Abstract
Satellite observation is one of the main methods used to monitor the global distribution and variation of atmospheric carbon dioxide (CO2). Several CO2 monitoring satellites have been successfully launched, including Japan’s Greenhouse Gases Observing SATellite (GOSAT), the USA’s Orbiting Carbon Observatory-2 (OCO-2), and China’s Carbon Dioxide Observation Satellite Mission (TanSat). Satellite observation targeting the ground-based Fourier transform spectrometer (FTS) station is the most effective technique for validating satellite CO2 measurement precision. In this study, the coincident observations from TanSat and ground-based FTS were performed numerous times in Beijing under a clear sky. The column-averaged dry-air mole fraction of carbon dioxide (XCO2) obtained from TanSat was retrieved by the Department for Eco-Environmental Informatics (DEEI) of China’s State Key Laboratory of Resources and Environmental Information System based on a full physical model. The comparison and validation of the TanSat target mode observations revealed that the average of the XCO2 bias between TanSat retrievals and ground-based FTS measurements was 2.62 ppm, with a standard deviation (SD) of the mean difference of 1.41 ppm, which met the accuracy standard of 1% required by the mission tasks. With bias correction, the mean absolute error (MAE) improved to 1.11 ppm and the SD of the mean difference fell to 1.35 ppm. We compared simultaneous observations from GOSAT and OCO-2 Level 2 (L2) bias-corrected products within a ±1° latitude and longitude box centered at the ground-based FTS station in Beijing. The results indicated that measurements from GOSAT and OCO-2 were 1.8 ppm and 1.76 ppm higher than the FTS measurements on 20 June 2018, on which the daily observation bias of the TanSat XOC2 results was 1.87 ppm. These validation efforts have proven that TanSat can measure XCO2 effectively. In addition, the DEEI-retrieved XCO2 results agreed well with measurements from GOSAT, OCO-2, and the Beijing ground-based FTS.
Highlights
Carbon dioxide (CO2) is the dominant anthropogenic greenhouse gas in the atmosphere and plays an important role in global climate change [1]
As the first retrieval of the TanSat target mode observations by the Department for Eco-Environmental Informatics (DEEI), the XCO2 results were validated with measurements from the Beijing ground-based Fourier transform spectrometer (FTS) station
This study performed the first validation of XCO2 from the TanSat target mode observations retrieved by the DEEI algorithm using measurements from the Beijing FTS site
Summary
Carbon dioxide (CO2) is the dominant anthropogenic greenhouse gas in the atmosphere and plays an important role in global climate change [1]. Affected by human activities such as the burning of fossil fuels and changes in land use, CO2 concentration has risen sharply from 280 parts per million (ppm) in pre-industrial times to 410 ppm in 2018; the annual growth reached 3 ppm in 2015. Current knowledge regarding the temporal and spatial variability of CO2 is still limited by data uncertainty caused by observation conditions and model simulation capability [2,3]. These limitations generate large gaps in our understanding of natural and anthropogenic surface carbon sources and sinks. Large-scale observations of the column-averaged dry-air mole fraction of CO2 (XCO2) can be obtained by satellite remote sensing
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