Intercomparison exercise between different radiative transfer models used for the interpretation of ground-based zenith-sky and multi-axis DOAS observations F. Hendrick1, M. Van Roozendael1, A. Kylling2,*, A. Petritoli3, A. Rozanov4, S. Sanghavi5, R. Schofield6,**, C. von Friedeburg5, T. Wagner5, F. Wittrock4, D. Fonteyn1, and M. De Mazière1 1Institut d’Aéronomie Spatiale de Belgique, Brussels, Belgium 2Norwegian Institute for Air Research, Kjeller, Norway 3Institute of Atmospheric Science and Climate, Bologna, Italy 4Institute of Environmental Physics, University of Bremen, Bremen, Germany 5Institute of Environmental Physics, University of Heidelberg, Heidelberg, Germany 6National Institute of Water and Atmospheric Research, Omakau, Central Otago, New Zealand *now at: St. Olavs University Hospital, Trondheim, Norway **now at: NOAA Aeronomy Laboratory, Boulder, Colorado, USA
Abstract. We present the results of an intercomparison exercise between six different
radiative transfer (RT) models carried out in the framework of QUILT, an EU
funded project based on the exploitation of the Network for the Detection of
Stratospheric Change (NDSC). RT modelling is an important step in the
interpretation of Differential Optical Absorption Spectroscopy (DOAS)
observations. It allows the conversion of slant column densities (SCDs)
into vertical column densities (VCDs) using calculated air mass factors
(AMFs). The originality of our study resides in comparing SCD simulations in
multi-axis (MAX) geometry (trace gases: NO2 and HCHO) and in taking
into account photochemical enhancement for calculating SCDs of rapidly
photolysing species (BrO, NO2, and OClO) in zenith-sky geometry. Concerning
the zenith-sky simulations, the different models agree generally well,
especially below 90° SZA. At higher SZA, larger discrepancies are obtained
with relative differences ranging between 2% and 14% in some cases.
In MAX geometry, good agreement is found between the models
with the calculated NO2 and HCHO SCDs differing by no more than 5% in the
elevation and solar zenith angle (SZA) ranges investigated (5°–20°
and 35°–85°, respectively). The impacts of aerosol scattering,
ground albedo, and relative azimuth on MAX simulations have also been tested.
Significant discrepancies appear for the aerosol effect, suggesting
differences between models in the treatment of aerosol scattering.
A better agreement is found in case of the ground albedo and relative
azimuth effects. The complete set of initialization data and results have
been made publicly available through the QUILT project web site
(http://nadir.nilu.no/quilt/), enabling the testing of other RT codes
designed for the calculation of SCDs/AMFs.
Citation: Hendrick, F., Van Roozendael, M., Kylling, A., Petritoli, A., Rozanov, A., Sanghavi, S., Schofield, R., von Friedeburg, C., Wagner, T., Wittrock, F., Fonteyn, D., and De Mazière, M.: Intercomparison exercise between different radiative transfer models used for the interpretation of ground-based zenith-sky and multi-axis DOAS observations, Atmos. Chem. Phys., 6, 93-108, doi:10.5194/acp-6-93-2006, 2006.