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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).