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Page 1Sciamachy Validation Workshop – Bremen - 6-8 December 2004
Contribution to the validation of SCIAMACHY scientific data products for
CO, CH4, CO2 and N2O total column amounts using ground-based FTIR
network data.
M. De Mazière, B. Dils, M. Buchwitz, R. De Beek, C. Frankenberg, A. Gloudemans, H. Schrijver, M. van den
Broek et al.
Belgian Institute for Space Aeronomy, Ringlaan 3, B-1180 Brussels, Belgium,
Page 2Sciamachy Validation Workshop – Bremen - 6-8 December 2004
Coworkers
at BIRA-IASB
J. GranvilleP. GérardT. Jacobs
J.C. LambertC. Vigouroux
J. Notholt, T. WarnekeInstitute of Environmental Physics, University of Bremen, Germany
T. Blumenstock, S. MikuteitForschungszentrum Karlsruhe, IMK, Germany
E. Mahieu, P. Demoulin, P. DuchateletInstitut d'Astrophysique et de Géophysique, University of Liège, Belgium
J. Mellqvist, A. Strandberg Chalmers University of Technology, Sweden
R. Sussmann, W. StremmeForschungszentrum Karlsruhe, IFU, Germany
H. Fast, R. L. Mittermeier Meteorological Service of Canada (MSC)
T. Kerzenmacher, K. Strong, J.Taylor, A.Wiacek University of Toronto, Canada
S. Wood, D. Smale National Institute for Water and Air Research (NIWA), New-Zealand
D. Griffith, N. JonesUniversity of Wollongong, Australia
C. Rinsland NASA Langley Research Center, USA
Contributing PI’s
Page 3Sciamachy Validation Workshop – Bremen - 6-8 December 2004
Correlative datasetStation Lat N Lon E Alt(m)
NY.ALESUND 78,91 11,88 20
KIRUNA 67,8 20,4 419
HARESTUA 60,22 10,75 580
ZUGSPITZE 47,4 11,1 2964
JUNGFRAUJOCH 46,55 7,98 3580
EGBERT 44,23 -79,78 251
TORONTO 43,7 -79,4 174
IZANA 28 -16 2367
WOLLONGONG -34,45 150,88 30
LAUDER -45,05 169,68 370
ARRIVAL.HEIGHTS -77,85 166,78 190
Page 4Sciamachy Validation Workshop – Bremen - 6-8 December 2004
SCIAMACHY retrieval methods
WFM-DOAS: Weighting Function Modified DOASChannel 8Two windows: CH4 + N2O → 2265.0 – 2280.0 nmCO → 2359.0 – 2370.0 nmCO2 → 1558.0 – 1594.0 nm (channel 6)
IMLM : Iterative Maximum likelihood MethodChannel 8: 2354.00 – 2370.45 nmCH4 and CO from the same window
IMAP : Interactive Maximum A Posteriori-DOASCH4 from channel 6CO from channel 8: 2324.2 – 2334.9 nm
Page 5Sciamachy Validation Workshop – Bremen - 6-8 December 2004
Comparison remarks(FT)IR is the only GB technique to provide correlative total column data –
but number of GB measurements is limited - cf. need clear sky
Comparisons between total column data at high altitude stations;adopted approach: to use altitude-normalised data which is a better compromise for CH4
and N2O than for CO* still in mountainous regions, pixels do not represent uniform elevation
Comparisons at stations situated near the coast (e.g. Wollongong) - cf colocated pixels may be over sea Verify whether SCIA data are over land
Page 6Sciamachy Validation Workshop – Bremen - 6-8 December 2004
Maximizing Data overlap
Maximizing data overlap:
→ polynomial fit through GB data
But no extrapolation!
*Good representation of seasonal variability
(average std= 1-2%, except CO, 10%)
*Loss of information on certain possible short term events
Page 7Sciamachy Validation Workshop – Bremen - 6-8 December 2004
Selection criteria
Data processed for two grids around the GB stations:
Large grid = Lat ± 2.5°
Lon ± 10°
Small grid = Lat ± 2.5°
Lon ± 5°
Sciamachy data cover the jan → okt/nov time periodExcept CH4-IMAP: aug-nov
Page 8Sciamachy Validation Workshop – Bremen - 6-8 December 2004
Data overlap
Global time series for WFMDOAS and GB CO and CH4
(no additional filtering, fixed offset/station, + = GB data)
Large data loss when restricted to point-to-point comparison
Page 9Sciamachy Validation Workshop – Bremen - 6-8 December 2004
Additional Selection criteria
WFM-DOAS: Cloud-free, Over land (altitude > 0), Solar Zenith Angle < 85 deg, Error (fitting) <10% for CH4 and CO2 , < 60% for CO and N2O
IMLM-SRON: Cloud-free, Albedo >=0.01, Error (instrumental) < 2E18 for CH4 (~7%) and <1.5E18 for CO (~70%)
IMAP: No further selection needed for CH4, variance of the fit residual (without weighting) < 0.017, with weighting between 10 and 0.1, error < 7E17 and 30% for CO
Note: Several selection criteria have already been applied to the starting dataset
Page 14Sciamachy Validation Workshop – Bremen - 6-8 December 2004
CO
Retrieval algorithm
Average Bias over all stations and time (small grid)
Average Bias over all stations and time (large grid)
WFM-DOAS (24.56 ± 33.22)%
(21.76 ± 30.05)%
IMLM-SRON* (-3.51 ± 82.51)% (-1.56 ± 83.60)%
IMAP (-21.86 ± 27.58)%
(-19.14 ± 26.36)%
Std GB-FTIR 10.56%
*IMLM-SRON data is preliminary dataset!→ further improvement of std likely
Bias = mean (SCIA-polyfitFTIR)/polyfitFTIR
Page 15Sciamachy Validation Workshop – Bremen - 6-8 December 2004
CH4
Retrieval algorithm
Average Bias over all stations and time (small grid)
Average Bias over all stations and time (large grid)
WFM-DOAS v4.1 (-1.70 ± 7.93)% (-1.75 ± 7.34)%
IMLM-SRON* (-2.59 ± 15.83)%
(-3.68 ± 18.39)%
IMAP (-4.23 ± 3.54)% (-5.22 ± 4.04)%
Std GB-FTIR 2.09%
*IMLM-SRON data is preliminary dataset!→ further improvement of std likely
Page 16Sciamachy Validation Workshop – Bremen - 6-8 December 2004
Latitude dependence?
CH4_bias as a function of latitude
-14-12-10-8-6-4-202468
-90 -40 10 60
Lat (deg)
Bia
s (%
) WFMDOAS
SRON
IMAP
CH4_bias as a function of latitude
-30
-20
-10
0
10
20
30
-90 -40 10 60
Lat (deg)
Bia
s (%
) WFMDOAS
SRON
IMAP
CO-bias as a function of latitude
-60
-40
-20
0
20
40
60
80
100
120
-90 -40 10 60
Lat (deg)
Bia
s (%
) WFMDOAS
SRON
IMAP
CO-bias as a function of latitude
-60
-40
-20
0
20
40
60
80
100
120
-90 -40 10 60
Lat (deg)
Bia
s (%
) WFMDOAS
SRON
IMAP
Page 17Sciamachy Validation Workshop – Bremen - 6-8 December 2004
CO2 + N2O
Retrieval algorithm
Average Bias over all stations and time (small grid)
Average Bias over all stations and time (large grid)
WFM-DOAS CO2 (-11.06 ± 7.42)%
(-11.39 ± 6.64)%
Std GB-FTIR CO2 1.06%
WFM-DOAS N2O (-1.10 ± 26.83)%
(-0.34 ± 26.60)%
Std GB-FTIR N2O 1.75%
Page 18Sciamachy Validation Workshop – Bremen - 6-8 December 2004
Remarks
No information on the time dependence of the bias! Of major importance in determining the accuracy of the
retrieval model, is assessing whether or not the SCIA data ‘follows’ the GB data over time.
No data averaging was performed
Outliner detection and removal (criteria?)
All algorithms, IMLM (correction for dark current over orbits) and IMAP (implementation of the cloud retrieval utility for CO), undergo continuous improvements.
Page 19Sciamachy Validation Workshop – Bremen - 6-8 December 2004
Future work
In depth analysis of the time/lat dependence of the bias
Comparing daily/ weekly/ monthly averages of SCIA and FTIR data
Further investigation of various selection criteria
Comparisons between Ground Based data and Theoretical Models