Methane monitoring satellites – a new hotspot in greenhouse gas monitoring

The working principle of methane monitoring satellites is to estimate the total amount of methane by analyzing the spectral absorption of methane at different wavelengths. The remote sensing monitoring range covers the amount of methane in a columnar space from the satellite to the ground, and its main purpose is to obtain accurate, spatiotemporally continuous near-surface atmospheric CH4 concentration data.

Early spaceborne CH4 detection mainly used the thermal infrared band. However, since the emission radiation of the surface and near-surface atmosphere in the thermal infrared band is similar, it is difficult to distinguish between the two from the spectrum. As a result, the thermal infrared band is not sensitive to changes in CH4 concentration in the near-surface atmosphere and cannot meet the detection requirements of near-surface emission processes under the CH4 emission reduction target.

In comparison, the shortwave infrared spectrum contains CH4 absorption signals and surface reflection signals with significant differences in characteristics. According to the sensitivity comparison analysis of CH4 column concentration relative to CH4 profile, the shortwave infrared band is very sensitive to changes in near-surface atmospheric CH4 and is more suitable for monitoring CH4 emission processes.

Current status of methane monitoring satellite launch

△Summary of the performance of the CH4 satellites that have completed or are still in orbit

In recent years, with the rapid development of shortwave infrared CH4 spaceborne detection technology, multiple shortwave infrared detection satellites have been launched both domestically and internationally, carrying out a series of CH4 detection and related application studies. This has effectively promoted the development of CH4 satellite remote sensing inversion algorithms and flux inversion algorithms, laying a technical foundation for improving space exploration capabilities, producing data products, and directly applying them. Furthermore, it has demonstrated the application potential of shortwave infrared detection in global CH4 source-sink balance estimation from the perspectives of detection data accuracy and flux estimation.

methane monitoring satellite data acquisition

△Current status and planning of greenhouse gas monitoring satellites at home and abroad: Green indicates methane monitoring

The acquisition of accurate satellite-borne CH4 detection data requires the support of high-precision CH4 satellite remote sensing inversion algorithms. The quality of satellite-detected CH4 data products usually depends on the selection of detection instruments and inversion parameters.

Shortwave infrared (SIR) detection has the advantage of being sensitive to near-surface CH4 concentration changes, but its absorption spectrum is easily affected by atmospheric and surface parameters such as interfering gases, temperature, clouds, and aerosols, introducing significant errors. The goal of high-precision inversion algorithms is to reduce the influence of these interfering factors and extract the concentration information of the target gas from the effective spectral information. Internationally, various satellite remote sensing inversion methods for greenhouse gases have been established using the SCIAMACHY and GOSAT satellites. Among these, the most widely used are the all-physical model inversion algorithm, the proxy inversion method, and the WFM-DOAS inversion method.

All-physics inversion algorithms utilize forward models to simulate the atmospheric radiative transfer process of signals, significantly reducing errors caused by optical path uncertainties due to scattering during radiative transfer, and typically exhibit high inversion accuracy. Proxy algorithms usually use stable atmospheric components such as CO2 as representatives to correct the influence of clouds and aerosols on the optical path in the CH4 detection band, thereby extracting effective CH4 concentration information. The WFM-DOAS algorithm, based on classic differential absorption spectroscopy, uses a weighting function of the total amount of the target gas column to replace the absorption cross-section in the fitting of the differential absorption spectrum.

Methane monitoring future development trends

△Methane emissions from various sources in China in different months

Based on the existing technical means of CH4 detection satellite missions, in order to meet the detection and research needs at different scales, it is necessary to construct a constellation system to carry out collaborative detection using a combination of active and passive methods, and high and low orbit approaches. Future high spatiotemporal resolution global CH4 detection will primarily be achieved through satellite networking. By comprehensively applying the detection results from multiple satellites, scientific support will be provided for evaluating the effectiveness of carbon neutrality-related emission reduction measures and for global carbon inventory plans.

Xi'an Institute of Optics and Precision Mechanics CAS Aerospace Science and Technology Group Co.,LTD：First to deploy a commercial dual-carbon monitoring remote sensing satellite constellation

Based on the existing background, after extensive market research and user tracking, CAS Xiguang Aerospace has taken the lead in China by launching a commercial dual-carbon monitoring remote sensing satellite constellation plan based on ultra-fine spectral detection technology. They have designed China's first commercial methane monitoring satellite—XIGUANG-004—capable of monitoring the concentrations of major greenhouse gases. This satellite is a remote sensing satellite for monitoring carbon sources and sinks, equipped with a methane concentration detector, a chlorophyll fluorescence detector, and a multispectral imaging camera. It features multiple operating modes to meet the diverse needs of users targeting dual-carbon monitoring via satellite remote sensing.

The methane concentration detector achieves a spectral resolution of 0.1 nm and features quantitative detection of methane column concentration and quantification of methane column concentration above a target location. The chlorophyll fluorescence detector boasts a spectral resolution of up to 0.5 nm, effectively detecting subtle changes in the fluorescence spectrum produced during plant chlorophyll photosynthesis. This enables the assessment of total plant productivity and provides guidance for carbon trading. The multispectral imaging camera operates in eight visible light bands with a ground resolution of 10 m. It features a large aperture and low weight, primarily used for acquiring spectral and spatial images of ground features.

The satellite weighs 60 kg and can play a positive role in dual-carbon remote sensing monitoring and assessing the carbon neutrality potential of natural vegetation and artificial features. It will enable high-frequency, high-quantity, and high-coverage observation of global carbon emissions and carbon sinks, and take the lead in the development of commercial carbon satellites in China.

△Global methane emissions by sector, 1970-2018

In the face of the urgent situation of global climate change, reducing CH4 emissions is a necessary means to control global warming and achieve carbon neutrality. Satellite remote sensing can provide high spatiotemporal resolution global CH4 concentration data, greatly enhancing the data support capabilities for CH4 spatiotemporal dynamic monitoring, CH4 budget accounting, and emission reduction measure assessment, and providing a reference for addressing future climate change.

Some content in this article is sourced from:

Atmospheric Sciences IAP

Analysis of the Current Status and Development Trends of Atmospheric Methane Observation Satellites Aiming at Carbon Neutrality and Carbon Peak in my country

Yao Lu, Yang Dongxu, Cai Zhaonan, Zhu Sihong, Liu Yi, Deng Jianbo, Tian Longfei, Yin Zengshan, Lu Naimeng

Space Return and Remote Sensing, Voice of the Chinese Academy of Sciences

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