## 3 Data Source and Methods  
### Data Source  
The GF-5B satellite is the second satellite of the Gaofen-5 series and was launched on 7 September 2021. It has accumulated over 2 years' worth of global observational data to date. Equipped with the Advanced Hyperspectral Imager (AHSI), it can capture spectral information spanning from 400 to 2500 nm, with a spatial resolution of 30 m over  
Figure 1: Study framework. a 60 km swath, encompassing 330 spectral channels with spectral resolutions of 5 and 10 nm in the visible to near-infrared (VNIR) and shortwave infrared (SWIR) spectroscopy, respectively [23; 24]. Its relatively high signal-to-noise ratio (around 500 in the SWIR) presents notable advantages in detecting methane point source emissions [25]. The retrieval of the enhancement of a column-averaged dry-air mole fraction of CH\({}_{4}\) (\(\Delta\)XCH\({}_{4}\)) relies primarily on the strong CH\({}_{4}\) absorption features near 2300 nm, while the 2100 to 2450 nm spectral window of the GF5-02-AHSI demonstrates higher sensitivity to XCH\({}_{4}\) variations, thereby possessing enhanced capabilities for precise methane concentration inversion. The EnMAP payload, jointly developed by the German Aerospace Center (Deutsches Zentrum fur Luft- und Raumfahrt, DLR) and Kayser-Threde GmbH, was launched in April 2022. It features a 30 km swath (Field of View, FOV = 2.63\({}^{\circ}\)), 30 m spatial resolution, and includes 242 spectral bands, with a range from 420 to 2450 nm [26]. The visible to near-infrared (VNIR) bands cover the range of 420 to 1000 nm, while the shortwave infrared (SWIR) bands span from 900 to 2450 nm. Utilizing the absorption characteristics in the SWIR region, EnMAP is capable of retrieving atmospheric methane concentrations, enabling the monitoring of areas with high methane levels globally. Researchers have employed EnMAP data to identify significant methane emissions from oil and gas infrastructure [25]. Sentinel-2 is a European Earth observation mission designed to provide operational data products for environmental risk management, land cover classification, land change detection, and terrestrial mapping [27]. It comprises two satellites positioned 180\({}^{\circ}\) out of phase in the same sun-synchronous orbit, with an Equator-crossing time of 10:30 (local solar time) at the descending node. Sentinel-2A was launched in June 2015, and Sentinel-2B in March 2017. Each satellite carries a multi-band instrument that continuously sweeps the Earth's surface in 13 spectral bands from the visible to the shortwave infrared (SWIR) at a 10-60 m pixel resolution over a 290 km cross-track swath. The twin satellite configuration enables full global coverage every five days. We use the Sentinel-2 Level-1C top-of-atmosphere reflectance data of the SWIR-1 (~1560-1660 nm) and SWIR-2 (~2090-2290 nm) bands to retrieve methane column enhancements [28]. The Sentinel-2 data are openly available on the European Space Agency's Copernicus Open Access Hub and with fixed geographic coordinates in the UTM/WGS84 projection. We present retrievals for two locations observed between January 2020 and June 2024. The first location is a coal mine facility in Changzhi, Shanxi, China: the Sanyuan Nan Yao Coal Mine (36\({}^{\circ}\)14\({}^{\prime}\)53\({}^{\prime\prime}\) N, 112\({}^{\circ}\)59\({}^{\prime}\)18\({}^{\prime\prime}\) E). The second is a device EOG Shale Gas Well in Eddy County, New Mexico (104\({}^{\circ}\)56\({}^{\prime}\)34\({}^{\prime\prime}\) W, 32\({}^{\circ}\)40\({}^{\prime}\)18\({}^{\prime\prime}\) N). [PERSON] et al. [29] conducted a study on it using the GHGSat-D demonstration satellite instrument. Sentinel-2 acquired 271 cloud-free observations at the Changzhi facility in Shanxi over a 4-year period, and 293 cloud-free observations at the EOG Shale Gas Well in Eddy County over a 4-year period.