Global climate governance and greenhouse gas emission reduction are of great urgency. The volume fraction of atmospheric methane (CH₄) has been rising continuously since the industrial revolution and is now averaging about 1895.7×10^-9 globally. In addition, since the global warming potential of CH₄ is about 27-30 times higher than that of carbon dioxide (CO₂), the monitoring of atmospheric CH₄ becomes the focus and hotspot of carbon emission reduction.

Satellite remote sensing features fast detection speed, wide coverage, and rich information. It can conduct continuous and stable observations of atmospheric CH₄ with high temporal and spatial resolution and high precision on a global scale and can provide verification and support for the "bottom-up" emission inventory.

Relying on the rapid development of satellite detection technology and the urgency to reduce greenhouse gas emissions, a large number of satellites with CH₄ detection capabilities have emerged in the past two decades. The detection technology has become more mature with increasingly higher detection accuracy. Additionally, corresponding algorithms of various satellite sensors have also made a huge leap forward. Rapid advances in both sensors and algorithms enable us to better monitor the temporal and spatial variability of atmospheric CH₄ and its impact on climate change.

With the purpose to promote the further development of CH₄ satellite remote sensing and retrieval research and realize the dual carbon target, it is necessary to summarize and discuss the existing research progress and future development trends, which can provide scientific and technological support for China's low-carbon sustainable development.

Firstly, the development of atmospheric CH₄ satellites and sensors is reviewed and introduced. Early sensors mainly rely on the thermal infrared band of about 8 μm for CH₄ detection, and typical representatives include IMG, AIRS, and IASI (Table 1). Subsequently, a series of passive short-wave infrared sensors represented by SCIAMACHY, TANSO-FTS, and TROPOMI are developed. They rely on CH₄ characteristic bands near 1.6 μm and 2.3 μm for detection and are more sensitive to changes in near-surface CH₄ concentration. Among them, the high-resolution imaging spectral sensors and platforms represented by GHGSat, AHSI, and MethaneSAT also take advantage of their high spectral resolution and high spatial resolution to monitor the CH₄ point source emissions. There is no doubt that new energy is injected into the development of CH₄ satellite remote sensing (Table 2). In recent years, active detection represented by the methane remote sensing lidar mission (MERLIN) has also developed rapidly, effectively making up for the shortcomings of passive remote sensing detection with improved detection efficiency.

Subsequently, the principles, application conditions, and retrieval accuracy of different sensor algorithms are summarized. From the early DOAS algorithm, proxy algorithm, and PPDF algorithm, to the most commonly employed full-physical algorithm with the highest precision at this stage, the physical algorithms have been continuously improved with enhanced efficiency and accuracy. The full-physical algorithms represented by NIES-FP, UoL-FP, RemoTeC, RemoTAP, IAPCAS, and FOCAL have an accuracy of 6×10^-9. At the same time, with the rapid development of computer technology and artificial intelligence, various new algorithms, such as neural network algorithms, are also emerging, which can almost complete the real-time retrieval of CH₄. These methods have also brought breakthroughs to CH₄ retrieval.

In the future, CH₄ detection satellite sensors will continue to develop toward the goal of high temporal and spatial resolution, high precision, high accuracy, and continuous observation. Many high-performance satellites such as MethaneSAT, Sentinel-5, and CO2M are under planning (Fig. 5). Furthermore, the construction of the satellite network should be stepped up to meet the demands of CH₄ global high-precision detection. Correspondingly, new requirements are put forward for the accuracy, coverage, and calculation speed of CH₄ observation data and retrieval products. For the most accurate full-physical algorithm at present, the adoption of more accurate forward radiative transfer models and prior information, collaborative retrieval and correction of clouds and aerosols, and multi-satellite joint retrieval and verification are all important means for algorithm improvement.

With the accelerated global climate governance and reduced greenhouse gas emissions, more and more countries have formulated and implemented a series of CH₄ emission reduction measures, and China has also proposed the dual carbon target, which is steadily advancing. However, the issues of climate governance and carbon emissions are very complex, and to some extent have even become the focus of competition among countries. In this context, the development of China's atmospheric CH₄ satellite remote sensing cannot be slackened and should be highly valued and vigorously developed to seize opportunities. China has deployed the launch of the next-generation carbon satellite task, which will implement the main passive observation, and significantly broaden the range of detection time and space. Finally, the spatial and temporal resolution is improved to promote an effective amount of data and realize the full range of high-precision detection, thus providing a solid foundation and strong support for realizing a dual carbon target.