Toward High Precision XCO2 Retrievals From TanSat Observations: Retrieval Improvement and Validation Against TCCON Measurements

D Yang; H Boesch; Y Liu; P Somkuti; Z Cai; X Chen; A Di Noia; C Lin; N Lu; D Lyu; R J Parker; L Tian; M Wang; A Webb; L Yao; Z Yin; Y Zheng; N M Deutscher; D W T Griffith; F Hase; R Kivi; I Morino; J Notholt; H Ohyama; D F Pollard; K Shiomi; R Sussmann; Y Té; V A Velazco; T Warneke; D Wunch

doi:10.1029/2020JD032794

Toward High Precision XCO₂ Retrievals From TanSat Observations: Retrieval Improvement and Validation Against TCCON Measurements

J Geophys Res Atmos. 2020 Nov 27;125(22):e2020JD032794. doi: 10.1029/2020JD032794. Epub 2020 Nov 9.

Authors

D Yang^{1

2

3}, H Boesch^{1

4}, Y Liu^{2

3}, P Somkuti^{1

4

5}, Z Cai², X Chen², A Di Noia^{1

4}, C Lin⁶, N Lu⁷, D Lyu², R J Parker^{1

4}, L Tian⁸, M Wang³, A Webb^{1

4}, L Yao², Z Yin⁸, Y Zheng⁶, N M Deutscher⁹, D W T Griffith⁹, F Hase¹⁰, R Kivi¹¹, I Morino¹², J Notholt¹³, H Ohyama¹², D F Pollard¹⁴, K Shiomi¹⁵, R Sussmann¹⁰, Y Té¹⁶, V A Velazco⁹, T Warneke¹³, D Wunch¹⁷

Affiliations

¹ Earth Observation Science, School of Physics and Astronomy University of Leicester UK.
² Institute of Atmospheric Physics Chinese Academy of Sciences China.
³ Shanghai Advanced Research Institute Chinese Academy of Sciences Shanghai China.
⁴ National Centre for Earth Observation University of Leicester UK.
⁵ Colorado State University Fort Collins CO USA.
⁶ Changchun Institute of Optics, Fine Mechanics and Physics China.
⁷ National Satellite Meteorological Center, China Meteorological Administration China.
⁸ Shanghai Engineering Center for Microsatellites China.
⁹ Centre for Atmospheric Chemistry, School of Earth, Atmospheric and Life Sciences University of Wollongong NSW Australia.
¹⁰ Karlsruhe Institute of Technology, IMK-IFU Garmisch-Partenkirchen Germany.
¹¹ Space and Earth Observation Centre Finnish Meteorological Institute Finland.
¹² National Institute for Environmental Studies (NIES) Tsukuba Ibaraki Japan.
¹³ Institute of Environmental Physics (IUP) University of Bremen Bremen Germany.
¹⁴ National Institute of Water and Atmospheric Research Ltd (NIWA) Lauder New Zealand.
¹⁵ Japan Aerospace Exploration Agency Japan.
¹⁶ Laboratoire d'Etudes du Rayonnement et de la Matière en Astrophysique et Atmosphères (LERMA-IPSL) Sorbonne Université, CNRS, Observatoire de Paris, PSL Université Paris France.
¹⁷ University of Toronto Canada.

Abstract

TanSat is the 1st Chinese carbon dioxide (CO₂) measurement satellite, launched in 2016. In this study, the University of Leicester Full Physics (UoL-FP) algorithm is implemented for TanSat nadir mode XCO₂ retrievals. We develop a spectrum correction method to reduce the retrieval errors by the online fitting of an 8^th order Fourier series. The spectrum-correction model and its a priori parameters are developed by analyzing the solar calibration measurement. This correction provides a significant improvement to the O₂ A band retrieval. Accordingly, we extend the previous TanSat single CO₂ weak band retrieval to a combined O₂ A and CO₂ weak band retrieval. A Genetic Algorithm (GA) has been applied to determine the threshold values of post-screening filters. In total, 18.3% of the retrieved data is identified as high quality compared to the original measurements. The same quality control parameters have been used in a footprint independent multiple linear regression bias correction due to the strong correlation with the XCO₂ retrieval error. Twenty sites of the Total Column Carbon Observing Network (TCCON) have been selected to validate our new approach for the TanSat XCO₂ retrieval. We show that our new approach produces a significant improvement on the XCO₂ retrieval accuracy and precision when compared to TCCON with an average bias and RMSE of -0.08 ppm and 1.47 ppm, respectively. The methods used in this study can help to improve the XCO₂ retrieval from TanSat and subsequently the Level-2 data production, and hence will be applied in the TanSat operational XCO₂ processing.

Keywords: CO2; TanSat; retrieval algorithm; satellite.