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UV-VISIBLE Spectrometers DOBSON and SAOZ. Andrea Pazmiño and Alain Sarkissian LATMOS, Institut Pierre Simon Laplace, CNRS-UVSQ-UPMC, Paris, France Outline History The Dobson The SAOZ. Measurement of minor atmospheric constituents Beer-Lambert Law: I = I 0 . e - - PowerPoint PPT Presentation
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UV-VISIBLE SpectrometersDOBSON and SAOZ
Andrea Pazmiño and Alain SarkissianLATMOS, Institut Pierre Simon Laplace, CNRS-UVSQ-UPMC, Paris, France
Outline• History• The Dobson• The SAOZ
Measurement ofminor atmospheric constituents
Beer-Lambert Law:I = I0 . e -
= -ln(I/I0)
and
= .NL + Ray + Mie
: absorption cross sectionNL : number of molecules in the line-of-sight
N
L
HistoryRegular measurements of ground ozone concentration at Montsouris Park (Albert Lévy)
1877-1907
1979 First measurements from orbit by TOMS
1985 Discovery of the ozone hole (in Antarctica)
OCTOBER
Measurements of ozone by Dobson
at Faraday, Antarctica
1988 First measurement of ozone by SAOZ (Dumont d'Urville, Antarctica) in the frame of the Montreal Protocol (1987)
1924 Dobson develop an ultraviolet spectrograph to measure the integrated ozone (column)
Earth
stratosphere
Measurement ofminor atmospheric constituents
If Nv correspond to the vertical column of constituent x:
Nvx = NLx(SZA,) / AMFx(SZA,)
AMF = Air Mass Factor
Nv
Measurement of atmospheric minor constituentsby UV-visible spectrometry
I / I0 = e -
Beer-Lambert law: = log(I0/I) = . N
Absorption cross sectionN Number of molecules in the line-of-sight
Planet
Satellite
Atmospheric layer
OrbitStar or Sun or Moon
2
1
23
Ground-Based
Spectrometers
Dispersive object
Photodetector
Entrance slit
Output slit
Passive remote sensing and not destructive methodDecomposition of light radiation following → analysis of the spectral distributionCharacterized by its resolution (ability to separate two very close wavelengths)
►
►
►
Dobson and SAOZ spectrometers
DOAS technique (relative) O3, NO2, OClO, PSC Zenith-sky measurements at twilight Measurements in the Visible (Chappuis band)
• Measurements in polar regions in winter • Measurements in all weather conditions• Completely automatic• 20 instruments• >20 years of measurements in Antarctica
Differential absorption (absolute)
O3
Direct Sun measurements Measurements in the Ultraviolet (Huggins band)
• No measurements during polar winter• No measurements in bad weather• Automatic and/or manual• More than 80 instruments• Long series (80 years in Arosa)
Dobson spectrometer
Dobson Measurements
I / I0 = e -
Generally, direct Sun measurements
→ AMF = 1 / cos (SZA)
The Dobson spectrometer uses 2 pairs of wavelengths
= . NL → = . NL
where
= diff. Mie scattering contribution + ( . NL ) O3
O3
Pairs of wavelengths used by Dobson spectrometer
Pair (nm)A 305.5 – 325.4B 308.8 – 329.1C 311.4 – 332.4D 317.6 – 339.8C' 332.4 – 453.6
• Double pairs AD: most reliable for direct Sun measurements → standard
• Double pairs CD: large optical path
O3 = f(T)
Dobson networkFioletov et al., 2008
Dobson measurements: trends
Dobson
Arosa, Switzerland since 1926
Year
Ozo
ne
[DU
]
Conclusion: Dobson► ground-based measurements► direct Sun measurements (generally), or at zenith-sky► measurements in the UV (Huggins band for O3)► uses pairs of wavelengths► differential absorption► simple geometry (AMF = 1/cos(SZA) for direct sun
measurements)==> ++ and --++ good accuracy (< 1-2 %)++ systematic comparison between instruments (calibration)++ 80 instruments++ very long series
-- not in winter at polar regions-- not when bad weather-- needs operator
-- needs correction of absorption cross section of ozone in the UV from temperature
SAOZ spectrometerSystème d’Analyse par Observation Zenithale
Outside Inside
SAOZ Interface
PC
SAOZ
SAOZ spectrometer
ARGOS
shutter, grating, detector
Electronic device
GPS antenna
• Zenith-sky viewing• Twilight geometry• High sensitivity
to the stratosphere (~200 km)
Vertical column calculation:
0SCD RVAMF
O3
SAOZ spectrometer
Slant column Residual amount in reference spectrum
Air mass factor
Comparison of spectrum to the reference spectrum re-adjust the spectrum in wavelength
I/Io
I=Io * e –
Beer-Lambert Law
Signal(I)
Reference (Io)
45°
Flux
(x10
3 arb
itrar
y un
its)
Wavelength (nm)
SAOZ spectrometer Spectral Analysis
Application of high pass filter
NL
= -ln(I/Io)
NO2O3
To suppress attenuations of lower frequency
(Rayleigh and Mie)1)
Least mean square correlation => NL (measured slant column)
2)
SAOZ spectrometer Spectral Analysis
Optical Thickness
Absorption cross-section
O4 H2O
SAOZ spectrometer Differential Spectral Analysis
NO2O3
0.0200.0150.0100.005
0-0.005-0.010-0.015-0.020-0.025-0.030
residual – NL < 1/1000
Residual Differential Spectrum
ii NLi
NLO3= O3 /O3
200
150
100
50
0
Sla
nt c
olum
n (x
1018
mol
/cm
2)
9080706050
SZA
O3
86°<SZA<91°
SAOZ spectrometer
400
380
360
340
320
300
280
260
Ver
tical
col
umn
(Dob
son)
252015105
AMF
O3 320 DU
86°<SZA<91°
Col
onne
Ver
tical
e (D
U)
Col
onne
obl
ique
(x10
18 m
ol./c
m2 )
Standards SAOZ data : daily vertical columns of O3 and NO2 at twilight
VO3= NLO3+R0/AMFO3
SAOZ networkNy-Alesund
SalekhardZhiganskSodankyla
HarestuaAberystwyth Jungfrau
OHP
Tarawa
Bauru
Rio Gallegos
Reunion
Kerguelen
Rothera
ConcordiaDumont d’Urville
Scoresbysund
Thule
Long term series at Dumont d’UrvilleSAOZ
Ozon
e (D
U)NO
2 (x1
015
mol
/cm
2 )
TOMS : -0,6% SCIA : -0,3% GOME : 0,5% OMI (TOMS) : -1.3% OMI (DOAS) : 0%
Differences
Monthly Mean
Col
onne
ver
tical
e d’
ozon
e (D
U)
(Sat
ellit
e-S
AO
Z)/S
AO
Z (%
)
Comparison with satellites at OHP
SAOZ
Ozone loss: methodology
Comparison of passive O3 of models with SAOZ measurements O3 : accumulated ozone loss2 models : REPROBUS & SLIMCAT
SAOZZhigansk
(CNRS/CAO)
Salekhard(CNRS/CAO)
Sodankyla(CNRS/FMI)
Harestua(BIRA)
NyAlesund(NILU)
Thule (DMI)
ScoresbySund(CNRS/DMI)
Eureka(CNRS/UoT)
Zhigansk(CNRS/CAO)
Salekhard(CNRS/CAO)
Sodankyla(CNRS/FMI)
Harestua(BIRA)
NyAlesund(NILU)
Thule (DMI)
ScoresbySund(CNRS/DMI)
Zhigansk(CNRS/CAO)
Salekhard(CNRS/CAO)
Sodankyla(CNRS/FMI)
Harestua(BIRA)
NyAlesund(NILU)
Thule (DMI)
ScoresbySund(CNRS/DMI)
Zhigansk(CNRS/CAO)
Salekhard(CNRS/CAO)
Sodankyla(CNRS/FMI)
Harestua(BIRA)
NyAlesund(NILU)
Thule (DMI)
ScoresbySund(CNRS/DMI)
Eureka(CNRS/UoT)
Sensibility of O3 loss to history of stratospheric temperature=> high annual variability
Warm winters: 5-13% or 25-60 DU (eg. 1998/99, ) Cold winters: 20-30% or 90-140 DU (eg. 2007/08, )
Arctic ozone loss
SAOZ
- ground-based measurements- zenith-sky measurements at twilight- ozone measured in the visible Chappuis band- differential absorption- complicated geometry (AMF = f(SZA,))
++ good accuracy (<3% for ozone)++ >20 years series in polar regions++ measurements in polar regions in winter when ozone hole forms++ completely automatic++ measurements in all weather conditions++ simultaneously measurements of NO2, OClO, BrO and PSC detection
-- needs radiative transfer calculation (AMF)-- sensible to vertical profiles that generates seasonal variation
SAOZ data of O3 & NO2 in real time (current year) & consolidate (already validated by the Principal Scientist and sent to NDACC) :
- http://saoz.obs.uvsq.fr/SAOZ-RT.html
- http://saoz.obs.uvsq.fr/SAOZ_consol_v2.html
Conclusions: SAOZ