Evaluation of the GOSAT/GOSAT-2 XCO2 proxy XCH4 product by comparison with TCCON observations over China
- 1Aerospace Information Research Institute (Beijing, China)
Abstract
Methane (CH ₄ ) is the second most important well-mixed greenhouse gas after carbon dioxide (CO ₂ ) and its accurate monitoring supports China's “dual carbon” goals. Satellites enable global CH ₄ monitoring using various sensors and retrieval techniques. The XCO ₂ proxy method derives the column-averaged dry-air mole fraction of CH ₄ (XCH ₄ ) from the XCH4/XCO2 ratio and an independent XCO ₂ estimate, exploiting the overlapping absorption bands of CH ₄ and CO ₂ near 1.6 µm and assuming similar vertical distributions to reduce common retrieval errors. In this study, four XCO ₂ proxy methane products, GOSAT SRPR, OCPR, FOCAL Proxy, and GOSAT-2 SRPR, are evaluated using Total Carbon Column Observing Network (TCCON) ground-based observations at the Hefei and Xianghe sites in China. GOSAT products show lower bias and RMSE at Xianghe than at Hefei, while GOSAT-2 products are similar at both sites, with lower bias, RMSE, and standard deviation compared with the GOSAT products and approximately 51 % of retrievals meeting GCOS requirements. All products, except OCPR, overestimate XCH ₄ at Hefei and underestimate XCH ₄ at Xianghe, due to XCO ₂ model errors and spatial differences associated with regional and local methane emissions affecting both sites. Furthermore, the overestimation of the ratio implies that the fundamental assumption of the XCO ₂ proxy method is not fulfilled, primarily due to systematic positive biases in the satellite-retrieved XCH ₄ used in the proxy calculation. This study provides key error characteristics and spatial-seasonal biases in current satellite proxy methane products over China, supporting future retrieval optimization.
Versions
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BibTeX
@article{jiang2026evaluation,
title = {{Evaluation of the GOSAT/GOSAT-2 XCO2 proxy XCH4 product by comparison with TCCON observations over China}},
author = {Xinran Jiang and Gerrit de Leeuw and Cheng Fan and Jeon-Teo Dong and Andrew Gerald Barr and Wei Wang and Minqiang Zhou and Zhengqiang Li},
journal = {Atmospheric Chemistry and Physics},
year = {2026},
month = oct,
doi = {10.5194/acp-26-15223-2026},
url = {https://doi.org/10.5194/acp-26-15223-2026},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Evaluation of the GOSAT/GOSAT-2 XCO2 proxy XCH4 product by comparison with TCCON observations over China
AU - Xinran Jiang
AU - Gerrit de Leeuw
AU - Cheng Fan
AU - Jeon-Teo Dong
AU - Andrew Gerald Barr
AU - Wei Wang
AU - Minqiang Zhou
AU - Zhengqiang Li
PY - 2026
DA - 2026/10/29
JO - Atmospheric Chemistry and Physics
DO - 10.5194/acp-26-15223-2026
UR - https://doi.org/10.5194/acp-26-15223-2026
AB - Methane (CH ₄ ) is the second most important well-mixed greenhouse gas after carbon dioxide (CO ₂ ) and its accurate monitoring supports China's “dual carbon” goals. Satellites enable global CH ₄ monitoring using various sensors and retrieval techniques. The XCO ₂ proxy method derives the column-averaged dry-air mole fraction of CH ₄ (XCH ₄ ) from the XCH4/XCO2 ratio and an independent XCO ₂ estimate, exploiting the overlapping absorption bands of CH ₄ and CO ₂ near 1.6 µm and assuming similar vertical distributions to reduce common retrieval errors. In this study, four XCO ₂ proxy methane products, GOSAT SRPR, OCPR, FOCAL Proxy, and GOSAT-2 SRPR, are evaluated using Total Carbon Column Observing Network (TCCON) ground-based observations at the Hefei and Xianghe sites in China. GOSAT products show lower bias and RMSE at Xianghe than at Hefei, while GOSAT-2 products are similar at both sites, with lower bias, RMSE, and standard deviation compared with the GOSAT products and approximately 51 % of retrievals meeting GCOS requirements. All products, except OCPR, overestimate XCH ₄ at Hefei and underestimate XCH ₄ at Xianghe, due to XCO ₂ model errors and spatial differences associated with regional and local methane emissions affecting both sites. Furthermore, the overestimation of the ratio implies that the fundamental assumption of the XCO ₂ proxy method is not fulfilled, primarily due to systematic positive biases in the satellite-retrieved XCH ₄ used in the proxy calculation. This study provides key error characteristics and spatial-seasonal biases in current satellite proxy methane products over China, supporting future retrieval optimization.
SN - 1680-7324
ER -