An 11-year record of XCO₂ estimates derived from GOSAT measurements using the NASA ACOS version 9 retrieval algorithm

Thomas E. Taylor , Christopher W. O'Dell , David Crisp , Akhiko Kuze , Hannakaisa Lindqvist , Paul O. Wennberg , Abhishek Chatterjee , Michael Gunson , Annmarie Eldering , Brendan Fisher , Matthäus Kiel , Robert R. Nelson , Aronne Merrelli , Greg Osterman , Frédéric Chevallier (1) , Paul I. Palmer , Liang Feng , Nicholas M. Deutscher , Manvendra K. Dubey , Dietrich G. Feist , Omaira E. García , David W. T. Griffith , Frank Hase , Laura T. Iraci , Rigel Kivi , Cheng Liu , Martine de Mazière , Isamu Morino , Justus Notholt , Young-Suk Oh , Hirofumi Ohyama , David F. Pollard , Markus Rettinger , Matthias Schneider , Coleen M. Roehl , Mahesh Kumar Sha , Kei Shiomi , Kimberly Strong , Ralf Sussmann , Yao Té (2) , Voltaire A. Velazco , Mihalis Vrekoussis , Thorsten Warneke , Debra Wunch

1 LSCE - Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette]
2 LERMA - Laboratoire d'Etude du Rayonnement et de la Matière en Astrophysique et Atmosphères = Laboratory for Studies of Radiation and Matter in Astrophysics and Atmospheres

The Thermal And Near infrared Sensor for carbon Observation - Fourier Transform Spectrometer (TANSO-FTS) on the Japanese Greenhouse gases Observing SATellite (GOSAT) has been returning data since April 2009. The version 9 (v9) Atmospheric Carbon Observations from Space (ACOS) Level 2 Full Physics (L2FP) retrieval algorithm (Kiel et al., 2019) was used to derive estimates of carbon dioxide (CO₂) dry air mole fraction (XCO₂) from the TANSO-FTS measurements collected over its first 11 years of operation. The bias correction and quality filtering of the L2FP XCO₂ product were evaluated using estimates derived from the Total Carbon Column Observing Network (TCCON) as well as values simulated from a suite of global atmospheric inversion systems (models) which do not assimilate satellite-derived CO₂. In addition, the v9 ACOS GOSAT XCO₂ results were compared with collocated XCO₂ estimates derived from NASA's Orbiting Carbon Observatory-2 (OCO-2), using the version 10 (v10) ACOS L2FP algorithm.

These tests indicate that the v9 ACOS GOSAT XCO₂ product has improved throughput, scatter, and bias, when compared to the earlier v7.3 ACOS GOSAT product, which extended through mid 2016. Of the 37 million soundings collected by GOSAT through June 2020, approximately 20 % were selected for processing by the v9 L2FP algorithm after screening for clouds and other artifacts. After post-processing, 5.4 % of the soundings (2×10⁶ out of 37×10⁶) were assigned a "good" XCO₂ quality flag, as compared to 3.9 % in v7.3 (<1 ×10⁶ out of 24×10⁶). After quality filtering and bias correction, the differences in XCO₂ between ACOS GOSAT v9 and both TCCON and models have a scatter (1σ) of approximately 1 ppm for ocean-glint observations and 1 to 1.5 ppm for land observations. Global mean biases against TCCON and models are less than approximately 0.2 ppm. Seasonal mean biases relative to the v10 OCO-2 XCO₂ product are of the order of 0.1 ppm for observations over land. However, for ocean-glint observations, seasonal mean biases relative to OCO-2 range from 0.2 to 0.6 ppm, with substantial variation in time and latitude.

The ACOS GOSAT v9 XCO₂ data are available on the NASA Goddard Earth Science Data and Information Services Center (GES-DISC) in both the per-orbit full format (https://doi.org/10.5067/OSGTIL9OV0PN, OCO-2 Science Team et al., 2019b) and in the per-day lite format (https://doi.org/10.5067/VWSABTO7ZII4, OCO-2 Science Team et al., 2019a). In addition, a new set of monthly super-lite files, containing only the most essential variables for each satellite observation, has been generated to provide entry level users with a light-weight satellite product for initial exploration (CaltechDATA, https://doi.org/10.22002/D1.2178, Eldering, 2021). The v9 ACOS Data User's Guide (DUG) describes best-use practices for the GOSAT data (O'Dell et al., 2020). The GOSAT v9 data set should be especially useful for studies of carbon cycle phenomena that span a full decade or more and may serve as a useful complement to the shorter OCO-2 v10 data set, which begins in September 2014.

Domaines: Planète et Univers [physics]

Thomas E. Taylor, Christopher W. O'Dell, David Crisp, Akhiko Kuze, Hannakaisa Lindqvist, et al.. An 11-year record of XCO₂ estimates derived from GOSAT measurements using the NASA ACOS version 9 retrieval algorithm. Earth System Science Data, 2022, 14, pp.325-360. ⟨10.5194/essd-14-325-2022⟩. ⟨insu-03717138⟩