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Degradation Monitoring

Degradation Monitoring. - IFE/DLR. Manfred W. Wuttke Envisat Calibration Review 9-13 September 2002 ESTEC, Noordwijk, The Netherlands. The Monitoring Concept.

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Degradation Monitoring

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  1. Degradation Monitoring - IFE/DLR Manfred W. Wuttke Envisat Calibration Review 9-13 September 2002 ESTEC, Noordwijk, The Netherlands

  2. The Monitoring Concept Monitoring the behaviour of SCIAMACHY in-orbit is an essential function during the Commissioning and Routine Operations Phase. It ensures that • the actual instrument status is known • countermeasures preventing instrument malfunctions can be initiated • data processing can incorporate the most up-to-date instrument characterisation

  3. Degradation Model (1/2) • Lightpath through instrument components is described as product of Müller matrices. • Assumption: Degradation of a component can be described as a linear factor on the corresponding Müller matrix.

  4. Degradation Model (2/2): Aging coefficients •  ASM •  ESM •  Diffuser •  Optical Bench Module to Science Detectors •  NDF •  Optical Bench Module to PMD 1-6 •  Optical Bench Module to PMD 7

  5. The m-factor concept(1/6) M-factors are used in the 0-1b processor to compensate for the radiometric degradation of SCIAMACHY. In general, a m-factor • is defined as a product of inverse aging coefficients and • can be determined as the ratio between a measured solar spectrum at the time t to a reference spectrum obtained for the same optical path at the time 0, i.e. BOL. Ideally, these reference spectra should be taken on-ground, but in practice this is not possible because measurements of the unobscured sun cannot be performed on-ground. Therefore, „earliest“ in-flight measurements shall be taken as reference.

  6. The m-factor concept (2/6) • mcal =1/ Calibration light path (via diffuser, NDF) to science detectors • mdl =1/  Limb light path to science detectors • mpl =1/  Limb light path to PMD detectors • mql =1/  Limb light path to 45° PMD detector • mdn =1/  Nadir light path to science detectors • mpn =1/  Nadir light path to PMD detectors • mqn =1/  Nadir light path to 45° PMD detector

  7. The m-factor concept(3/6) Strategy: • M-factors shall be computed on the basis of calibrated sun spectra • Calibration shall be consistent with operational L0-1b processing • Therefore tools are derived from Level 0-1b processor prototype software package

  8. The m-factor concept(4/6) Thus needed: • Continuous flow of sound Level 1b products: • To have consistent calibration data. • To monitor and extrapolate trends in instrument history • Up to date version of L0-1b processor prototype software package: • To apply consistently all corrections but the m-factors.

  9. The m-factor concept(5/6) Reference spectra have to be determined ASAP! Instrument seems to show signs of degradation already. The assumption m-factor = 1 @ “BOL“ is therefore questionable!

  10. The m-factor concept(6/6) For the ASM the aging coeffient  can be determined without reference to BOL. This will give a hint about at least the one assumption But: Calibrated spectra are needed!

  11. Conclusions(1/4) • We already see that the instrument is altering. • The basic idea of the m-factor concept, that the instrument didnt change between on ground characterization (keydata) and early inflight phase, is thus waning. • The Operational Long Term Monitoring concept depends on the level 1b product, which is not yet in a useful state (completeness, quality and supply of data).

  12. Conclusions(2/4) • Current monitoring activities thus depend heavily on • level 0 data, the supply of which is not guaranteed for long • tools for level 0 which were not foreseen to be used for • long term, • routine and • mass application.

  13. Conclusions(3/4) Under these circumstances • to get a comprehensive picture of the instrument status • as required to procure high quality data products • on adequate timescales is hard to achieve.

  14. Conclusions(4/4) • What is needed /missing: • Reliable data distribution • Sound Level 1b product • Up to date version pf L0-1 processor prototype package • What would (have) be(en) useful: • A more open policy concerning release of official software sources (extraction, calibration).

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