Third International DOAS Workshop, Bremen, 20 - 22 March, 2006

Retrieval of BrO vertical distributions from Retrieval of BrO vertical distributions from SCIAMACHY limb measurements: SCIAMACHY limb measurements:

Data quality assessment and algorithmData quality assessment and algorithm improvementsimprovements

A. Rozanov1, J. P. Burrows1, S. Kühl2, C. McLinden3, K. Pfeilsticker2, J. Pukite2, R. Salawitch4, B.-M. Sinnhuber1,

C. Sioris5, T. Wagner2

1Instutute of Environmental Physics, University of Bremen, Germany2 Instutute of Environmental Physics, University of Heidelberg, Germany

3Meteorological Service of Canada, Toronto, Cananda4Jet Propulsion Laboratory, Pasadena, California, USA

5Harvard-Smithsonian Center for Astrophysics, Cambridge, USA

BOOST: A joint intercomparison projectBOOST: A joint intercomparison project

Bromine Oxide in the lOwer STratosphere (BOOST)Bromine Oxide in the lOwer STratosphere (BOOST)

Project objectivesProject objectives Comparison of BrO vertical distributions retrieved from SCIAMACHY

limb measurements using different retrieval algorithms

Investigation of possible reasons for the disagreement between the retrievals identified in previous studies

Improvement of the existing retrieval algorithms (especially the retrieval quality in the lower stratosphere and the upper troposphere)

Investigation of the sensitivity of the retrieved profiles to the retrieval parameters such as initial profiles, cross sections, spectral corrections

Participating retrieval groupsParticipating retrieval groups IUP, University of Bremen: Alexei Rozanov IUP, University of Heidelberg: Sven Kühl Harvard-Smithsonian Center for Astrophysics (SAO): Chris Sioris

Main inversion procedure:• Measurement vector: differential

signal in all spectral points at all selected tangent heights

• State vector: trace gas number densities at altitude levels

• Solution: Information Operator or Optimal Estimation

Retrieval algorithm of the University of BremenRetrieval algorithm of the University of Bremen

Simulated limb spectra Weighting functions w.r.t. concentrations

Forward modeling (SCIATRAN) :• Fully spherical treatment for SS• Approximation for MS

Measured and simulated limb spectra Vertically integrated WF

Correction parameters

Pre-processing (DOAS-like fit) at each tangent height:

•Shift and squeeze correction•Spectral corrections

Vertical distributions of trace gas number densities

Measured and simulated limb spectra with all corrections appliedWeighting functionsA priori constraints

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ratio

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Inversion procedure:• Measurement vector: difference

between measured and simulated slant columns

• State vector: trace gas number densities at altitude levels

• Solution: Optimal Estimation (maximum a posteriori)

Retrieval algorithm of the University of HeidelbergRetrieval algorithm of the University of HeidelbergO

ne it

erat

ion

only

Block Air Mass FactorsForward modeling (TRACY) :

•Fully spherical Monte Carlo

Measured limb spectra Cross sections

Slant columns as a function of tangent height

DOAS fit for both measured and simulated spectra at each tangent height:

•Shift•Spectral corrections

Vertical distributions of trace gas number densities

Slant columns Block Air Mass FactorsA priori constraints

Inversion procedure (Chahine-like):

Retrieval algorithm of SAORetrieval algorithm of SAO

Simulated limb spectra

Measured or simulated limb spectra Cross sections

Slant columns as a function of tangent height

DOAS fit for both measured and simulated spectra at each tangent height for a set of temperatures:

•No shift/squeeze correction•Spectral corrections

Vertical distributions of trace gas number densities

Measured slant columnsSimulated slant columns interpolated to an appropriate temperature

Forward modeling (VECTOR) :• Fully spherical treatment for SS• Approximation for MS

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Subsequent iterations:

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Retrieval settingsRetrieval settings

Uni BremenUni Bremen Uni HeidelbergUni Heidelberg SAOSAO

Spectral range 337 – 357 nm 337 – 357 nm 344 – 360 nm

Reference tangent height

~ 35 km ~ 35 km 33 – 70 kmco-addition

Spectral corrections

shift, 1/I0, tilt, eta, ring

shift, ring, 1/I0, /I0, I0-corrected O3 cross section, eta, zeta

tilt, I0-corrected O3 cross section

Temperature dependence

full O3 cross sections at 223 K and 243 K fitted

series of fits with O3 and NO2 cross sections at different temperatures

Regularizationweak statistical, smoothness

statistical sharp gradients are not permitted

Initial set of the limb states to be comparedInitial set of the limb states to be compared

Selection criteria (based on results from Selection criteria (based on results from Dorf at al., 2006):):

At the first stage of the project comparisons will be performed for the limb states collocated with selected balloon-borne DOAS measurements

For each balloon flight air mass trajectory calculations were done identifying the forward (being in the future w.r.t. the balloon flight) and the backward (being in the past w.r.t. the balloon flight) match with SCIAMACHY limb observations

List of selected balloon flights:List of selected balloon flights:

March 23rd, 2003; Kiruna (67.9oN, 21.1oE); 15:19 - 16:09

October 9th, 2003; Air sur l’Adour (43.7oN, 0.3oW); 15:39 - 17:09

March 24th, 2004; Kiruna (67.9oN, 21.1oE); 13:55 - 17:35

Stratospheric temperature at matching statesStratospheric temperature at matching states

Temperature dependence of BrO cross sectionsTemperature dependence of BrO cross sections

Convolved Fleischmann cross sections (FWHW = 0.2 nm) Convolved Fleischmann cross sections (FWHW = 0.2 nm)

Scaling factors Scaling factors (w.r.t 223 K)(w.r.t 223 K)

203 K 0.92

223 K 1.00

243 K 1.06

273 K 1.14

298 K 1.16

Cross sections comparison: Fleischmann vs. WilmouthCross sections comparison: Fleischmann vs. Wilmouth

Convolved cross sections Convolved cross sections (FWHM = 0.2 nm)(FWHM = 0.2 nm)

Absolute difference after Absolute difference after scaling, shift and squeezescaling, shift and squeeze

Scaling factors (Wimouth/Fleischmann): 1.03 @ 298 K, 1.11 @ 228/223 KScaling factors (Wimouth/Fleischmann): 1.03 @ 298 K, 1.11 @ 228/223 K

Relative shift: 0.004 – 0.006 nm @298 K 0.009 nm – 0.02 nm @ 228/223 KRelative shift: 0.004 – 0.006 nm @298 K 0.009 nm – 0.02 nm @ 228/223 K

Cross sections comparison: WahnerCross sections comparison: Wahner

Convolved cross sections Convolved cross sections (FWHM = 0.4 nm)(FWHM = 0.4 nm)

Convolved cross sections Convolved cross sections (Wahner fitted to Wilmouth)(Wahner fitted to Wilmouth)

Scaling factors (Wahner): 1.0 w.r.t Wilmouth, 0.9 w.r.t. Fleischmann Scaling factors (Wahner): 1.0 w.r.t Wilmouth, 0.9 w.r.t. Fleischmann

Shift (Wahner): 0.25 – 0.29 nm Wilmouth, 0.23 – 0.27 nm w.r.t. FleischmannShift (Wahner): 0.25 – 0.29 nm Wilmouth, 0.23 – 0.27 nm w.r.t. Fleischmann

Comparison between different retrievals (1)Comparison between different retrievals (1)

Balloon flight: Balloon flight: March 23rd, 2003; Kiruna (67.9oN, 21.1oE); 15:19 - 16:09

Backward match:Backward match: March 23rd, 2003; 11:07 UT; Orbit 5545; State 7; 41oN,16oE

Forward match:Forward match: March 24th, 2003; 9:01 UT; Orbit 5558; State 7; 56oN, 26oE

Comparison between different retrievals (2)Comparison between different retrievals (2)

Balloon flight: Balloon flight: October 9th, 2003; Air sur l’Adour (43.7oN, 0.3oW); 15:39 - 17:09

Backward match:Backward match: October 9th, 2003; 9:51 UT; Orbit 8407; State 9; 41oN,8oE

Forward match:Forward match: October 10th, 2003; 9:20 UT; Orbit 8421; State 9; 41oN, 16oE

Comparison between different retrievals (3)Comparison between different retrievals (3)

Balloon flight: Balloon flight: March 24th, 2004; Kiruna (67.9oN, 21.1oE); 13:55 - 17:35

Backward match:Backward match: March 24th, 2004; 10:36 UT; Orbit 10798; State 9; 66oN,9oE

Forward match:Forward match: March 25th, 2004; 8:25 UT; Orbit 10811; State 9; 62oN, 38oE

Dependence on a priori informationDependence on a priori information

Balloon flight: Balloon flight: October 9th, 200315:39 - 17:09Air sur l’Adour 43.7oN, 0.3oW

SCIAMACHY limb:SCIAMACHY limb: October 10th, 20039:20 UTOrbit 8421, State 941oN, 15oE

University of Bremen retrievals:University of Bremen retrievals:

Dependence on a priori informationDependence on a priori information

University of HeidelbergUniversity of Heidelberg SAOSAO

ConclusionsConclusions

All retrievals agree within error barsAll retrievals agree within error bars Error bars of SAO retrievals are very large in the lower layers: 60

% at 17 km increasing downwards, often > 100% below 16 km Retrievals of Uni Heidelberg result in slightly higher values compared

to Uni Bremen retrievals over the whole altitude range Below 20 km SAO retrieval tend to produce higher values as

compared to Bremen and Heidelberg results

Dependence on a priori informationDependence on a priori information Below 20 km Uni Heidelberg retrievals show a dependence on a priori

profiles Below 17 km Uni Bremen retrievals show a dependence on the form of

a priori profiles but not on the absolute values SAO retrievals are found to be independent of the initial profile

Effect of cross sections is estimated to be about 10%Effect of cross sections is estimated to be about 10%

OutlookOutlook

Additional comparisons are needed Additional comparisons are needed Additional DOAS flight: June 17th, 2005 Balloon-borne in-situ measurements with TRIPLE Balloon born SAOZ measurements

Model simulations and retrievalsModel simulations and retrievals SCIATRAN (Uni Bremen) VECTOR (SAO) TRACY (Uni Heidelberg)

Further investigation of the influence of the initialisation Further investigation of the influence of the initialisation parametersparameters