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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
Degradation Monitoring


Manfred W. Wuttke

Envisat Calibration Review

9-13 September 2002

ESTEC, Noordwijk, The Netherlands

The monitoring concept
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

Degradation model 1 2
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.

Degradation model 2 2 aging coefficients
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

The m factor concept 1 6
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.

The m factor concept 2 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

The m factor concept 3 6
The m-factor concept(3/6)


  • 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

The m factor concept 4 6
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.

The m factor concept 5 6
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!

The m factor concept 6 6
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!

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).

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.

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.

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).