General comments

Methane is second most important greenhouse gas in Earth's atmosphere, and a large possible source is melting permafrost. Timely detection of

increased CH4 emission from melting permafrost is therefore an interesting and relevant research question. The authors try to answer that question by performing an OSSE with three observing platforms and increased CH4 emissions from Yedoma soils in the Arctic. The changes in CH4 can be detected and attributed best when the platforms are used in combination or over longer time periods. Since the article adresses a relevant sicientific topic from an instrumentation perspective, it

should be published after consideration of the specific comments given below.

The paper uses outdated versions of the EDGAR emission database and TROPOMI retrieval products (see specific comments), without a proper justification. At the very least, such a justification should be added to the paper, but the paper would be more relevant if the OSSEs were based on recent datasets.

Specific comments

*) page 3, line 125: it is mentioned that the model as a 0.5 degree

   horizontal resolution. But the horizontal extent is not mentioned,

   is it global or regional? Figure 1 and 5 only show latitude >~ 50N.

*) page 3, line 128: Why use EDGAR v4.3.2 (which is apparently from

   2017, even though the cited publication is from 2019.

   See https://edgar.jrc.ec.europa.eu/archived_datasets) if more

   recent versions of the database are available (such as the 2024

   version EDGAR_2024_GHG)?

*) page 3, line 136: Why pick 2010 as baseline year? Later TROPOMI data

   from 2019 is used for the synthetic data. So you could have used

   actual TROPOMI data with measured cloud fractions etc..

   What would change if you modelled a longer time period?

*) page 3, line 137: do you only amplify the Yedoma gridcells and keep

   the emission from the non-Yedoma grid cells constant?

*) page 5, line 187: although the version numbering of TROPOMI SRON

   and operational retrievals could be improved, I think that v0017

   is an older version of the SRON retrieval product. Lorente et al.

   (2022, https://doi.org/10.5194/amt-2022-255) describe important

   updates to the algorithm improving the retrievals. These updates

   have since then been incorporated into the operational (reprocessed)

   product. The question is therefore, why use an older version of the

   product?

*) page 5, line 189: Why use version 1.5 of the WFMD product?

   Version 1.8 has been available for years

   (e.g. https://doi.org/10.5194/amt-16-669-2023)

   while the most recent version is 2.0:

   https://www.iup.uni-bremen.de/carbon_ghg/products/tropomi_wfmd/index.php

*) page 5, line 189/190: The sentence "Both of these products only

   contain successful retrievals." is incorrect. These products do contain

   e.g. non converged retrievals, but you can (and probably should) select

   only the successful retrievals with the provided quality flags.

*) page 5, line 199: "... fitting a curve to reported uncertainties..."

   Please provide a plot with this fit.

*) page 5~7, sections 2.3 and 2.4: How is the model sampled for satellite

   observations? Is the averaging kernel taken into account?

*) page 7, line 256-257: wrt. the t-test, is the test statistic used in

   a one or two-tailed significance test, and what about the null and

   alternative hypotheses?

*) page 11~13, figures 6~8: why use 28-day bin sizes while in lines

   277-279 (page 7) it is mentioned that "for the remaining evaluation

   we focus on the 112 day bin..."?

Technical corrections

*) page 1, line 3: affiliation of last author (Gockede) is missing.

*) page 1, line 15: please change satellites to satellite instruments.

*) page 2, line 85: since this is the first mention after the abstract

   of MERLIN, please provide the full instrument name in addition to

   the acronym.

*) page 6, table 1: fix the vertical alignent of the cell "Ice, TROPOMI"

   (containing the number 141461)

Please find the review in the attachment.