular absorption from ARTS ======

Example included in: 
      /home/data/daten/public/rt-data/arts/generate_moltau

==== Instructions from README file ====

This directory includes an example, how to perform a line-by-line calculation
with DISORT using absorption coefficients generated by the ARTS model
(http://www.sat.ltu.se/arts/). 

ARTS is installed in the directory 
   /home/opt/arts 
the executable is accessable as 
   /home/opt/bin64/arts 

In order to have ARTS default settings please set the following
environment variable in your shell: 
   export ARTS_INCLUDE_PATH=/home/opt/arts/includes/

===Running ARTS===

The file gen_moltau.arts provides an ARTS control file example which
can be run as follows: 
    arts gen_moltau.arts
With this setup ARTS generates line-by-line absorption
coefficients in the wavelength range from 10.00 to 10.01 microns using
1000 grid points (equally spaced in frequencies). Please see also the
comments in the file, ARTS writes a molecular_tau_file called
moltau_example.nc in netcdf format. 

Try arts -d ... to get help for the individual ARTS functions. The ARTS user 
guide is available at 
   /home/opt/arts/build/doc/uguide/arts_user/arts_user.pdf

===Running uvspec===

uvspec_lbl.ir.disort.inp is an example input file for uvspec, which
uses the molecular_tau_file from ARTS. Running this file should
produce uvspec_lbl.ir.disort.out.

Note that the altitudes, pressures, and temperatures in the
atmosphere_file must correspond to the atmosphere that was used in
ARTS. ARTS also includes the FASCOD standard atmospheres (as
libRadtran) but only up to an altitude of 95km. For this reason, the
file afglms.dat is included here, which is the standard
midlatitude-summer atmosphere from the libRadtran/data/atmmod
directory cut above 95km. 
(If you want to use an atmosphere different from the standard
atmospheres please contact me, I have a script to easily generate
consistent atmosphere files.)

 --- //[[claudia.emde@lmu.de|Claudia]] 2010/07/28 14:46//

==== Comparison of ARTS and DISORT radiances ====

computation directory: 
   ~/arts_stuff/gen_moltau/tests/comp_arts_librad_10.1_10.2um

[{{:libradtran_devel:nadir_comparison.png?800|Comparison for Nadir, TOA}}]

Here a comparison for TOA nadir radiances is shown for DISORT, tzs (thermal zero scattering) and ARTS. Differences are mostly below 0.1% which is ok. The calculation was made for the standard midlatitude-summer atmosphere.

[{{:libradtran_devel:zenit_comparison.png?800|Comparison for Zenith, BOA}}]

Here a comparison for BOA nadir radiances is shown for DISORT, and ARTS. For the standard midlatitude-summer atmosphere the differences are as much as 5%!! Doing the same calculation with 1000 layers the models approach each other in the middle which shows that the difference is due to different vertical interpolation schemes. In ARTS T and babs are linearly interpolated, and the Planck emission is calculated from the interpolated values. In libRadtran an average absorption coefficient is taken for each layer and the Planck function is linearly interpolated.