Institut für Umweltphysik/Fernerkundung Physik/Elektrotechnik Fachbereich 1 ENVIVAL-LIFE Meeting...

Institut für Umweltphysik/Fernerkundung Physik/ElektrotechnikFachbereich 1

ENVIVAL-LIFE Meeting 6/7 Dec 2010

S. Noël, K. Bramstedt, C. v. Savigny

IFE/IUP

SCIAMACHY Performanceafter the ENVISAT Orbit

Change


[email protected] ENVIVAL-LIFE Meeting 6/7 Dec 2010

ENVISAT Orbit Change• Required because original orbit is ‘booked’ for other missions

• New orbit: About 17 km lower, slightly shorter orbital period Drifting inclination and local time of equator crossing (about ± 10 min around

22:00 until 2013) New repeat cycle and cycle length of 30 days / 431 orbits

• Time for orbit change has been chosen to optimally use remaining fuel

• Schedule: First manoeuvre 22 October 2010 Most instruments switched off until 27 October 2010 Between 27 October and 2 November YSM instead of SYSM (reduced

pointing accuracy) Last orbit change manoeuvre 4 November 2010 Quasi-nominal service until end of 2010 (data to users with quality disclaimer) From January 2011 on everything nominal again



Impact on SCIAMACHY• SCIAMACHY operations had to be slightly adapted to new

orbit: Updated limb states:

• One horizontal scan less to guarantee limb-nadir matching

• Planned: Skip first tangent height (~3 km) and start at ~0 km

Updated timelines

• Some discussion about possible contamination before orbit change due to thrusters exhaust (but considered low risk at that time)

• Main performance checks after the orbit change: Thermal performance Geolocation performance (esp. limb and occultation measurements) Optical performance (throughput)



Temperatures• SCIAMACHY detector temperatures increased by about 0.5 K after the

orbit change

• Related to higher ENVISAT temperatures, caused by permanent use of KBS1 and KBS3 after Ka band antenna anomaly (not related to orbit change)

• ENVISAT temperatures will remain higher

• Adaptation of SCIAMACHY detector temperatures planned



Limb nadir matching

Limb nadir matching OK

Minor problem:Limb corner co-ordinates are flipped in L1b states ADS (NOT in measurement dataset!) due to removed limb level.

Red: Nadir state Green: Limb State Corners from states ADS

10 Oct 27 Oct



Limb THs in L1 product -1- Changes in limb state:

– Continuation of limb-nadir matching with changed orbit required modification

– One horizontal scan less (removal of -3 km scan).

General Scan Sequence:– General OK.– Step size OK.– Altitudes not changed?

Not OK!

Red : before mission extensionGreen : during mission extensionBased on L1b geolocation!



Limb THs in L1 product -2- TH first readout:

Still at ~-4.2 km

TH last readout(dark meas.)Moved from 263km → 269km

Note: NRT data, no AUX_FRAs!

Red : before mission extensionGreen : during mission extension

TH first readout

TH last readout (dark meas.)



Limb Geolocation: AUX_FRAs AUX_FRA files contain

attitude correction Orbit 45331

2010-Oct-31 no AUX_FRAs :

Geolocation as given in NRT product

with AUX_FRAs :Re-calculated with CFIs using AUX_FRAs

No larger change in tangent height.

→ AUX_FRAs will not correct for too low limb TH !

Lowest tangent altitude for each vertical profile (Up-down pattern is horizontal scan)



Accuracy of L1 Geolocation: Limb TH from TRUE version 1.8 retrievals

YSM

Method: – Determine tangent

height from UV ‘knee’

– Compare with L1 altitudes

Altitudes during YSM ~1.8 km too low

About zero offset in SYSM, also after orbit change.

OK!



Accuracy of L1 Geolocation: Solar Occultation TH: -Measure centre of sun-

Method: – Fit center of sun

from scans over solar disk

– Compare with TH in product

Altitudes during YSM ~3km too low, with large scatter.

Back to previous values with SYSM.

In line with state 47 analysis (jump of elevation mirror after switch to sun-follower)

OK!

Note: NRT data, no AUX_FRAs!

SYSMYSM



SCIAMACHY Degradation Monitoring

• Main method:– Ratio (calibrated) signal of well known source (sun above atmosphere, internal

white light source (WLS)) at time t to corresponding measurement at reference time t0

– Reference time for SCIAMACHY: 2 August 2002 (begin of nominal meas.)

– Performed for different light paths, corresponding to different viewing geometries

– Degradation correction factors (m-factors) are regularly produced and used in operational 1-2 processing (see: http://www.iup.uni-bremen.de/sciamachy/mfactors)

• Limitations:– No polarised light source available, therefore no monitoring of changing

polarisation sensitivity possible

– Scan angle dependent degradation correction in preparation



SCIAMACHY Light Path Monitoring

• The different SCIAMACHY light paths are regularly monitored using measurements of the unobscured sun above the atmosphere and the internal WLS



Throughput monitoring results (L1b / m-factors) General: Slightly enhanced variability during YSM period Throughput slightly affected by higher detector temperatures (caused

by higher ENVISAT temperatures) Limb light path:

– No significant effect. – Very slightly throughput loss in channel 2.

Calibration light path:– No significant effect.

Nadir light path:– Reduced signal for 27/28 Oct sub-solar (pointing mode) due to YSM

(excluded from operational m-factor calculation)– No signal for 27 Oct sub-solar (fast-sweep mode), due to blocking by

Ka-band antenna– Very slightly enhanced throughput for channel 3,4,5

Conclusion: No significant throughput changes.



Throughput monitoring (L1b / m-factors)

Orbit change



Summary• Limb states:

– Limb nadir matching: OK!– Limb sequence (with 30 levels) and stepping: OK!– Limb tangent height: First horizontal scan at -4 km, not ~0 km!

To be adapted in the near future– TRUE: ~-1.8 km TH offset during YSM period, later (SYSM) OK.

• Solar occultation TH/elevation angles:– Reduced performance during YSM (~-3km TH offset)– Back to nominal with SYSM (since 2 Nov 2010)

• Throughput monitoring:– No significant changes.

• Status of other instruments and platform: – No major problems– ENVISAT temperature increased due to permanent use of KBS1 &

KBS3 after Ka antenna anomaly



Backup slides



Throughput monitoring (L1b / m-factors) Nadir, ch. 1

Orbit change




Orbit change



Throughput monitoring (L1b / m-factors) Limb, ch. 1

Orbit change




Orbit change



Throughput monitoring (L1b / m-factors) Cal., ch. 1

Orbit change




Orbit change

Institut für Umweltphysik/Fernerkundung Physik/Elektrotechnik Fachbereich 1 ENVIVAL-LIFE Meeting...

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