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- Title
甲烷柱浓度红外高光谱遥感反演与验证.
- Authors
周, 敏强; 倪, 启晨; 王, 佳欣; 蔡, 兆男; 南, 卫东; 王, 普才
- Abstract
Methane (CH4) is the second most important greenhouse gas in the Earth's atmosphere, after carbon dioxide (CO2). Understanding the change in CH4 concentration is a challenging task in atmospheric research given that it has various sources. Remote sensing has now become an effective technique to monitor CH4 concentrations globally. In this study, we presented an overview of CH4 column retrievals based on ground-based Fourier Transform Infrared spectrometer (FTIR) and space-based infrared measurements. Satellite validations were also discussed. Currently, three ground-based remote sensing international observation networks provide CH4 columns: the Total Carbon Column Observing Network (TCCON), the NDACC-IRWG (Network for the Detection of Atmospheric Composition Change - the Infrared Working Group), and the COCCON (COllaborative Carbon Column Observing Network). The main characteristics of the three networks were presented and discussed in our study, such as the measurement instrument, the observed spectra, the retrieval algorithm, and the post-correction. TCCON and COCCON provide dry-air column-averaged mole fraction of CH4 (XCH4) measurements, with a systematic/random uncertainty of 0.1/0.5%. NDACC provides a total column of CH4, with a slightly large systematic/random uncertainty of 0.2/1.0%. However, it also provides a vertical profile of CH4, which allows us to observe the CH4 variations in the troposphere and stratosphere separately. Regarding the satellite CH4 retrievals, we compared several popular sensors with a nadir-view geometry and their retrieval algorithms, such as the TANSO-FTS/GOSAT, TROPOMI/S5P, IASI/MetOp, and AIRS/Aqua. Basically, the short-wave infrared measurements (GOSAT and TROPOMI) have more sensitivity to the low troposphere, while the thermal infrared measurements (IASI and AIRS) are mainly sensitive to the mid- and upper troposphere. The difference in their vertical sensitivity comes from the CH4-specific absorption lines in the infrared region. All satellite retrievals are affected by the cloud, aerosol, and surface parameters. They also need to be validated and calibrated against ground-based measurements. Here, key steps during the satellite CH4 validation were discussed, including the statistical parameters, the a priori substitution, the smoothing correction, and the surface altitude correction. Finally, we showed the CH4 retrievals observed by the ground-based FTIR system at Xianghe, North China. We operated TCCON-type and NDACC-type measurements for the Bruker 125HR instrument and COCCON-type measurements for the Bruker EM27/SUN instrument. The entire FTIR measurement system at Xianghe was well described. Then, we used the TCCON X C H 4 measurements to validate the co-located TROPOMI satellite observations within 50 km at Xianghe. The mean difference between TCCON and TROPOMI X C H 4 measurements from June 2018 to May 2021 is 0.109% (nearly 2 ppb), which is within the retrieval uncertainty of the TROPOMI measurement. Moreover, a high correlation (R = 0.92) is found between TCCON and TROPOMI X C H 4 measurements at Xianghe. However, the annual growth of X C H 4 derived from the TROPOMI satellite measurements is 0.263% ± 0.172%/year larger than that derived from the TCCON measurements. Besides, seasonal variation is observed in the differences between TCCON and TROPOMI X C H 4 measurements, and the differences are obvious when the surface albedo is less than 0.1. Therefore, further investigations are needed to improve the TROPOMI CH4 retrievals in North China.
- Subjects
FOURIER transform spectrometers; ATMOSPHERIC composition; ATMOSPHERE; MOLE fraction; REMOTE sensing
- Publication
Journal of Remote Sensing, 2024, Vol 28, Issue 8, p1968
- ISSN
1007-4619
- Publication type
Article
- DOI
10.11834/jrs.20242530