saddu meeting, iup bremen, june 16/17, 2008 sciamachy limb pointing performance: 2002 – 2008 c....
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SADDU meeting, IUP Bremen, June 16/17, 2008
SCIAMACHY limb pointing performance: 2002 – 2008
C. von Savigny1, M. Gottwald2, E. Krieg2, K. Bramstedt1, S. Noël1, J. W. Kaiser3, A. Rozanov1, H. Bovensmann1, John P. Burrows1, and the
SCIAMACHY Quality Working Group
1 Institute of Environmental Physics, University of Bremen, Bremen, Germany 2 Deutsches Zentrum für Luft- und Raumfahrt (DLR), Wessling, Germany
3 European Centre for Medium-Range Weather Forecasts (ECMWF), Reading, UK
SADDU meeting, June 16/17, 2008IUP Bremen
SADDU meeting, IUP Bremen, June 16/17, 2008
Outline
Information on SCIAMACHY pointing errors / Envisat attitude errors
• „Knee“ retrievals using TRUE
• Results on Level 1 version 5.04 data
- Elevation/azimuth discontinuities occuring at sun aquisition during solar occultation (State 47 measurement)
- Sun position measurements in „sub-solar mode“ (State 53 measurements)
• Results on Level 1 version 6.03 data
SADDU meeting, IUP Bremen, June 16/17, 2008
TRUE = Tangent height Retrieval by UV-B Exploitation
• TRUE [Kaiser et al., 2004] exploits the maximum (”knee”) in the UV limb radiance profiles caused by the absorption in the Huggins- and Hartley-bands of O3.
• An optimal estimation (OE) scheme drives the RT model SCIARAYS [Kaiser, 2001]
• Tangent height weighting functions are calculated with the perturbation technique
• Field of view integration is considered (Gaussian FOV, FWHM = 2.8 km)
• Measured Limb spectra interpolated on 1 nm wavelength grid between 295 nm and 305 nm
• SCIAMACHY TH steps 11 – 15 used, i.e., tangent heights between ≈ 35 km and ≈ 50 km
0
20
40
60
80
10-6
10-5
10-4
10-3
10-2
10-1
750 nm
355 nm
305 nm
280 nm
Limb radiance [a.u.]
Ta
ng
en
t h
eig
ht
[km
]
“knee”
SADDU meeting, IUP Bremen, June 16/17, 2008
Current version of TRUE (1.7)
Technical features of TRUE (Vs 1.7):
• IUP dynamical O3 climatology [Lamsal et al., 2003] together with EP-TOMS and OMI Total ozone column data for each day and location
• Use of ECMWF background atmosphere data rather than the NASA climatology (NASA report 1292)
Quality of ECMWF O3 profiles in upper stratosphere and lower mesosphere not well established not usable for pointing retrievals
TRUE version O3 climatology P & T profiles Mean offset 2004 (L1 vs. 5.04)
1.4 UGAMP NASA ≈ 1.1 km
1.6 UGAMP ECMWF ≈ 1.7 km
1.7 IUP dymamic ECMWF ≈ 1.5 km
SADDU meeting, IUP Bremen, June 16/17, 2008
Sample fits
35 km
50 km
Measurements in blackModel in red
August 4, 2007
SADDU meeting, IUP Bremen, June 16/17, 2008
Monthly and tropical (20°S – 20°N) mean TH offsets
Mean value 06/2006 – 06/2007:0.27 ± 0.07 km
Level 1 vs. 6.02/6.02
Level 1 vs. 5.04
SADDU meeting, IUP Bremen, June 16/17, 2008
SCIAMACHY measurement sequence
Solar spectrum measure- ment in sub-solar geometry(state 53)
Sun-aquisition at TOA during solar occultation (state 47)
SADDU meeting, IUP Bremen, June 16/17, 2008
SF active
SF not yet active
mism
atchState 47 elevation discontinuities (Stefan Noël, IUP)
• Analysis is based on measurements during pointing phase above atmosphere within solar occultation (State ID 47)
• Lv0 data have been processed with CFI s/w
• Mispointing = LOS – PredictedSun (@BCPS=1055 = 2nd last readout)
SADDU meeting, IUP Bremen, June 16/17, 2008
Comparison of sun acquisition (state 47) and TRUE retrievals
TRUE vs. 1.7 State 47
TRUE State 47Offset: 0.99 km 1.51 kmAmplitude: 0.92 km 0.95 kmLinear trend: 16 m / month 22 m / month
Least-sqares-fit parameters:
SADDU meeting, IUP Bremen, June 16/17, 2008
• Observed Anomalies (LoS angle)
- Solar occultation: azimuth = 0.1 deg2 elevation = -0.04 deg3
jumps of the ASM and ESM readings when switching to Sun Follower (State 47)2 at 17.2 km3 at 100 km
- Subsolar: azimuth = 0.05 deg4 elevation = -0.02 deg
jump of the ESM readings when switching to Sun Follower and temporal shift of maximum signal (State 53)
- Limb: elevation = -0.016 deg1
‘SCIAMACHY is pointing too low tangent heights are too large’1 possibly larger (not considered for determination of misalignment correction)
Misalignment modeling I (Manfred Gottwald, DLR)
SADDU meeting, IUP Bremen, June 16/17, 2008
‘Modelling the Discontinuities’Assumption
- jumps, temporal shift in subsolar signal and limb BIAS are caused by extra misalignment
(known misalignment LoS: pitch = 0.00065°, roll = 0.00167°, yaw = - 0.22746°)
Misalignment budget
- pitch: pt = pi + pp + pe (t = total misalignment, i = instrument, p = platform, e = extra)
- roll: rt = ri + rp + re
- yaw: yt = yi + yp + ye
Misalignment modeling II
SADDU meeting, IUP Bremen, June 16/17, 2008
Derived extra misalignments
Total misalignment correction:AOCS = [pitch, roll, yaw]
Level 1 data vs 6.03: init.file version 4.05 with AOCS = [-0.0260°, -0.020°, -0.21846°]Level 1 data vs 6.02: init.file version 4.04 with AOCS = [-0.0196°,0.000°,-0.22746°]
Pitch misalignment Limb tangent height difference
19.6 mdeg ≈ 1.1 km
26 mdeg ≈ 1.45 km
Extra misalignment correction:
pitch: -0.0260°
roll: -0.020°
yaw: +0.009°
SADDU meeting, IUP Bremen, June 16/17, 2008
Mean TH offset (01/2004 – 04/2006): approximately 1.5 km
This is in very good agreement with:
• the extra pitch misalignment derived from solar occultation measurements by Gottwald et al. [2007] leading to limb TH error of about 1.45 km.
• stratospheric O3 profile validation results [Brinksma et al., 2005]
TRUE results (Level 1 data 5.04 and 6.01/02)
SADDU meeting, IUP Bremen, June 16/17, 2008
O3
z
West
East
1234
West – East variations of TH offsets
150 – 200 m
Indications for horizontally tilted scanning
SADDU meeting, IUP Bremen, June 16/17, 2008
East-West difference in TRUE TH offsets: ≈ 200 m
• no apparent change with 12/2003 orbit model update
• no pronounced seasonal variation
• increase since mid 2006 ?
This is in qualitative and good quantitative agreement with the roll misalignment derived from solar elevation jumps in sub-solar measurements:
Extra roll misalignment: -0.020° ± 0.001°
vertical shift for 480 km horiz. distance: ≈ 160 m
Also: qualitative agreement with O3 validation results for the 4 azimuthal segments [Lolkema et al., 2005]
Vertical shifts between adjacent O3 profiles: 150 – 200 m
for a horizontal distance of 240 km
Consistency of different results
TRUE, extra roll misalignment and O3 profile validation yield qualitatively consistent results. TRUE and roll misalignment also in good quantitative agreement.
SADDU meeting, IUP Bremen, June 16/17, 2008
TRUE results for Level 1 version 6.03
SADDU meeting, IUP Bremen, June 16/17, 2008
Long-term trends in tropical mean pointing offset ?
Apparent trend may have many reasons:
e.g., solar cycle variations of tropical, upper stratospheric O3
No final conclusions possible right now, but monitoring required
SADDU meeting, IUP Bremen, June 16/17, 2008
East – West difference in TRUE retrievals
East-West difference for L1 vs. 6.03 smaller due to extra roll-misalignment correction
SADDU meeting, IUP Bremen, June 16/17, 2008
Conclusions
• Absolute tangent height offset – pitch misalignment (L1 vs. 5.04):
1) Modelling of elevation/azimuth discontinuities [Gottwald et al.] about 1.45 km in limb
2) TRUE vs. 1.7 about 1.5 km (01/2004 – 04/2006)
3) O3 profile validation at low latitudes about 1.5 – 2 km offset at low latitudes At high latitudes inconsistent picture, particularly in NH
• Horizontally tilted scanning – roll misalignment (L1 vs. 5.04):
3 independent techniques show qualitatively (i.e. in terms of sign) consistent results:
1) O3 profile validation [Lolkema et al.]: about 300 – 400 m East-West difference*
2) TRUE: about 200 m East-West difference
3) Modelling of Sub-solar elevation jumps [Gottwald et al.]: about 160 m East-West difference
• TRUE TH offsets for L1 vs. 6.03 much smaller than for vs. 5.04. Remaining variations (seasonal, long-term) need to be investigated further
*Vertical East-West difference for 480 km horizontal distance