Pre-launch calibration results of the TROPOMI payload on-board the Sentinel-5 Precursor satellite

Kleipool, Quintus; Ludewig, Antje; Babić, Ljubiša; Bartstra, Rolf; Braak, Remco; Dierssen, Werner; Dewitte, Pieter-Jan; Kenter, Pepijn; Landzaat, Robin; Leloux, Jonatan; Loots, Erwin; Meijering, Peter; van der Plas, Emiel; Rozemeijer, Nico; Schepers, Dinand; Schiavini, Daniel; Smeets, Joost; Vacanti, Giuseppe; Vonk, Frank; Veefkind, Pepijn

doi:https://doi.org/10.5194/amt-11-6439-2018

Articles | Volume 11, issue 12

https://doi.org/10.5194/amt-11-6439-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Special issue:

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

https://doi.org/10.5194/amt-11-6439-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 11, issue 12

Research article

|

04 Dec 2018

Research article |

| 04 Dec 2018

Pre-launch calibration results of the TROPOMI payload on-board the Sentinel-5 Precursor satellite

Quintus Kleipool, Antje Ludewig, Ljubiša Babić, Rolf Bartstra, Remco Braak, Werner Dierssen, Pieter-Jan Dewitte, Pepijn Kenter, Robin Landzaat, Jonatan Leloux, Erwin Loots, Peter Meijering, Emiel van der Plas, Nico Rozemeijer, Dinand Schepers, Daniel Schiavini, Joost Smeets, Giuseppe Vacanti, Frank Vonk, and Pepijn Veefkind

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Final revised paper (published on 04 Dec 2018)
Preprint (discussion started on 13 Feb 2018)

Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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RC1: 'Referee report pdf file.', Anonymous Referee #1, 12 Mar 2018
- AC1: 'AR to referee #1', Quintus Kleipool, 02 May 2018
RC2: 'General & Technical comments on Ver.3', Anonymous Referee #2, 23 Mar 2018
- AC2: 'AR to referee #2', Quintus Kleipool, 02 May 2018

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

AR by Quintus Kleipool on behalf of the Authors (30 Aug 2018) Author's response Manuscript

ED: Referee Nomination & Report Request started (09 Sep 2018) by Jhoon Kim

RR by Anonymous Referee #1 (24 Sep 2018)

RR by Anonymous Referee #2 (01 Oct 2018)

Suggestions for revision or reasons for rejection

The reviewed Revision 5 is significantly improved over Revision 3. Sections are better organized and balanced, and more background information is provided to contextualize the presentation. While no further rewrite of the paper is needed, I have several comments that I would like addressed prior to publication.

The paper contains references to rows and columns throughout. While such terminology is appropriate when discussing detector effects, it is less so for issues such as radiometric response. Some figures, especially but not limited to Fig. 18, would be more informative if plotted versus wavelength.

The authors are still underplaying the importance of the BSDF calibration. The revised discussion makes clear there were pre-launch calibration problems that prevented a high-quality set of BSDF calibrations. But the instrument still has BSDF calibrations, as presented in Section 6.3. It is noteworthy that this section precedes sections dealing with relative radiance and irradiance, suggesting that these somehow do not affect the BSDF. There are three basic spectral frequency regimes of interest for the BSDF, listed with increasing importance to science products: wavelength-independent errors, broad wavelength dependence, and spectral structure. The authors present a relative BSDF uncertainty for each sensor channel, but do not say over what spectral frequency these values apply. The authors state the BSDFs are spectrally smooth, so the stated uncertainties clearly do not describe residual spectral structure. Fig. 18 suggests (it would benefit from improved quality) the BSDFs are not perfectly smooth, so the authors should provide an uncertainty component for the residual structure.

This section or the conclusions would benefit from some critical discussion of the results. By simply looking at Fig. 18 and with some knowledge of aluminum reflectance it is possible to see significant problems in the UV channel. Are the other channels better understood?

Section 6.6, entitled In-band straylight, contains a nice description of terminology but never tells us what in-band refers to. Is it all stray light that is not out-of-range? Or all stray light that is not out-of-band? The authors (in Section 6.7) seem to use these two terms interchangeably. In other words does in-band stray light ignore inter-band stray light, e.g. from VIS wavelengths into UV wavelengths?

Section 6.6 contains the statement, "The SLRF describes the relative straylight response of the system and is derived from on-ground calibration measurements." Which measurements were used and how were they used?

The discussion in Section 6.6 centers on the EWLS measurements, which evidently did not involve spectral cutoff filters. The omission of information about spectral stray light is glaring, regardless of how the requirements were defined. The numbers shown in Table 8 and in Fig. 25 are therefore rather misleading to the average reader. The authors state at the end of the section that laser PSFs form the basis for the processing correction, yet no quantitative assessment is provided. Even if the authors cannot estimate the effectiveness of the correction, they should report the total stray light correction at several wavelengths within each band.

Table 8 needs more explanation, either in the caption or in the text. What is the definition of stray light percent (what is the value in the denominator)? Same comment applies to Fig. 25.

Technical corrections:
Figure 17 appears to be mislabeled. Different lines should be columns instead of rows.
Section 6.6, paragraph 3. Tol et al. (2018) should be followed by a period or semi-colon.
Figure 23 caption. The fifth sentence is poorly formed.

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ED: Publish subject to minor revisions (review by editor) (20 Oct 2018) by Jhoon Kim

AR by Quintus Kleipool on behalf of the Authors (29 Oct 2018) Author's response Manuscript

ED: Publish as is (14 Nov 2018) by Jhoon Kim

AR by Quintus Kleipool on behalf of the Authors (21 Nov 2018)

Short summary

This paper reports on the pre-launch calibration of the TROPOMI instrument on board ESA's Sentinel 5P satellite. This calibration is needed to convert the raw instrument digital data to physical quantities like Earth radiance and Sun irradiance. From these quantities atmospheric properties can be derived. The paper shows that the chosen approach to calibration and analysis was successful and that the achieved accuracy makes high-quality observations of the Earth's atmosphere feasible.