A study of measurement scenarios for the future CO2M mission: avoidance of detector saturation and the impact on XCO<sub>2</sub> retrievals

Weimer, Michael; Hilker, Michael; Noël, Stefan; Reuter, Max; Buchwitz, Michael; Fuentes Andrade, Blanca; Lang, Rüdiger; Sierk, Bernd; Meijer, Yasjka; Bovensmann, Heinrich; Burrows, John P.; Bösch, Hartmut

doi:https://doi.org/10.5194/amt-18-3321-2025

Articles | Volume 18, issue 14

https://doi.org/10.5194/amt-18-3321-2025

© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/amt-18-3321-2025

© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 18, issue 14

Research article

|

21 Jul 2025

Research article |

| 21 Jul 2025

A study of measurement scenarios for the future CO2M mission: avoidance of detector saturation and the impact on XCO₂ retrievals

Michael Weimer, Michael Hilker, Stefan Noël, Max Reuter, Michael Buchwitz, Blanca Fuentes Andrade, Rüdiger Lang, Bernd Sierk, Yasjka Meijer, Heinrich Bovensmann, John P. Burrows, and Hartmut Bösch

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Final revised paper (published on 21 Jul 2025)
Preprint (discussion started on 22 Jan 2025)

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2024-3857', Anonymous Referee #1, 24 Feb 2025

See attached pdf for details. The question on the reason for the 308ms sampling time should be addressed before publication.

Citation: https://doi.org/10.5194/egusphere-2024-3857-RC1
- AC1: 'Reply on RC1', Michael Weimer, 14 Mar 2025
  
  Dear Referee,
  Thank you very much for your comprehensive review of our manuscript. Please find our responses in the attachment.
  
  Citation: https://doi.org/10.5194/egusphere-2024-3857-AC1
RC2:
'Comment on egusphere-2024-3857', Anonymous Referee #2, 26 Feb 2025

Please find the review comments on the preprint in the attached PDF file.

Citation: https://doi.org/10.5194/egusphere-2024-3857-RC2
- AC2: 'Reply on RC2', Michael Weimer, 14 Mar 2025
  
  Dear Referee,
  Thank you very much for your comprehensive review of our manuscript. Please find our responses in the attachment.
  
  Citation: https://doi.org/10.5194/egusphere-2024-3857-AC2

Peer review completion

AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload

AR by Michael Weimer on behalf of the Authors (14 Mar 2025) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (18 Mar 2025) by Piet Stammes

RR by Anonymous Referee #1 (31 Mar 2025)

Suggestions for revision or reasons for rejection

Dear authors,

Thank you for the detailed explanations in your answers. The additional analysis you have performed on discarding the entire swath if a part is saturated is very valuable. This gives a more realistic estimate of the remaining usable data. Do you also have a percentage for the data available after postprocessing for this case? It might be worthwhile adding this number if you have it readily available.
In your rework you have addressed many of my points in a satisfactory way. However, on the sampling interval/integration time discussion I still miss some fundamental information:
While acknowledging that there are constraints from mission requirements and hardware, it is also important for a scientific study to show very clearly what the fundamental limitations are in such a situation. This analysis is needed to make sure that the best choices and tradeoffs between the different requirements can be made for this mission. A possible non-compliance on the spatial sampling might be acceptable if the SNR and coverage could be improved significantly.
I do not fully follow the argumentation in your answer, of course the signal decreases if a shorter integration time is used, but when comparing the case for OSF=2, an exposure time of 234ms surely has a higher SNR than 2* 117ms? The total integration time is the same, but with two reads there will be twice the read-out noise and also a gap in the spatial sampling due to the read-out time.
So please add to your manuscript (without consideration for the prescribed values for the integration times) a table or curve with the integration time vs % of saturated pixels. What would be the optimal integration time for the CO2/NO2 instrument to avoid saturation? For SWIR 1 24.51% (value from Table 2) of the pixels are saturated for 271 ms, when would it be 10%, 5%, 1%? And what SNR would be expected then for NIR/SWIR1/SWIR2?

Kind regards,
Referee 1

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RR by Anonymous Referee #2 (12 Apr 2025)

ED: Publish subject to minor revisions (review by editor) (22 Apr 2025) by Piet Stammes

AR by Michael Weimer on behalf of the Authors (09 May 2025) Author's response Author's tracked changes Manuscript

ED: Publish as is (13 May 2025) by Piet Stammes

AR by Michael Weimer on behalf of the Authors (13 May 2025)

Short summary

Optical detectors have a maximum signal (saturation). Exceedance means that the measurement has to be discarded. We investigate where saturation will occur for the future European satellite mission dedicated to CO₂ monitoring (CO2M) and strategies to avoid saturation. Saturation impacts coverage and precision, both of which are important for estimation of local CO₂ emissions. We find that taking two pictures per sampling should be sufficient to avoid saturation for CO2M, with some impact on CO₂ precision.

A study of measurement scenarios for the future CO2M mission: avoidance of detector saturation and the impact on XCO2 retrievals

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Interactive discussion

Peer review completion

Suggestions for revision or reasons for rejection

A study of measurement scenarios for the future CO2M mission: avoidance of detector saturation and the impact on XCO₂ retrievals