doas retrievals of stratospheric o 3 and no 2 from odin / osiris limb-radiance measurements samuel...
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DOAS Retrievals of Stratospheric O3 and NO2 from Odin / OSIRIS Limb-Radiance
Measurements
Samuel BrohedeCraig S. Haley
and the Odin team
Chalmers University of Technology and York University
1st International UV/Vis Limb-Scattering workshop, Bremen, April 2003
OSIRIS onboard Odin
Odin
SMR OSIRIS
OS IRI
OSIRIS = Optical Spectrograph and InfraRed Imager System
SMR = Sub Millimeter Radiometer
1st International UV/Vis Limb-Scattering workshop, Bremen, April 2003
Odin orbit specifications
Polar orbiting Sun synchronous Near terminator 18.00 ascending node Altitude ~600 km Limb scanning between 7
and 70 km
1st International UV/Vis Limb-Scattering workshop, Bremen, April 2003
The Optical Spectrograph
Wavelengths: 280-800 nm (UV-Vis) Resolution: ~1 nm FOV: 1 km vertical, 40 km horizontal
OSIRIS
1st International UV/Vis Limb-Scattering workshop, Bremen, April 2003
OS spectra from one scan
O3 windowNO2 window
1st International UV/Vis Limb-Scattering workshop, Bremen, April 2003
DOAS analysis
Differential Optical Absorption Spectroscopy
Differential cross sections, ’, are used.
’
smoothed cross section
Smoothing: Polynomial or Boxcar
1st International UV/Vis Limb-Scattering workshop, Bremen, April 2003
Advantages of DOAS
Broad features like Mie and Rayleigh-scattering does not need to be modelled
No need to estimate real I0 / self calibrated
Multiple species can be measured simultaneously
High th spectrum (reference) used as I0
)()(),(
)(ln),('
'
0 thcthI
Ith
speciesiii
1st International UV/Vis Limb-Scattering workshop, Bremen, April 2003
DOAS windows
O3 windowNO2 window
1st International UV/Vis Limb-Scattering workshop, Bremen, April 2003
DOAS Least Squares Fit
2||)()(),('||min thcthspeciesi
ii
1st International UV/Vis Limb-Scattering workshop, Bremen, April 2003
The I0-effect
Structures in the reference spectrum (I0) .
Ratioing does not cancel out. Taking care of in the x-sections convolution.
resolutionhigh
nconvolutio *
)(
)()(),(
*
*
*
hr
I
Ith
hrs
hri
hrs
i
1st International UV/Vis Limb-Scattering workshop, Bremen, April 2003
The Ring effect
Filling in of Fraunhofer and Telluric lines Two approaches:
1 Backward modelling [ Sioris et al ]
2 Pseudo absorber [ Chance et al ] Including Ring corr. did not improve the fit.
1st International UV/Vis Limb-Scattering workshop, Bremen, April 2003
Polarization
Differential structures in response for perp. light
Included as a pseudo absorber in O3-window
1st International UV/Vis Limb-Scattering workshop, Bremen, April 2003
Tilt/Undersampling
Different tilt of reference and measured spectra + Fraunhofer structures + undersampling => ratioing won’t cancel out.
Included as a pseudo absorber in NO2-window
1st International UV/Vis Limb-Scattering workshop, Bremen, April 2003
T-dependent x-sections
Two possible approaches:
1) Use T at tangent height
2) Non linear fit for T
Only important for NO2-window
1st International UV/Vis Limb-Scattering workshop, Bremen, April 2003
Wavelength shift
Calibration differences between the OS and cross sections.
Taking care of in a non-linear fit
Only important in the NO2-window
No stretching/squeezing corrections
1st International UV/Vis Limb-Scattering workshop, Bremen, April 2003
Retrieval procedure
Effective column density, c(th) Vertical number density, n(z)[ molecules cm-2 ] [ molecules cm-3 ]
1st International UV/Vis Limb-Scattering workshop, Bremen, April 2003
Optimum Estimation (MAP)
A Priori climatology [ McLinden ] Non linear iteration RTM = LIMBTRAN pseudo-3D [ Griffoen ]
matrix covarianceerror
matrix covariance apriori
vectormodel forward
matrix functions weighting
profiledensity number priori a
S
S
F
nFK
n
)nK(n)F(n[c)SKS(KKSnn
a
a
aii1
εTiai
Tiai1i
1st International UV/Vis Limb-Scattering workshop, Bremen, April 2003
Calculating K and F
K and F are calculated numerically CPU-Time consuming calculations Two approaches:
1) 2- DOAS (ok for K in O3-window)
2) Sparse wavelength grid
1st International UV/Vis Limb-Scattering workshop, Bremen, April 2003
Method summary
O3-region NO2-region
Wavelengths: 571-617 nm 435-451 nm
Species: O3, NO2, O4 O3, NO2, O4
Corrections: I0, Pol I0, Tilt, T-dep, -shift
Ref. height: 50 km 50 km
Estimating K: 2- 2.5 nm step
Estimating F: 4 nm step 1 nm step
Alt range: ~15-40 km ~20-35 km
1st International UV/Vis Limb-Scattering workshop, Bremen, April 2003
O3-Results
1st International UV/Vis Limb-Scattering workshop, Bremen, April 2003
NO2-Results
1st International UV/Vis Limb-Scattering workshop, Bremen, April 2003
Off-plane orbit
1st International UV/Vis Limb-Scattering workshop, Bremen, April 2003
Ozone hole splitting
1st International UV/Vis Limb-Scattering workshop, Bremen, April 2003
Comparison
3 March 2002
OSIRIS:
lat:68.1o N
lon:10.6o W
17:23 UTC
POAM III:
lat:67.5o N
lon:20.5o W
18:27 UTC
1st International UV/Vis Limb-Scattering workshop, Bremen, April 2003
Comparison
8 Aug 2001
OSIRIS:
lat:76.9o N
lon:13.8o E
10:59 UTC
Sonde:
lat:78.9o N
lon:11.9o E
10:59 UTC
1st International UV/Vis Limb-Scattering workshop, Bremen, April 2003
Comparison
22 Aug 2001
OSIRIS:
lat:28.9o N
lon:16.1o W
18:48 UTC
Sonde:
lat:28.3o N
lon:16.5o W
11:17 UTC
1st International UV/Vis Limb-Scattering workshop, Bremen, April 2003
ComparisonPaired Radiances
DOAS
Percentage difference
Zonal
means
Nov 18
2001
1st International UV/Vis Limb-Scattering workshop, Bremen, April 2003
Comparison
Paired Radiances
DOAS
Percentage difference
Zonal
means
Nov 3
2002
1st International UV/Vis Limb-Scattering workshop, Bremen, April 2003
Conclusions and outlook
O3 compares well to Flittner and sondes
NO2 looks promising
Further validation needed Article soon submitted
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