SCIAMACHY Long Term Monitoring
Health and performance of the SCIAMACHY instrument are regularly monitored by the Sciamachy Operations Support Team (SOST).Monitoring activities are essential to detect and possibly correct for the degradation of instrument components. Therefore long-term monitoring is a prerequisite for a high data product quality throughout the lifetime of SCIAMACHY.
One part of the long-term monitoring activities is the trend analysis of measurements with the internal White Light Source (WLS) and of observations of the unobscured Sun above the atmosphere. In order to monitor the different SCIAMACHY light paths solar measurements are taken in various viewing geometries: In limb/occultation geometry (via ASM and ESM mirrors), in nadir geometry (via the ESM mirror through the subsolar port), and via the so-called calibration light path involving the ASM mirror and the ESM diffuser.
SCIAMACHY long-term monitoring comprises a regular analysis of these measurements.
The plots displayed on this page show first results of these
monitoring activities.
Note that the monitoring data presented here have been reprocessed using
actual (Level 1b V6.x upwards) radiometric key data.
The displayed data have been produced in the following way:
All measured spectra have been divided by the corresponding measurement at a
reference time; then for each channel a median of the ratio is computed,
yielding an effective instrument throughput for the different light paths.
The reference spectra for all light paths are derived from measurements on 16
January 2003 (the time of the first monthly calibration performed with final
flight settings).
The resulting medians are then scaled to be 1 just after the first decontamination
under (quasi-)nominal measurement conditions in August 2002.
Therefore, the reference date for all data is in fact 2 August 2002.
Subsolar measurements before 30 November 2002 (about orbit 3922) did not
consider the known yaw misalignment of SCIAMACHY on ENVISAT and thus may
not be used for monitoring purposes.
Therefore there are no subsolar data shown before December 2002.
Since no valid subsolar measurements are available for August 2002 the subsolar
throughput data have been scaled to 2 August 2002 by using the same factor as for the
limb light path.
Note that measurements performed during times of reduced instrument
performance (e.g. switch-offs or decontamination periods) have been
omitted.
The plots are updated on a daily basis, thus reflecting the current status of the instrument.
Monthly long-term
monitoring plots are also available (click here).
PMD monitoring results can be
found here.
Spectrally resolved
throughput monitoring results (based on Level 0 data) can be found here.
Channel 1 (Click to Enlarge) 
|
Channel 2 (Click to Enlarge) 
|
Channel 3 (Click to Enlarge) 
|
Channel 4 (Click to Enlarge) 
|
Channel 5 (Click to Enlarge) 
|
Channel 6 (Click to Enlarge) 
|
Channel 7 (Click to Enlarge) 
|
Channel 8 (Click to Enlarge) 
|
As can be seen from the plots, the SCIAMACHY instrument is generally in good shape. However, to avoid misunderstanding, some features in the plots require additional explanation:
- General remark:
The results presented here are based on the analysis of uncalibrated (Level 0) data, which have been corrected for dead/bad pixels, dark current, scan angle dependencies, quantum efficiency changes, and the seasonally varying distance to the Sun. Additional calibration steps have not been performed, like for example a straylight correction. Therefore, variations smaller than about 1% require careful investigation. - Between 21 and 27 February 2003 the detector temperature settings have been slightly changed. This explains small jumps in the average signals at about orbit 5140 (especially visible in channel 1 for subsolar measurements).
- The WLS has proven to be radiometrically very stable except for a degradation in the UV which is correlated with the burn time.
- In the UV (channels 1 and 2) a small degradation is visible for all light paths. However, this degradation is much smaller than expected from e.g. GOME experience.
- Most prominent are the large throughput changes in the IR channels 7 and 8. The decrease in throughput is caused by growing ice layers on the detectors. The ice can be removed by heating during a decontamination procedure such that the full throughput is restored, but then the ice layers start to grow again.
- Variations of the measured average solar signal are often correlated with solar activity. Especially, this can be seen in the "Sun via ASM Mirror and ESM Mirror" data, which have the best temporal resolution.
- The (end of the) partial solar eclipse of 31 July 2003 shows up
in the
monitoring plots as a slight decrease of the "Sun via ASM Mirror and
ESM
Mirror" signal. This signal drop is not visible in the other data,
because there were no
corresponding measurements for the other light paths at the time of
the eclipse.
A similar (but larger) effect is visible during the partial solar eclipse of 14 October 2004. - The "Sun via ASM Mirror and ESM Mirror" data for 9 and 10
December 2003
are affected by the reduced ENVISAT pointing performance during this
time.
-
Until October 2006 the nadir/subsolar light path was monitored based on fast
sweep measurements.
However, subsolar pointing measurements are considered to have a better quality
for monitoring purposes (especially for PMD monitoring) and thus shall become the
new baseline.
Since 1 October 2006 subsolar measurements in fast sweep scan mode are only executed once per month (before that time: daily) whereas subsolar measurements in pointing mode are executed twice per week (before: once per month).
Contact:
Stefan Noël (stefan.noel@iup.physik.uni-bremen.de)
Data Privacy
©2018