A new spectroscopic observatory in Cr

1
A new spectroscopic observatory in Créteil to
measure atmospheric trace gases in solar
occultation geometry
C. Viatte, P. Chelin, M. Eremenko, C. Keim, J.-M.
Flaud, J. Orphal, M. Ray Laboratoire
Inter-Universitaire des Systèmes Atmosphériques
(LISA), CNRS, Universités de Paris 12 (Paris-Est)
et Paris 7, 61 Av. du Général de Gaulle, 94010
Créteil, France.

ABSTRACT Ground-based Fourier Transform Infrared
(FTIR) and Ultraviolet (UV) spectroscopy based on
solar occultation is a powerful remote sensing
technique to determine vertical distribution of
various constituents in the atmosphere 1. In
this context, a new spectroscopic observatory
(with motorised dome rotation) was installed on
the roof of the University of Paris 12 in
Créteil. It comprises a solar tracker (Bruker
Ltd.) coupled with two spectrometers operating in
different spectral regions, to obtain information
on various atmospheric target species such as
H2O, O3, CO, CH4, N2O, NO2, HNO3, H2CO, C2H6, PAN
etc. and the most abundant isotopic species. We
have first characterized the ILS (Instrumental
Line Shape) width of the FTIR at about 0.06cm-1
using CO absorption lines in a low pressure cell.
The second step was to determine a set of
micro-windows for O3 in the infrared region that
are appropriate for retrievals of vertical
concentration profiles taking into account the
limited spectral resolution of our
instrument. The experimental data, in particular
concerning the free troposphere, will be compared
to predictions from an atmospheric chemistry
model (CHIMERE) developed at LISA in order to
improve its results, and also to satellite
observations (IASI in particular) for validation.
In addition, retrievals of the same trace gases
combining data in different spectral regions will
be attempted.
Instrumental Line Shape
Experimental setup
FWHM 0.06 cm-1
?
First Results
Solar tracker
ATMOSPHERIC SPECTRA
IR main characteristics (07-22-08 at 16.08
pm) ? OPD 8.4 cm ? 1.5 mm aperture ?
DTGS detector ? 100 scans (32 min)
? CaF2 beamsplitter

Motorised dome rotation
Set up
FTIR
IR A Fourier Transform spectrometer (Bruker
Vertex 80) is used for the infrared region 400?
15000 cm-1 with a maximum spectral resolution of
about 0.05 cm-1. UV-VIS A grating spectrometer
with a CDD array (Ocean Optics, HR 2000) is used
with 1.1 nm resolution (FWHM, sampling 0.035 nm)
and covers the spectral range of 190?1100 nm.
set of micro-windows in IR for O3
To select the IR MWs of O3 appropriate for the
retrieval, we check the spectral region which has
the larger variability according to a change of
concentration (vmr) (from 10 to 30 ) in the
troposphere and in the stratosphere using PROFFIT
2 (ground-based radiative transfer and
retrieval model)
UV-VIS main characteristics (07-28-08 at 11.00
am)
? grating spectrometer with optical fiber ?
silicon CCD array 2048 pixels ? Integration time
86 ms
Conclusions
1) 780-790 cm-1 2) 970-1150 cm-1 3) 2000-2140
cm-1 4) 2730-2820 cm-1 5) 3000-3100 cm-1

• The new experimental set-up is now fully
  operational at LISA Créteil.
• 2) We will use H2O and O3 to validate precision
  and accuracy of the new set-up.
• 3) Then we will validate satellite (IASI) and
  meteorological (ECMWF) H2O and O3 data.
• 4) We aim to improve knowledge of free
  tropospheric composition above Paris (VOCs)

References 1 C. Senten et alTechnical
Note New ground-Based FTIR measurements at Ile
de La Réunion observations, error analysis, and
comparisons with
independent data, Atmos. Chem. Phys.
Discuss. 8, 827-891, 2008
2 F. Hase et al Intercomparison of
retrieval codes used for the analysis of
high-resolution, ground-based FTIR measurements,
J. Quant. Spectrosc. Rad. Transf. 87, 25-52, 2004