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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. RayLaboratoire 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.
ABSTRACTGround-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 H 2O, 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.
Experimental setup Instrumental Line Shape
set of micro-windows in IR for O3
References : [1] C. Senten et al;Technical 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
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 1901100 nm.
To select the IR MW’s 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)
First Results
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
Conclusions
FTIR
Solar tracker
Motorised dome rotationSet up
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)
FWHM = 0.06 cm-1
UV-VIS : main characteristics (07-28-08 at 11.00 am)
2040 2070 2100 2130 2160 2190 2220 2250
1.45
1.50
1.55
1.60
1.65
1.70
1.75
sig
na
l
wavenumber (cm-1)
CO
grating spectrometer with optical fiber silicon CCD array 2048 pixels Integration time 86 ms
2150.88 2150.96 2151.04 2151.12 2151.20 2151.28 2151.36
1.46
1.48
1.50
1.52
1.54
1.56
1.58
1.60
1.62
1.64
1.66
sig
nal
wavenumber (cm-1)
CO
6400 6600 6800 7000 7200 7400 7600 7800 8000
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
sig
nal
wavenumber (cm-1)
CH4
2046 2048 2050 2052 2054 2056 2058 2060 2062-0.02
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
sig
na
l
wavenumber (cm-1)
CO
2740 2750 2760 2770 2780 2790 2800 2810 2820 2830
0.00
0.05
0.10
0.15
0.20
0.25
0.30
sig
na
l
wavenumber (cm-1)
N2O
3110 3120 3130 3140 3150 3160 3170 3180 3190
0.00
0.05
0.10
0.15
0.20
0.25
sig
nal
wavenumber (cm-1)
H2O
4760 4780 4800 4820 4840 4860 4880 4900 4920-0.05
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
sig
na
l
wavenumber (cm-1)
CO2
780 782 784 786 788 7902750000
2800000
2850000
2900000
2950000
3000000
3050000
3100000
3150000
sig
na
l
wavenumber (cm-1)
MW 1
960 980 1000 1020 1040 1060 1080 1100 1120 1140 1160
0
2000000
4000000
6000000
8000000
10000000
sig
na
l
wavenumber (cm-1)
MW 2
1980 2000 2020 2040 2060 2080 2100 2120 2140 2160
8000000
10000000
12000000
14000000
16000000
18000000
20000000
22000000
sig
na
l
wavenumber (cm-1)
MW 3
2720 2730 2740 2750 2760 2770 2780 2790 2800 2810 2820 2830
25000000
26000000
27000000
28000000
29000000
30000000
31000000
sig
na
l
wavenumber (cm-1)
MW 4
2990 3000 3010 3020 3030 3040 3050 3060 3070 3080 3090 3100 3110
24000000
26000000
28000000
30000000
32000000
34000000
36000000
sig
na
l
wavenumber (cm-1)
MW 5
800 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800 3000
0
7000000
14000000
21000000
28000000
35000000
sig
na
l
wavenumber (cm-1)
MW 1 MW 2 MW 3 MW 4 MW 5
300 400 500 600 700 800 900 10000
2000
4000
6000
8000
10000
12000
14000
16000
18000
sig
na
l
wavelength (nm)
Band A of O2
2000 4000 6000 8000 10000 12000 14000
0.0
0.1
0.2
0.3
0.4
tra
nsm
issi
on
wavenumber (cm-1)
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