Characterization and correction of stray light in TROPOMI-SWIR

Paul J. J. Tol, Tim A. van Kempen, Richard M. van Hees, Matthijs Krijger, Sidney Cadot, Ralph Snel, Stefan T. Persijn, Ilse Aben, Ruud W. M. Hoogeveen

Research output: Contribution to JournalArticleAcademicpeer-review

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.
Original languageEnglish
Pages (from-to)4493-4507
Number of pages15
JournalAtmospheric Measurement Techniques
Volume11
Issue number7
DOIs
Publication statusPublished - 27 Jul 2018

Funding

Acknowledgements. The authors would like to thank the teams of Airbus Defence and Space Netherlands and KNMI for organizing the calibration campaign and the operators in particular for the tireless data acquisition. TROPOMI is a collaboration between Airbus Defence and Space Netherlands, KNMI, SRON and TNO, on behalf of NSO and ESA. Airbus Defence and Space Netherlands is the main contractor for the design, building and testing of the instrument. KNMI and SRON are the principal investigator institutes for the instrument. TROPOMI is funded by the following ministries of the Dutch government: the Ministry of Economic Affairs; the Ministry of Education, Culture and Science; and the Ministry of Infrastructure and the Environment. The authors would like to thank the teams of Airbus Defence and Space Netherlands and KNMI for organizing the calibration campaign and the operators in particular for the tireless data acquisition. TROPOMI is a collaboration between Airbus Defence and Space Netherlands, KNMI, SRON and TNO, on behalf of NSO and ESA. Airbus Defence and Space Netherlands is the main contractor for the design, building and testing of the instrument. KNMI and SRON are the principal investigator institutes for the instrument. TROPOMI is funded by the following ministries of the Dutch government: the Ministry of Economic Affairs; the Ministry of Education, Culture and Science; and the Ministry of Infrastructure and the Environment.

FundersFunder number
Ministerie van Economische Zaken
Ministerie van Onderwijs, Cultuur en Wetenschap
Ministry of Economic Affairs
Ministerie van Infrastructuur en Milieu

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