Intercomparison exercise between different radiative transfer models used for the interpretation of ground-based zenith-sky and multi-axis DOAS observations
[摘要] We present the results of an intercomparison exercise between six differentradiative transfer (RT) models carried out in the framework of QUILT, an EUfunded project based on the exploitation of the Network for the Detection ofStratospheric Change (NDSC). RT modelling is an important step in theinterpretation 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 inmulti-axis (MAX) geometry (trace gases: NO
2 and HCHO) and in takinginto account photochemical enhancement for calculating SCDs of rapidlyphotolysing species (BrO, NO
2, and OClO) in zenith-sky geometry. Concerningthe zenith-sky simulations, the different models agree generally well,especially below 90° SZA. At higher SZA, larger discrepancies are obtainedwith relative differences ranging between 2% and 14% in some cases.In MAX geometry, good agreement is found between the modelswith the calculated NO
2 and HCHO SCDs differing by no more than 5% in theelevation 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, suggestingdifferences between models in the treatment of aerosol scattering.A better agreement is found in case of the ground albedo and relativeazimuth effects. The complete set of initialization data and results havebeen made publicly available through the QUILT project web site(
http://nadir.nilu.no/quilt/), enabling the testing of other RT codesdesigned for the calculation of SCDs/AMFs.
