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Volume 11, issue 7 | Copyright

Special issue: TROPOMI on Sentinel-5 Precursor: data products and...

Atmos. Meas. Tech., 11, 4493-4507, 2018
https://doi.org/10.5194/amt-11-4493-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 27 Jul 2018

Research article | 27 Jul 2018

Characterization and correction of stray light in TROPOMI-SWIR

Paul J. J. Tol1, Tim A. van Kempen1, Richard M. van Hees1, Matthijs Krijger1,2, Sidney Cadot1,3, Ralph Snel1,4, Stefan T. Persijn5, Ilse Aben1, and Ruud W. M. Hoogeveen1 Paul J. J. Tol et al.
  • 1SRON Netherlands Institute for Space Research, Utrecht, the Netherlands
  • 2Earth Space Solutions, Utrecht, the Netherlands
  • 3Jigsaw B.V., Delft, the Netherlands
  • 4Science and Technology B.V., Delft, the Netherlands
  • 5VSL Dutch Metrology Institute, Delft, the Netherlands

Abstract. The shortwave infrared (SWIR) spectrometer module of the Tropospheric Monitoring Instrument (TROPOMI), on board the ESA Copernicus Sentinel-5 Precursor satellite, is used to measure atmospheric CO and methane columns. For this purpose, calibrated radiance measurements are needed that are minimally contaminated by instrumental stray light. Therefore, a method has been developed and applied in an on-ground calibration campaign to characterize stray light in detail using a monochromatic quasi-point light source. The dynamic range of the signal was extended to more than 7 orders of magnitude by performing measurements with different exposure times, saturating detector pixels at the longer exposure times. Analysis of the stray light indicates about 4.4% of the detected light is correctable stray light. An algorithm was then devised and implemented in the operational data processor to correct in-flight SWIR observations in near-real time, based on Van Cittert deconvolution. The stray light is approximated by a far-field kernel independent of position and wavelength and an additional kernel representing the main reflection. Applying this correction significantly reduces the stray-light signal, for example in a simulated dark forest scene close to bright clouds by a factor of about 10. Simulations indicate that this reduces the stray-light error sufficiently for accurate gas-column retrievals. In addition, the instrument contains five SWIR diode lasers that enable long-term, in-flight monitoring of the stray-light distribution.

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The shortwave infrared (SWIR) spectrometer module of the Tropospheric Monitoring Instrument (TROPOMI) is used to measure atmospheric CO and methane columns from space. A method has been developed and applied in an on-ground calibration campaign to characterize stray light in detail. An algorithm was then devised to correct in-flight observations in near-real time, reducing the stray-light signal sufficiently for accurate gas-column retrievals.
The shortwave infrared (SWIR) spectrometer module of the Tropospheric Monitoring Instrument...
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