Accounting for the effect of aerosols in GHGSat methane retrieval

Yu, Qiurun; Jervis, Dylan; Huang, Yi

GHGSat comprises a constellation of satellites with high spatial and spectral resolution that specialize in monitoring methane emissions at 1.65 inline-formulaµm. This study investigates the ability to accurately retrieve both the methane mixing-ratio enhancement (inline-formula M2inlinescrollmathml normal Δ X chem normal CH normal 4 32pt14ptsvg-formulamathimgfdde2d1935f5e081ead122dc5a8ad4f4 amt-17-3347-2024-ie00001.svg32pt14ptamt-17-3347-2024-ie00001.png ) and the aerosol optical depth (AOD) simultaneously from simulated GHGSat observations that incorporate angle-dependent scattering information. Results indicate that the sign of the inline-formula M3inlinescrollmathml normal Δ X chem normal CH normal 4 32pt14ptsvg-formulamathimg78b133a460e3031930515b5f0223a900 amt-17-3347-2024-ie00002.svg32pt14ptamt-17-3347-2024-ie00002.png bias when neglecting aerosols changes from negative to positive as surface albedo increases, which is consistent with previous studies. The bias in inline-formula M4inlinescrollmathml normal Δ X chem normal CH normal 4 32pt14ptsvg-formulamathimg7b863537dfd204aa94e1fa1238951cbf amt-17-3347-2024-ie00003.svg32pt14ptamt-17-3347-2024-ie00003.png is most pronounced when AOD is not simultaneously retrieved, ranging from inline-formula−3.0 % to 6.3 % with an AOD of 0.1, a 60° solar zenith angle, and a surface albedo of 0.2 for the nadir-only retrieval. Using multiple satellite viewing angles during the GHGSat observation sequence with a scattering angle ranging from 100 to 140°, the study shows that the mean bias and standard deviation of inline-formula M6inlinescrollmathml normal Δ X chem normal CH normal 4 32pt14ptsvg-formulamathimgc3dee0a0780a8e08802a32c80b0acfcf amt-17-3347-2024-ie00004.svg32pt14ptamt-17-3347-2024-ie00004.png are within 0.3 % and 2.8 % relative to the background. The correlation between simultaneously retrieved inline-formula M7inlinescrollmathml normal Δ X chem normal CH normal 4 32pt14ptsvg-formulamathimga28008053761495a4462ba5db4d64c4b amt-17-3347-2024-ie00005.svg32pt14ptamt-17-3347-2024-ie00005.png and AOD shifts from being positive to negative as surface albedo increases and the aerosol asymmetry factor decreases, signifying a transition of the dominant aerosol effect from aerosol-only scattering to aerosol–surface multiple scattering. The variety of scattering angle ranges has little impact on the performance of the multi-angle viewing method. This study improves the understanding of the impact of aerosols on the GHGSat inline-formula M8inlinescrollmathml normal Δ X chem normal CH normal 4 32pt14ptsvg-formulamathimg0b1cee303d255d47f7ff6679e01de468 amt-17-3347-2024-ie00006.svg32pt14ptamt-17-3347-2024-ie00006.png retrieval and provides guidance for improving future GHGSat-like point-source imagers.

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Yu, Qiurun / Jervis, Dylan / Huang, Yi: Accounting for the effect of aerosols in GHGSat methane retrieval. 2024. Copernicus Publications.

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