China News Service, Beijing, September 11 (Reporter Sun Zifa) The reporter learned from the Institute of Atmospheric Physics (Institute of Atmospheric Physics) of the Chinese Academy of Sciences (Institute of Atmospheric Physics) on September 11 that a new method and new system for carbon monitoring and accounting for China's next-generation carbon satellite (TanSat-2) proposed and developed by a team of Chinese scientists successfully achieved differentiated accounting of carbon sinks and man-made carbon emissions during simulation observations.
Schematic illustration of collaborative observations of carbon dioxide and solar-induced chlorophyll fluorescence from China's Next Generation Carbon Satellite to distinguish anthropogenic and ecological carbon budgets. Photo courtesy of the research team
This scientific research paper, which is described as putting a "magnifying glass" on carbon satellites and assisting the accurate accounting of the earth's carbon ledger, was jointly completed by the Institute of Atmospheric Research, Chinese Academy of Sciences, the Microsatellite Innovation Institute of the Chinese Academy of Sciences, and the University of Edinburgh in the United Kingdom. It was recently published in the professional academic journal "Progress in Atmospheric Science."
Carbon satellite's "magnifying glass" sees the carbon ledger clearly
Yang Dongxu, the first author of the paper and researcher at the Institute of Atmospheric Physics, Chinese Academy of Sciences, said that if the earth is imagined as a huge carbon ledger, human emissions are "expenses" and absorption by marine and terrestrial ecosystems is "income." This carbon balance occurs between the vast land, ocean and atmosphere. It is invisible and difficult to accurately calculate on a location-by-location and hour-by-hour basis. Satellite remote sensing provides new possibilities for solving it.
However, carbon satellites in the past have been able to observe the concentration of carbon dioxide in the atmospheric column from space and use atmospheric transport simulations to infer where this change comes from. However, just looking at changes in the concentration of carbon dioxide in the atmosphere is like seeing "changes in the account balance." It is not easy to distinguish whether the change comes from fossil fuel burning or from plant growth, respiration and ecosystem exchange. This is one of the core goals and tasks of China's next-generation carbon satellite: to allow the carbon ledger to not only be seen on a larger scale, but also to be broken down more clearly. It requires a "magnifying glass" to see clearly the details of the carbon ledger.
As a new satellite system designed to meet the needs of the next generation of global carbon monitoring, the design of China's next generation carbon satellite is based on the mechanism of the scientific carbon cycle of the Earth system. It is planned to be equipped with a hyperspectral grating spectrometer to observe greenhouse gases such as carbon dioxide and methane, and to conduct observations of solar-induced chlorophyll fluorescence. It has an instantaneous field of view of approximately 1,000 kilometers and a lateral sweep capability of 3,000 kilometers. It has a higher spatial and temporal sampling density, and has a greater opportunity to reduce observation gaps caused by clouds, aerosols, and low solar altitude angles.
Schematic diagram of 5-day observation coverage under a large wide scenario simulated by China's next-generation carbon satellite simulator. Photo courtesy of the research team
Yang Dongxu pointed out that this study puts two types of complementary clues into the same inversion framework: one is atmospheric carbon dioxide concentration, which reflects the comprehensive signal left in the air by surface carbon exchange; the other is sun-induced chlorophyll fluorescence, which is a weak "fluorescence signal" emitted by plants during photosynthesis, which can help identify the productivity of terrestrial ecosystems.
In layman's terms, carbon dioxide is like a "general ledger change" left in the atmosphere, while solar-induced chlorophyll fluorescence is more like a "live reminder" that plants are working. Combining the two types of observations can more effectively distinguish between natural carbon sinks and anthropogenic fossil fuel emissions.
“Virtual Earth” conducts simulation tests
Before China's next-generation carbon satellite actually goes into space, how do scientists evaluate how much improvement it can bring in the future? Yang Dongxu said that in order to test the satellite with high fidelity, the research team used the independently developed carbon satellite observation orbit simulator to comprehensively consider various influencing factors such as atmospheric conditions and surface characteristics to simulate the observation process and observation data of the satellite in space as realistically as possible.
Subsequently, the research team used the observation system simulation experiment to conduct a "mission rehearsal" for satellite observations: first, they set up a virtual carbon cycle world with known answers, then simulated the atmospheric column carbon dioxide concentration and solar-induced chlorophyll fluorescence data that China's next-generation carbon satellite may observe, and finally tested whether the inversion system can accurately "retrieve" preset carbon emissions and carbon sinks from these observations.
Simulation results show that under ideal low-bias conditions, the collaborative observations of carbon dioxide and solar-induced chlorophyll fluorescence from China's next-generation carbon satellite can significantly improve net primary productivity and fossil fuel combustion emission retrieval capabilities, and have obvious constraining potential for complex vegetation areas and anthropogenic emission areas.
The study also gave an important reminder that "large width is not a master key". When there are systematic deviations in observation data, more data may bring the deviations into the inversion system. Therefore, in the future, carbon satellites must not only "scan widely", but also "measure accurately."
The research team believes that global emission reduction and carbon neutrality goals require a credible monitoring, reporting and verification system, which is often referred to as measurable, monitorable, reportable and verifiable. If large-scale, wide-coverage, high-precision carbon dioxide, solar-induced chlorophyll fluorescence, and related auxiliary observations can be continuously obtained from space, scientists will be able to more independently assess carbon emission changes and ecosystem absorption capabilities in different regions.
Schematic diagram of the error of satellite observations in reducing carbon sources and sinks such as ecological and anthropogenic emissions. Photo courtesy of the research team
Yang Dongxu said that this research also provides a quantifiable evaluation framework for the design of China's next-generation carbon satellite and future carbon dioxide satellite missions - to find a more reasonable balance between width, accuracy, bias and inversion effect.
He emphasized that China's next-generation carbon satellite is an important "space pen" in the earth's carbon ledger, but satellites cannot complete all carbon monitoring tasks alone. Clouds, aerosols and pollution conditions will cause observation gaps, and complex surface surfaces will also introduce uncertainties. Therefore, reliable global and regional carbon flux monitoring requires the support of satellites, ground-based, aerial and in-situ observations.
