SCIAMCHY monitoring concept (basics) and results. J. Frerick, EOP-PVP. Layout. Motivation What could we learn from SCIAMACHY? Short tour through the SCIAMACHY instrument Commonalities Differences SCIAMACHY science channels SCIAMACHY PMD channels Monitoring concept Monitoring results
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SCIAMCHY monitoring concept (basics) and results
J. Frerick, EOP-PVP
Both instruments analyse the sun light, back scattered from the Earth atmosphere. But whereas GOME-II can observe in Nadir geometry only, SCIA can do Nadir and Limb (thanks to its so called Azimuth Scan Mirror ASM).
GOME-II detectors cover SCIA detectors 1-4.
Temperatures of SCIA detectors are a bit varying by channel.
In the VIS they appear to be even lower than GOME-II
SCIA:(-69 to -46 deg. C)
SCIA PMDs are only sensitive to p-polarized input.
Also their spectral resolution is different.
However, their thermal environment seems comparable (tbc).
Sun via Azimuth mirror and diffuser (on rear side of Elevation mirror)
IMPORTANT: ratios of different time series (e.g. sun-occultation/sun-sub-solar) yields information about degradation of single components, in this case the Azimuth mirror
In direct sun view (i.e. via mirrors), an aperture Stop (mechanism) is used to reduce the flux onto the detectors.
Ratio of dark blue (Sun via ASM mirror and ESM mirror) and
Light blue curve (sun via ESM mirror) yield the degradation of the ASM mirror.
As expected, the ASM mirror will show slower degradation rate, since it is used less frequent.
Result will be (eyeball) between the diffuser curve (green) and the ESM curve (light blue).
Although each light-path is monitored e2e, the major contribution – at least in the UV (and VIS/not shown yet) must be resulting from degradation of the mirror(s).
Channel 2 and PMD (A) degrade qualitatively the same and therefore confirm the conclusion from previous slide (i.e. that it is driven by degradation of the mirrors) – as part of the common light path.
Rates are already much lower than in the UV channel!
However, degradation of PMD’s seems slightly less. After 6 years,
Small differences to be noted, which could be artificial (tbc by SOST)
The science channel is a bit broader than the PMD, hence the ch2 average could be a bit wrong when compared to PMD.
Comparison of other science channel/PMDs looks similar.
The same monitoring information can also be displayed as a function of pixel/wavelength (might be easier for comparison with GOME-II results).
Even within a single channel, one can see clearly a 1/lambda dependency of the degradation. I.e. the shorter the wavelength, the stronger the effect.
However, the intra-channel degradation differences seem to get stronger with time.
Don’t get confused: The wavelength axis is upside down compared to channel 1 plots
Also, in channel 2, the degradation is stronger, the shorter the wavelength.
Average signal Channel 8
(T det. ~150 K!!!)
Exponential throughput loss (proportional to ice growing on detector)
Decontaminations unsuccessful – the ice came back, though it seemed to level of earlier (i.e. it is slowly leaving the system)
At a certain moment in time it was thought to be more efficient to stop decontamination and live with a reduced, but acceptable throughput.
Indirect by heating the radiant cooler…
Throughput monitoring only starts, once stable conditions are reached again! NO transient monitoring!!! (more details in SCIA handbook)
An important observation:
At the same time, the throughput goes down, the detector temperature increased (ice is warming up the detector / radiation effect).
GOME-II, though not having IR channels, might learn from this SCIA feature
degradation/ice growth rates could be compared
Detector temperature should be looked at, too.