Data Analysis
A broadband infrared spectrum (Fig. 1) shows absorption
of many atmospheric trace gases:
Fig.1: Broadband spectrum recorded with an MCT detector.
The broadband infrared spectra (Fig. 1) were devided into
small spectral regions, so called microwindows. They have been selected
for each trace gas to be retrieved. In order to derive column amounts of
trace gases from the recorded spectra synthetic spectra were calculated
by the line-by-line and layer-by-layer algorithm KOPRA
(Karlsruhe Optimized and Precise Radiative transfer Algorithm) for each
microwindow. The synthetic spectra were fitted to the measured ones by
the software package PROFFIT
(PROFile FIT). PROFFIT allows to retrieve volume mixing ratio (vmr) profiles
and to scale partial or total vmr profiles. PROFFIT allows to fit several
species simultaneously in several microwindows. The line shape of the absorption
line is used to derive profile. For further informations about PROFFIT
please click here. To make sure
that the line shape is reproduced correctly by the instrument cell measurements
are made and analysed with LINEFIT.
Fig.2: Fitted ('Rechnung') and measured ('Messung') spectrum along
with their residuals.
Just an example for an O3 profile:
Fig.3: O3 profile
as measured with ground-based FTIR at Kiruna on 2001-07-08.
Profiles have been retrieved for species with pressure
dependent absorption lines like CH4,
N2O, HCl, HF, HNO3,
NO, and and O3, for other species
like ClONO2, NO2,
and CFCs column amounts are obtained. Thus, time series of profiles and
column amounts of these species are obtained, for example for O3:
Fig.4: Time series of zenith column amounts of O3
during winter 1997/98, compared with model results obtained with
KASIMA
(KArlsruhe SImulation Model of the middle Atmosphere).
