instrument monitoring and calibration two years after...

Institut für Umweltphysik/Fernerkundung Physik/ElektrotechnikFachbereich 1

Instrument Monitoring and Calibration Two Yearsafter Launch

M. W. Wuttke*, S. Noël*, J. Skupin, K. Gerilowski,H. Bovensmann, J. P. Burrows

Institute of Environmental Physics and Remote SensingUniversity Bremen FB 1

* SCIAMACHY Operations Support TeamSOST-ife

SCIAMACHY inflight calibration issues:

Institut für Umweltphysik/Fernerkundung Physik/ElektrotechnikFachbereich 1Overview

• SCIAMACHY instrument: characteristics and capabilities

• Examples of Scientific Results

• Monitoring concept

• Status of the instrument: monitoring results

• Radiometric calibration

• Summary

Institut für Umweltphysik/Fernerkundung Physik/ElektrotechnikFachbereich 1SCanning Imaging Absorption spectroMeter

for Atmospheric CHartographY

•Combination of Prism and 8 high resolution channels (each having its own grating)

•Spectral range from 214 to 2380 nm

•Spectral resolution from 0.2 to 1.5 nm

•7 broadband polarization measurement devices PMDs

•On-board calibration H/W

Scanners Prism

Channel 1

Channel 2

1

Channel 8

Channel 7

Channel 6

Channel 5

Channel 4

Channel 3

2 3 4 5 6 45

Polarization Measurement Devices (PMD)

WLS SLS

Atmosphere

Science channels

Sun

Institut für Umweltphysik/Fernerkundung Physik/ElektrotechnikFachbereich 1SCIAMACHY Instrument (1/2)

Institut für Umweltphysik/Fernerkundung Physik/ElektrotechnikFachbereich 1SCIAMACHY Instrument


130 - 160InGaAs0.262265 - 23808802 - 90545°130 - 160InGaAs0.221940 - 20407

2265 - 23806190 - 210InGaAs1.481000 - 175061508 - 16455225 - 235Si0.54785 - 10505

805 - 9004215 - 235Si0.48604 - 8054

617 - 7053215 - 235Si0.44394 - 6203450 - 5252185 - 215Si0.26309 - 4052310 - 3771185 - 215Si0.24240 - 3141

Spectral range[nm]

PMDOperatingtemperatureDetectormaterial

Spectralresolution

[nm]

Spectral range[nm]

channel

SCIAMACHY Detector and PMD characteristics

Each channel has 1024 diode elements on a 25 µm pitch.Channels 1 - 5 : ReticonChannels 6 - 7 : Epitaxx

Institut für Umweltphysik/Fernerkundung Physik/ElektrotechnikFachbereich 1Viewing Geometries

Institut für Umweltphysik/Fernerkundung Physik/ElektrotechnikFachbereich 1Limb/Nadir Matching

Institut für Umweltphysik/Fernerkundung Physik/ElektrotechnikFachbereich 1Typical Orbit

• Sun-synchronous orbit(10:00 AM)

• Limb twilightmeasurements beforesunrise

• Solar occultationmeasurement duringsunrise every orbit

• Alternating Nadir andLimb measurements ondayside

• Lunar occultationmeasurements possiblefor about one week/month

• Calibration measurementsduring Eclipse and indedicated orbits

• Global coverage in 6 days

Institut für Umweltphysik/Fernerkundung Physik/ElektrotechnikFachbereich 1SCIAMACHY Targets and Spectral Coverage

Institut für Umweltphysik/Fernerkundung Physik/ElektrotechnikFachbereich 1SCIAMACHY Measurements


Examples of Scientific Results (1/2)

Ozone depletion during SPE: Ratio of Ozone concentrations before (28. 10. 2003)and during (1. 11. 2003) the solar proton event in the northern (left) and southern (right)hemisphere (© G. Rohen, Chr. V. Savigny, ife):


Examples of Scientific Results (2/2)

LARGE SO2 plume over Middle East in June / July 2003:Fire in a sulphur plant in Qayyarah, Iraq

Institut für Umweltphysik/Fernerkundung Physik/ElektrotechnikFachbereich 1SCIAMACHY has been a very stable instrument

in its first two years of operation !

from DLR

2002

2003

2004

Sep. Oct. Nov. Dec.May June July Aug.

Jan. Feb. March April May June July Aug. Sep. Oct. Nov. Dec.

Jan. Feb. March April

Sep. Oct. Nov. Dec.May June July Aug.Jan. Feb. March April

NominalMeasurement

Decontamination (reduced measurement)

OCM or “ENVISAT off”

“SCIAMACHY off“


Lightpath through instrument components is described as product of Müllermatrices.

Assumption: Degradation of a component can be described as a scalar factor onthe corresponding Müller matrix.

M-factors are used in the 0-1b processor to compensate for the radiometricdegradation 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 time0, i.e. BOL.

Ideally, these reference spectra should be taken on-ground, but in practice this isnot possible because measurements of the unobscured sun cannot beperformed on-ground.

Therefore, „earliest“ in-flight measurements shall be taken as reference.

SCIAMACHY Monitoring Concept

Institut für Umweltphysik/Fernerkundung Physik/ElektrotechnikFachbereich 1SCIAMACHY Light Path Monitoring Results

• No fully calibrated Level 1 data available� No operational monitoring possible (especially: no m-factors)• Instead:

Analysis of Level 0 solar data using own calibration routines:– Average of data over state or scan phase– Dark current from Dark Current Model of (L1b verification) orbit 2509– Scan angle– Quantum efficiency (limited quality)– Sun-Earth distance

• Computed:– Ratios of spectra (similar to m-factors)– Time series of average signal per channel (trend analysis)– Reference time: 2 Aug 2002 (~ orbit 2200) (just after decontamination)


SCIAMACHY Light Path Monitoring Results: Channel 1



wrong timing of subsolarmeasurements

partial solareclipse

Large sunspots

ENVISAT Pointing

Institut für Umweltphysik/Fernerkundung Physik/ElektrotechnikFachbereich 1SCIAMACHY Light Path Monitoring Results: Channel 7

The Icing Problem

Rapiddecrease intransmissiondue to icingon detectors

Effect ofdecontamination, but …

?

Institut für Umweltphysik/Fernerkundung Physik/ElektrotechnikFachbereich 1SCIAMACHY Light Path Monitoring Results: Channel 8

The Icing Problem


Optical bench module (OBM) and scanner mechanism were calibrated extensively on-groundusing internal and external light sources.

First comparisons of radiances and irradiances measured by SCIAMACHY with independentsources indicate an error in the absolute radiometric calibration, which has a strong impact onthe quality of most level-1 data products.

An extensive analysis of the radiometric onground calibration measurements of SCIAMACHYhas been performed, and a new procedure has been developed to recalculate some of theradiometric key data from existing end-to-end measurements.

These calculations were primarily based on a subset of NASA sphere measurements (20"diameter internally illuminated sphere coated with BaSO4), performed in 1999/2000. The NASAsphere has a long history of providing accurate absolute radiances for NASA's SBUV2 andTOMS programs and has also been used for the validation of the GOME absolute radiancecalibration.

First tests with in-flight measurements show a significant improvement of the quality of the level-1 data products when using these new key data.

Radiometric Calibration (1/2)


Radiometric Calibration (2/2)

Institut für Umweltphysik/Fernerkundung Physik/ElektrotechnikFachbereich 1Summary and Conclusions

++ The SCIAMACHY instrument is operating successfully since the launch of ENVISAT inMarch 2002, a large number of scientific results have been produced.

- Currently, the operational long-term monitoring is still mainly limited by the non-availabilityof fully calibrated operational data products.

+ However, the monitoring results based on uncalibrated Level 0 data show that theSCIAMACHY instrument is generally in good shape.

+ Radiometric calibration is substantially enhanced by reanalysis of on-ground calibrationmeasurements

- There is some evidence for a slight degradation in the UV of about 3 % per year.+ This degradation is smaller than expected from experience with the precursor instrument

GOME.+ In the visible and near-infrared wavelength region SCIAMACHY is stable on a sub-percent

level.- The largest throughput variations occur in the IR channels due to detector icing. Throughput

reductions of up to 80 % are observed here .+ The sensitivity of the instrument can be fully recovered by a decontamination procedure,- but the ice layers keep coming back in an irregular fashion. A correction procedure for the

data processing is under development.

Institut für Umweltphysik/Fernerkundung Physik/ElektrotechnikFachbereich 1SCIAMACHY and more ....

www.sciamachy.de

instrument monitoring and calibration two years after...

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