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    Review of 'A simple and quick sensitivity analysis method for methane isotopologues detection with GOSAT-TANSO-FTS'

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    A simple and quick sensitivity analysis method for methane isotopologues detection with GOSAT-TANSO-FTSCrossref
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        Rated 4.5 of 5.
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        Rated 4 of 5.
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        Rated 5 of 5.
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        Rated 5 of 5.
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        Rated 4 of 5.
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    A simple and quick sensitivity analysis method for methane isotopologues detection with GOSAT-TANSO-FTS

    Measurements of methane isotopologues can differentiate between different source types, be they biogenic (e.g. marsh lands) or abiogenic (e.g. industry). Global measurements of these isotopologues would greatly benefit the current disconnect between top-down (knowledge from Chemistry Transport Models and satellite measurements) and bottom-up (in situ measurement inventories) methane measurements. However, current measurements of these isotopologues are limited to a small number of in situ studies and airborne studies. In this paper we investigate the potential for detecting the second most common isotopologue of methane ( 13 CH 4 ) from space using the Japanese Greenhouse Gases Observation Satellite (GOSAT) applying a quick and simple residual radiance analysis technique. The method allows for a rapid analysis of spectral regions, and can be used to teach University students or advanced school students about radiative transfer analysis. Using this method we find limited sensitivity to 13 CH 4 , with detections limited to total column methane enhancements of >6%, assuming a desert surface albedo of >0.3.
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      Review information

      10.14293/S2199-1006.1.SOR-EARTH.AAKSMZ.v1.RZNNHZ
      This work has been published open access under Creative Commons Attribution License CC BY 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Conditions, terms of use and publishing policy can be found at www.scienceopen.com.

      Education,Earth & Environmental sciences,Physics
      SWIR,Methane,Education,Outreach,Climate,GOSAT,Radiative transfer,Isotopologue

      Review text

      This paper introduces a quick method to detect the methane isotopologues using Radiative Transfer Models. As described by authors, this is just a first step and the retrieval algorithm needs further development. The authors have also investigated the spectral distribution of the methane, and the potential error sources such as from water vapor and SCIATRAN. Overall, it is a clear and well-organized structure. I would recommend accept after only a few minor corrections listed as follows.

      Page 1 Line 40  :
      “the feasibility” should be “the feasibility of”
      Page 2 Line  18:
      “ethane” should be “methane”
      Page 3 Line 19-21
      The abbreviation “GOSAT21-TANSO-FTS” has been defined at Page 1 Line 43-44. Only define the abbreviation at the first time when it is used in the text.
      Page  5 Line 16 :
      “has significant pedigree ” should be “has a significant pedigree”
      Page 9 Line 14:
      Remove the extra Kuze et al
      Page  11 Line  41:
      “which take three” should be “which takes three”
      Page  14 Line  33 :
      would to be?
       

      Comments

      Dear Dr Luo,

       

      Thank you for your review and comments, please find our responses below. We have kept your original comments and responded in line in underlined text. 

       

      This paper introduces a quick method to detect the methane isotopologues using Radiative Transfer Models. As described by authors, this is just a first step and the retrieval algorithm needs further development. The authors have also investigated the spectral distribution of the methane, and the potential error sources such as from water vapor and SCIATRAN. Overall, it is a clear and well-organized structure. I would recommend accept after only a few minor corrections listed as follows.

       

      Thank you for your general positive comments.

       

      Page 1 Line 40  :
      “the feasibility” should be “the feasibility of”

       

      Thank you, this has been changed.


      Page 2 Line  18:
      “ethane” should be “methane”

       

      Thank you, however we do mean ethane here. The paper by Aydin et al (2011) used global variations of ethane as a proxy for methane variations.


      Page 3 Line 19-21
      The abbreviation “GOSAT21-TANSO-FTS” has been defined at Page 1 Line 43-44. Only define the abbreviation at the first time when it is used in the text.

       

      Thank you, this has been changed.


      Page  5 Line 16 :
      “has significant pedigree ” should be “has a significant pedigree”

       

      Thank you, this has been changed.


      Page 9 Line 14:
      Remove the extra Kuze et al

       

      Thank you, this has been changed.


      Page  11 Line  41:
      “which take three” should be “which takes three”

       

      Thank you, this has been changed.

       


      Page  14 Line  33 :
      would to be?

       

      Thank you, this has been changed to is to.

       

      In addition at this point in the manuscript, we have removed the following section:

       

      “We believe that a study using TCCON data should be a study in its own right, and does not fit in the context of the demonstration of the quick and simple methods we use in this paper.

      ”.

       

      This has been changed to:

       

      This work has been shown in a separate study, indicating that even with the improved SNR of the TCCON instruments, there are still significant challenges with retrievals of methane isotopologues (Malina et al., 2020).

       

      With best regards,

       

      Ed Malina & co-authors

       

       

      2020-12-13 21:23 UTC
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