Evaluating the consistency between OCO-2 and OCO-3 XCO₂ estimates derived from the NASA ACOS version 10 retrieval algorithm

Abstract

Abstract. The version 10 (v10) Atmospheric Carbon Observations from Space (ACOS) Level 2 Full Physics (L2FP) retrieval algorithm has been applied to multi-year records of observations from NASA's Orbiting Carbon Observatory -2 and -3 sensors (OCO-2 and OCO-3, respectively) to provide estimates of the carbon dioxide (CO2) column-averaged dry-air mole fraction (XCO2). In this study, a number of improvements to the ACOS v10 L2FP algorithm are described. The post-processing quality filtering and bias correction of the XCO2 estimates against multiple truth proxies are also discussed. The OCO v10 data volumes and XCO2 estimates from the two sensors for the time period August 2019 through February 2022 are compared, highlighting differences in spatiotemporal sampling, but demonstrating broad agreement between the two sensors where they overlap in time and space. A number of evaluation sources applied to both sensors suggest they are broadly similar in data and error characteristics. Mean OCO-3 differences relative to collocated OCO-2 data are approximately 0.2 ppm and −0.3 ppm for land and ocean observations, respectively. Comparison of XCO2 estimates to collocated Total Carbon Column Observing Network (TCCON) measurements show root mean squared errors (RMSE) of approximately 0.8 ppm and 0.9 ppm for OCO-2 and OCO-3, respectively. An evaluation against XCO2 fields derived from atmospheric inversion systems that assimilated only near-surface CO2 observations, i.e., did not assimilate satellite CO2 measurements, yielded RMSEs of 1.0 ppm and 1.1 ppm for OCO-2 and OCO-3, respectively. Evaluation of errors in small areas, as well as biases across land-ocean crossings, also show encouraging results, for each sensor and in their agreement. Taken together, our results demonstrate a broad consistency of OCO-2 and OCO-3 XCO2 measurements, suggesting they may be used together for scientific analyses.

Neutral Tropical African CO2 Exchange Estimated From Aircraft and Satellite Observations

“…This is illustrated in Figure S1 in Supporting Information S1 and in Figure 4 of Taylor et al. (2023). Fires play an important role in the African carbon cycle, but are thought to be compensated by CO 2 uptake during the growing season (Valentini et al., 2014).…”

Seasonal and Diurnal Variations in XCO2 Characteristics in China as Observed by OCO‐2/3 Satellites: Effects of Land Cover and Local Meteorology

“…Concise retrieval steps are discussed in Taylor et al. (2023). The SIF retrieval of both OCO‐2 and OCO‐3 is produced based on spectral fits covering Fraunhofer lines at 757 and 770.1 nm (Frankenberg et al., 2014; Sun et al., 2018) surrounding the O 2 A‐band.…”

“…Compared with the satellite remote sensing that receives solar radiation reflected back to space from the ground, direct light detection reduces the influence of factors such as clouds, aerosols, and surface albedo. Thus, TCCON plays an important role in providing an essential validation resource for the OCO‐2/3 satellites (Taylor et al., 2023; Wunch et al., 2017; Zhou et al., 2022a) and other spaceborne instruments such as GOSAT, GOSAT‐2, TanSat, and the Sentinel 5P instrument TROPOMI (Lorente et al., 2021; Noël et al., 2022; Yang et al., 2020a).…”

“…It should be noted that all the OCO‐3 and OCO‐2 L2 products used in this work were filtered through their corresponding quality flags for each XCO 2 sounding with “xco2_quality_flag” equal 0 (good) and that each SIF sounding with “Quality_Flag” equal 0 (best quality and cloudless), to efficiently eliminate the impact of low‐quality data on the following investigations (as shown in Figure 1 which also summarizes the procedure of this study). The OCO‐3 L2 XCO 2 and SIF products have demonstrated promising performance in comparison with corresponding OCO‐2 products (Taylor et al., 2020, 2023), and they have been used widely in previous research (Chevallier et al., 2022; Kiel et al., 2021; Wu et al., 2022; Z. Zhang et al., 2023b).…”

“…There is a slight variation in the results between the different OCO observation modes, with the bias of 1.39 ppm for the SAM mode data being larger than that of 0.91 ppm for the land nadir mode data (Figure S1 in Supporting Information ). Overall, the satellite‐derived XCO 2 data with deviation of approximately <0.25% were considered acceptable for further scientific analysis (Miller et al., 2007; Taylor et al., 2023).…”