大气甲烷卫星传感器和遥感算法研究综述

Satellite Sensors and Retrieval Algorithms of Atmospheric Methane

全球气候治理和温室气体减排已经到了刻不容缓的地步。自工业革命以来,大气甲烷(CH_(4))体积分数一直持续上升,目前全球平均值已达约1895.7×10^(-9),加上CH_(4)全球变暖潜能值比二氧化碳(CO_(2))高约27~30倍,因此对大气CH_(4)的监测成为碳减排的重点与热点。利用卫星遥感探测速度快、覆盖范围广、获取信息丰富等优势,可以实现高精度、高时空分辨率且全球覆盖的大气CH_(4)浓度监测。据此,首先对大气CH_(4)探测卫星及传感器的发展进行梳理与介绍,从早期的被动热红外探测,到对近地CH_(4)浓度变化更为敏感的被动短波红外探测,再到以甲烷遥感激光雷达任务(MERLIN)为代表的主动型探测,CH_(4)探测传感器空间分辨率提升至5~10km,探测精度提升至10×10^(-9)以内,并朝着高时空分辨率、高精度和连续观测一体化的目标不断发展;然后,对各类传感器不同算法的原理、适用条件和反演精度等进行归纳总结,其中精度最高、应用最为广泛的全物理算法的反演精度已达到了0.3%;最后,结合大气CH_(4)卫星遥感发展现状与双碳目标的战略需求,对CH_(4)卫星遥感和反演研究的发展趋势进行总结与分析,旨在为我国大气CH_(4)卫星遥感体系建设提供一定的参考。

Significance Global climate governance and greenhouse gas emission reduction are of great urgency.The volume fraction of atmospheric methane(CH_(4))has been rising continuously since the industrial revolution and is now averaging about 1895.7× 10^(-9)lobally.In addition,since the global warming potential of CH,is about 27-30 times higher than that of carbon dioxide(CO_(2)),the monitoring of atmospheric CH,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 CH_(4) 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 CH_(4) 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 CH_(4) and its impact on climate change.With the purpose to promote the further development of CH,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.ProgressFirstly,the development of atmospheric CH_(4) satellites and sensors is reviewed and introduced.Early sensors mainly rely on the thermal infrared band of about 8μm for CH_(4)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 CH,characteristic bands near 1.6μm and 2.3μm for detection and are more sensitive to changes in near-surface CH_(4) 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 CH_(4) point source emissions.There is no doubt that new energy is injected into the development of CH_(4) 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 CH_(4).These methods have also brought breakthroughs to CH,retrieval.Conclusions and Prospects In the future,CH_(4) 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 CH_(4) global high-precision detection.Correspondingly,new requirements are put forward for the accuracy,coverage,and calculation speed of CH_(4) 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 CH_(4) 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 CH_(4) 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 highprecision detection,thus providing a solid foundation and strong support for realizing a dual carbon target.