the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 27 Aug 2026
A consistent climate data record of atmospheric methane from the GOSAT and GOSAT-2 missions
Abstract. Understanding the renewed and accelerating growth of atmospheric methane requires satellite records that are long enough to span decadal change and consistent enough that instrumental differences are not mistaken for atmospheric signals. We present version 2.0 of the University of Leicester Proxy retrieval of column-averaged dry-air methane (XCH4) from the GOSAT-2 TANSO-FTS-2 instrument, comprising approximately 4.4 million quality-filtered soundings in land nadir and ocean glint observation modes between 5 February 2019 and 31 December 2025. The data are processed with the same algorithm, a priori fields, and quality-filtering framework as the established GOSAT Proxy v10.0 product, with the aim of producing a consistent multi-instrument climate data record. The on-board intelligent pointing of GOSAT-2 improves the yield of usable land soundings, particularly at coastal and island sites. The GOSAT-2 bias correction is cross-anchored to GOSAT over 124,206 matched-pair footprints and depends linearly on solar zenith angle. Anchoring to GOSAT rather than directly to the Total Carbon Column Observing Network (TCCON) leaves the corrected GOSAT-2 with a residual mean TCCON bias of +5.52 ppb, in exchange for sub-ppb inter-instrument consistency over the overlap period. Validation against the TCCON GGG2020.1 release yields a standard deviation of the satellite-minus-TCCON differences of 16.41 ppb and a correlation coefficient of 0.910 across 135,110 co-locations at 24 sites, compared to 16.42 ppb and 0.950 for GOSAT over 25 sites, demonstrating that GOSAT-2 reaches the precision of the heritage instrument. Co-located monthly 2° grid-cell means from GOSAT and GOSAT-2 during the 2019–2025 overlap correlate at 0.95 (land) and 0.97 (glint), with mean biases of +1.9 and +3.0 ppb. Beyond the cross-anchored correction, no further adjustment for either observation mode is required to merge the two records. The combined record forms a continuous Proxy XCH4 time series spanning 2009 to 2025, which will be extended as both missions continue to operate, and provides a reference for inter-comparison with TROPOMI and the next generation of greenhouse-gas monitoring missions. The GOSAT-2 Proxy XCH4 v2.0 dataset is available from the Centre for Environmental Data Analysis at https://doi.org/10.5285/8209b9acb92e4ba69188c9c8ff7a3b76 (Parker et al., 2026a).
- Preprint
(24451 KB) - Metadata XML
- BibTeX
- EndNote
Status: open (until 16 Oct 2026)
- RC1: 'Comment on essd-2026-625', Anonymous Referee #1, 13 Sep 2026 reply
Data sets
University of Leicester GOSAT-2 Proxy XCH4, v2.0 Robert J. Parker, Lakshmi N. Bharathan, Dan Orr, and Michael P. Cartwright https://catalogue.ceda.ac.uk/uuid/8209b9acb92e4ba69188c9c8ff7a3b76
University of Leicester GOSAT Proxy XCH4 v10.0 Robert J. Parker, Michael P. Cartwright, and Dan Orr https://catalogue.ceda.ac.uk/uuid/94d6572a308e477c86e0ce7c4d771311
Viewed
| HTML | XML | Total | BibTeX | EndNote | |
|---|---|---|---|---|---|
| 183 | 83 | 19 | 285 | 24 | 18 |
- HTML: 183
- PDF: 83
- XML: 19
- Total: 285
- BibTeX: 24
- EndNote: 18
Viewed (geographical distribution)
| Country | # | Views | % |
|---|
| Total: | 0 |
| HTML: | 0 |
| PDF: | 0 |
| XML: | 0 |
- 1
General Comments
The paper demonstrates that the GOSAT and GOSAT-2 can provide seamless dataset for almost 17 years with the world’s highest spectral resolution in orbit by using FTS technology. TANSO-FTS onboard GOSAT and TANSO-FTS-2 onboard GOSAT-2 have approximately the same spectral resolution, optical throughput, and interferogram acquisition time. However, their detector optics, electronics, and in-orbit thermal environments are different. These differences may affect the CH4 retrieval, which requires extremely high accuracy and precision to achieve decade-long monitoring. Additional description of differences such as polarization sensitivity and SZA-dependent bias would help readers better understanding. Overall, the paper is worth publication after minor revision.
Specific Comments
(1) Page 6, Line 133 “Optimized”
Spectral widths of Bands 1 and 3 of GOSAT-2 become wider than those of GOSAT. It is not clear why these widths are optimized. The authors should provide an explanation from the perspectives of information content and electrical noise etc.
(2) Page 7 Line 143 “gain settings”
Does GOSAT-2 use all 14 gain settings (3-16) in orbit, whereas GOSAT uses only 2 gain settings, high and medium? Is there any evidence that the finer gain setting of GOSAT-2 improve accuracy or precision of XCH4 retrievals?
(3) Page 7, Line 158 “wider”
What do the authors mean by “wider”? The GOSAT-2 revisit cycle is twice as long as that of GOSAT; however, the cross-track scanning angles of their pointing systems are similar.
(4) Page 9, Line 225 “intelligent pointing system”
The authors should mention that intelligent pointing is not applied to calibration and validation sites or to coastal region. For GOSAT-2, observations calibration and validation sites, such as TCCON sites, need to target the exact locations of these sites. The intelligent pointing algorithm may instead select area such as water surfaces or regions with complex topography, where retrieval quality can be degraded.
(5) Page 17, Line 390 “polarization”
The polarization sensitivity of GOSAT-2 is more complicated than that of GOSAT. The input scenes fluxes, including light scattered by aerosols, are also polarized. Polarization conditions differ between forward-viewing geometry (looking west toward the sun) and backward-viewing geometry (with the sun behind the satellite). Have the authors identified coincident observations from GOSAT and GOSAT-2 orbits under opposite viewing geometries and compared the retrieved results?
(6) Pages 19 and 20, Figures 7 and 8 “SZA dependent bias”
Fig 7 and Fig. 8 show that, before the bias correction, GOSAT-2 exhibits a larger SZA- dependent bias. These results suggest the difference may be related to the differences in instrument design and the in-orbit thermal environment. Is there any evidence that GOSAT-2 is more sensitive to temperature variations, such as those associated with the orbital phase?
Technical Correctiions
(1) Page 15, Line 352, “At the coastal sites (Tsukuba, Harwell) GOSAT-2 returns substantially more quality-filtered land soundings within the coincidence window than the regularly gridded GOSAT (Sect. 4.3), reflecting the improved GOSAT-2 acquisition strategy.”
Most GOSAT observations have been acquired in grid mode. However, Tsukuba is an important validation site and GOSAT has been targeting exact TCCON location using target mode. Please confirm.