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

    A simple and quick sensitivity analysis method for methane isotopologues detection with GOSAT-TANSO-FTSCrossref
    This article is timely and useful, even for the non-specialist, but it could be enhanced
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    A simple and quick sensitivity analysis method for methane isotopologues detection with GOSAT-TANSO-FTS

     Edward Malina (corresponding) ,  Jan-Peter Muller,  David Walton (2019)
    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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      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

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      Review text

      This is a welcome review of how satellite observations can be used to differentiate between methane from biogenic and industrial sources from the isotope signatures in infra-red absorption. The study is based mainly on the Japanese GOSAT data and it is a good introduction to students about Radiation Transfer Modelling, but with the proviso that the students are already very familiar with infra-red adsorption and light scattering physics.

      The paper would have much wider appeal if there were explanatory diagrams about the mechanisms of light scattering/adsorption in an introductory section. For example a simple diagram to explain what the GOSAT-TANSO-FTS actually measures would make a large difference to the understanding of the work and give this much more general appeal. The data permits detection  of 13CH4, and the ratio of 13 CH­­4 and 12 CH4 known as δ 13 C. This subject has a lot of acronyms, and an explanatory box listing these would also be very helpful.

      Generally the attention to detail about the modelling is clear, but a reader new to the subject would like to know more about the real utility of this approach. For example it would be useful to see if the methodology has been able to pick out geographical regions where the biogenic  methane dominates the industrial methane, so a spatial map of δ 13 C would be useful.

      Finally some comment about the methane released from methane clathrates should be included in the paper. These may assume increasing importance as the Arctic and Antarctic regions warm and release such methane.


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