Introduction
------------

The present radiative transfer (RT) model validation package is the 
deliverable of the workpackage (WP) 2500 of the QUILT project (European 
Commission, EVK2-2000-00545). Its purpose is to enable the testing of RT 
codes aiming to the calculation of AMFs(air mass factors)/slant columns as 
required for ground-based DOAS (Differential Optical Absorption 
Spectroscopy) and MAX-DOAS applications. The package focus on the 
simulation of:

(1) Zenith-sky observations of BrO, NO2, and OClO, taking into account the
photochemical variation of these species
(2) MAX observations of NO2 and HCHO, the photochemical 
variation of the species being not taken into account in this case

The initialization data and results come from an intercomparison exercise 
between six RT models carried out within the framework of the QUILT 
WP2500. The different models and comparison tests are described in a 
paper entitled "Intercomparison exercise between different radiative 
transfer models used for the interpretation of ground-based zenith-sky and 
multi-axis DOAS observations" by Hendrick et al. This paper has been submitted 
for publication to ACPD (www.copernicus.org/EGU/acp/acpd). A copy of this paper 
in pdf format is included in the present package.
 
In brief, the following tests have been performed (see the paper 
for more details on the initialization conditions):

* Calculation of BrO, OClO, and NO2 SCDs for sunset conditions in 
zenith-sky geometry, single (SS) and multiple scattering (MS) modes 
* Calculation of NO2 and HCHO SCDs in MAX geometry, MS mode and for 
90° of azimuth angle of line of sight. The elevation degrees are 5°, 
10°, and 20° for both species.
* Test on the impact of aerosol scattering in MAX geometry: Calculation 
of NO2 and HCHO SCDs with and without aerosol scattering in MS mode, 
for 90° of azimuth angle of line of sight, and for 5°, 10°, and 20° of 
elevation
* Test on the impact of the ground albedo in MAX geometry: Calculation of 
NO2 and HCHO SCDs for ground albedo values of 0 and 0.9 in MS mode, for 90° of 
azimuth angle of line of sight, and for 5°, 10°, and 20° of elevation

The plots of the single profiles used for the tests in MAX geometry 
appear in the paper. Absorption by O3 is included in all calculations. 
Absorption by NO2 is also included in the calculation of BrO, OClO, and 
HCHO SCDs.


How to use the RT validation package ?
--------------------------------------

1/Extraction of the files from the file "rtm_validation_package.zip"

All the files (data + paper) must be extracted from the 
file "rtm_validation_package.zip" with the option "Use folder names" 
activated. Data are in ascii format and are stored into two main folders 
entitled "initialization_data" and "results". The folder 
"initialization_data" is structured in 5 sub-folders: 4 sub-folders 
entitled "zenith", "max", "aerosol_test_max", and "albedo_test_max" and 
containing the initialization data specific to each test. The fifth sub-folder 
entitled "xs" contains the cross-sections data common to the four tests. 
The folder "results" is structured in 4 sub-folders entitled "zenith", "max", 
"aerosol_test_max", and "albedo_test_max" and containing the results of each test.

2/Example of SCDs calculation

In order to calculate BrO SCDs in zenith-sky geometry, the following files 
are needed:

*In sub-folder "zenith" of the folder "initialization_data":
# bro_matrice_pm.dat: sunset variation table of BrO concentration
# sza_pm_bro_oclo.dat: solar zenith angles corresponding to the profiles 
given in the file bro_matrice_pm.dat
# altitude_grid_bro_oclo_no2.dat: altitude grid used for the calculation of 
BrO, OClO, and NO2 SCDs
# o3_pro_bro_oclo.dat: O3 profile used for the calculation of BrO SCDs
# no2_pro_bro_oclo.dat: NO2 profile used for the calculation of BrO SCDs
# pres_temp_bro_oclo.dat: Pressure and temperature profiles used for the 
calculation of BrO SCDs
# dens_air_bro_oclo.dat: Air density profile used for the calculation of 
BrO SCDs 

"bro_oclo" in the file name means that this file is common for BrO and OClO 
SCDs calculations.

*In sub-folder "xs" of the folder "initialization_data":
# bro.xs: set of BrO absorption cross-sections
# o3.xs: set of O3 absorption cross-sections
# no2.xs: set of NO2 absorption cross-sections

The same file names rules are applicable to the other tests. It should be 
noted that the initialization profiles are the same for the three tests in 
MAX geometry ("max", "aerosol_test_max", and "albedo_test_max"). Concerning 
the other conditions of initialization (wavelength, ground albedo, aerosol 
conditions,...), please look at the paper.

3/Comparison with the calculations performed using the QUILT RT models

For example, BrO SCDs calculated in "zenith" using the QUILT RT 
models are stored in the sub-folder "zenith" of the folder 
"results" under the names "bro_pm_ms.dat" (MS mode) and "bro_pm_ss.dat" 
(SS mode). An interpretation of the results can be found in the paper.


Contact
-------

For any informations or comments, please contact François Hendrick at 
the Belgian Institute for Space Aeronomy (IASB-BIRA). 
E-mail: franch@oma.be.
Version 2.0 edited on 23/06/2005