doas retrievals of stratospheric o 3 and no 2 from odin / osiris limb-radiance measurements samuel...

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


Odin orbit specifications

Polar orbiting Sun synchronous Near terminator 18.00 ascending node Altitude ~600 km Limb scanning between 7

and 70 km


The Optical Spectrograph

Wavelengths: 280-800 nm (UV-Vis) Resolution: ~1 nm FOV: 1 km vertical, 40 km horizontal

OSIRIS


OS spectra from one scan

O3 windowNO2 window


DOAS analysis

Differential Optical Absorption Spectroscopy

Differential cross sections, ’, are used.

’

smoothed cross section

Smoothing: Polynomial or Boxcar


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


DOAS windows

O3 windowNO2 window


DOAS Least Squares Fit

2||)()(),('||min thcthspeciesi

ii


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


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.


Polarization

Differential structures in response for perp. light

Included as a pseudo absorber in O3-window


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


T-dependent x-sections

Two possible approaches:

1) Use T at tangent height

2) Non linear fit for T

Only important for NO2-window


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


Retrieval procedure

Effective column density, c(th) Vertical number density, n(z)[ molecules cm-2 ] [ molecules cm-3 ]


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


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


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


O3-Results


NO2-Results


Off-plane orbit


Ozone hole splitting


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


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


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


ComparisonPaired Radiances

DOAS

Percentage difference

Zonal

means

Nov 18

2001


Comparison

Paired Radiances

DOAS

Percentage difference

Zonal

means

Nov 3

2002


Conclusions and outlook

O3 compares well to Flittner and sondes

NO2 looks promising

Further validation needed Article soon submitted

doas retrievals of stratospheric o 3 and no 2 from odin / osiris limb-radiance measurements samuel...

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