Spectral sizing of a coarse-spectral-resolution satellite sensor for XCO<sub>2</sub>

Wilzewski, Jonas Simon; Roiger, Anke; Strandgren, Johan; Landgraf, Jochen; Feist, Dietrich G.; Velazco, Voltaire A.; Deutscher, Nicholas M.; Morino, Isamu; Ohyama, Hirofumi; Té, Yao; Kivi, Rigel; Warneke, Thorsten; Notholt, Justus; Dubey, Manvendra; Sussmann, Ralf; Rettinger, Markus; Hase, Frank; Shiomi, Kei; Butz, André

doi:https://doi.org/10.5194/amt-13-731-2020

Articles | Volume 13, issue 2

https://doi.org/10.5194/amt-13-731-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/amt-13-731-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 13, issue 2

Research article

|

13 Feb 2020

Research article |

| 13 Feb 2020

Spectral sizing of a coarse-spectral-resolution satellite sensor for XCO₂

Jonas Simon Wilzewski, Anke Roiger, Johan Strandgren, Jochen Landgraf, Dietrich G. Feist, Voltaire A. Velazco, Nicholas M. Deutscher, Isamu Morino, Hirofumi Ohyama, Yao Té, Rigel Kivi, Thorsten Warneke, Justus Notholt, Manvendra Dubey, Ralf Sussmann, Markus Rettinger, Frank Hase, Kei Shiomi, and André Butz

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Final revised paper (published on 13 Feb 2020)
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Preprint (discussion started on 06 Aug 2019)

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Status: closed

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

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RC1: 'Review of study by Wilzewski et al.', Anonymous Referee #1, 03 Sep 2019
- AC1: 'Reply to Reviewer #1', Jonas Wilzewski, 01 Nov 2019
RC2: 'comments', Anonymous Referee #2, 03 Sep 2019
- AC2: 'Reply to Reviewer #2', Jonas Wilzewski, 01 Nov 2019
RC3: 'review of ATM-2019-227', Anonymous Referee #3, 16 Sep 2019
- AC3: 'Reply to Reviewer #3', Jonas Wilzewski, 01 Nov 2019

Peer-review completion

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

AR by Jonas S. Wilzewski on behalf of the Authors (01 Nov 2019) Author's response Manuscript

ED: Referee Nomination & Report Request started (10 Nov 2019) by Michel Van Roozendael

RR by Anonymous Referee #2 (16 Nov 2019)

RR by Anonymous Referee #4 (05 Jan 2020)

Suggestions for revision or reasons for rejection

Review of “Spectral Sizing of a Coarse Spectral Resolution Satellite Sensor for XCO2”

General comments:

The manuscript presents a study of a potential hypothetical coarse spectral resolution satellite sensor for measuring XCO2 with a ground resolution on the order of 50 x 50 m2. The sensor should be able to discriminate plumes from background concentration fields on the scale of hundreds of meters to a few kilometers. The authors made sensitivity tests with GOSAT cloud free measurements for two SWIR bands and drew conclusions based on the comparisons to the native GOSAT resolution and ground-based reference measurements from the TCCON.

In this study the GOSAT spectra were degraded to lower spectral resolution without further noise being added. As the authors stated, it is important to be aware that their results are only representative under circumstances where the noise can be assumed to be smaller compared to other sources of error. Due to spectral downgrading, the SNR of the coarse resolution spectra is higher as compared to the native GOSAT spectra. However, the effect of measuring at a coarser ILS will also influence the noise and result in lower SNR and this is relevant as the current study is done with significantly higher SNR. The precision calculation shown in this study is valid for the special case where the SNR is very high. Therefore, this has to be clearly mentioned in the conclusions section of the paper. E.g. on page 17 line 1: it would be useful to add – “without further addition of noise to the spectra” for the years 2009 to 2016.

Page 1 line 10: please also include the information that no further noise was added while degrading the spectra.

Page 2 line 2: Resolving power of SWIR-1 and SWIR-2 bands are interchanged here – typo?

Page 5 line 17: Please rephrase the sentence “Since we want …” highlighting the fact that you do not compensate the degradation of the spectral resolution with the addition of the corresponding noise to the spectra but rather keep the same level of noise as in the native high resolution spectra.

Page 10 line 6: Further information on large biases for some TCCON stations would be useful e.g. Sodankyla, Bremen, Lamont, Edwards

Page 12 line 7: mean difference (“bias”) of 0.59 ppm for SWIR-1 and -0.29 ppm for SWIR-2 -> note that the bias values for the SWIR-1 and SWIR-2 are mentioned differently in Fig 9 and 10 – please check or explain why they are different.

Specific comments:

Page 2 line 5: please switch TCCON-GOSAT by GOSAT-TCCON as the latter is the reference.

Page 2 line 21: please include the full form of SCIAMACHY

Page 4 line 11: an -> and

Page 18 line 6: “from the two SWIR-2 bands” – why not use the third SWIR-2 band as well?

In my opinion, the paper is well written and well structured. I therefore recommend publication after the above mentioned points have been addressed.

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ED: Publish subject to minor revisions (review by editor) (14 Jan 2020) by Michel Van Roozendael

AR by Jonas S. Wilzewski on behalf of the Authors (16 Jan 2020) Author's response Manuscript

ED: Publish as is (21 Jan 2020) by Michel Van Roozendael

AR by Jonas S. Wilzewski on behalf of the Authors (21 Jan 2020) Manuscript

Short summary

Through spectral degradation of GOSAT measurements in the 1.6 and 2.0 μm spectral bands, we mimic a single-band, passive satellite sensor for monitoring of CO₂ emissions at fine spatial scales. We compare retrievals of XCO₂ from these bands to TCCON and native GOSAT retrievals. At spectral resolutions near 1.3 nm, XCO₂ retrievals from both bands show promising performance, but the 2.0 μm band is favorable due to better noise performance and the potential to retrieve some aerosol information.

Spectral sizing of a coarse-spectral-resolution satellite sensor for XCO2

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Spectral sizing of a coarse-spectral-resolution satellite sensor for XCO₂