Global Terrestrial Ecosystem Carbon Flux Inferred from TanSat XCO ₂ Retrievals

Abstract

TanSat is China’s first greenhouse gases observing satellite. In recent years, substantial progresses have been achieved on retrieving column-averaged CO2 dry air mole fraction (XCO2). However, relatively few attempts have been made to estimate terrestrial net ecosystem exchange (NEE) using TanSat XCO2 retrievals. In this study, based on the GEOS-Chem 4D-Var data assimilation system, we infer the global NEE from April 2017 to March 2018 using TanSat XCO2. The inversion estimates global NEE at −3.46 PgC yr-1, evidently higher than prior estimate and giving rise to an improved estimate of global atmospheric CO2 growth rate. Regionally, our inversion greatly increases the carbon uptakes in northern mid-to-high latitudes and significantly enhances the carbon releases in tropical and southern lands, especially in Africa and India peninsula. The increase of posterior sinks in northern lands is mainly attributed to the decreased carbon release during the nongrowing season, and the decrease of carbon uptakes in tropical and southern lands basically occurs throughout the year. Evaluations against independent CO2 observations and comparison with previous estimates indicate that although the land sinks in the northern middle latitudes and southern temperate regions are improved to a certain extent, they are obviously overestimated in northern high latitudes and underestimated in tropical lands (mainly northern Africa), respectively. These results suggest that TanSat XCO2 retrievals may have systematic negative biases in northern high latitudes and large positive biases over northern Africa, and further efforts are required to remove bias in these regions for better estimates of global and regional NEE.

Constraining China's land carbon sink from emerging satellite CO2 observations: Progress and challenges

“…Two studies (Wang, Jiang, et al, 2022; Yang, Liu, Feng, et al, 2021) have used the retrieval products for 15 months (Yang, Liu, Boesch, et al, 2021) released by the TanSat group to estimate the global and regional land carbon sink by atmospheric inversion. The inversion estimates of global land carbon flux using TanSat XCO 2 retrievals are generally consistent with the inversions using OCO‐2 retrievals.…”

“…Two studies (Wang, Jiang, et al, 2022;Yang, Liu, Feng, et al, 2021) have used the retrieval products for 15 months (Yang, Liu, Boesch, et al, 2021) released by the TanSat group to estimate the global and regional land carbon sink by atmospheric inversion.…”

“…The inversion estimates of global land carbon flux using TanSat XCO 2 retrievals are generally consistent with the inversions using OCO‐2 retrievals. The inversion estimate of China's carbon land sink (Wang, Jiang, et al, 2022), in which GEOS‐Chem was used as atmospheric transport model, is 0.95 Pg C year −1 , within the ensemble of those based on OCO‐2 retrievals. These results provide first evidence that the TanSat platform obtained reasonable XCO 2 data and it could be promising to use such data to constrain carbon fluxes over northern middle latitudes.…”

A Calibration Method for Large-Footprint Full-Waveform Airborne Laser Altimeter without a Calibration Field

“…In November 2019, the GF-7 satellite was launched with two linear system laser altimeters, which opened the exploration of full-waveform large-footprint laser altimetry in China [17][18][19][20]. Recently, the Terrestrial Ecosystem Carbon Inventory Satellite, dedicated to forest resource surveys, has been launched, carrying a five-beam lidar load for acquiring high-precision three-dimensional structures of forests at large footprints [21,22]. To verify the performance of the laser altimeter system, the National Forestry and Grassland Administration, together with scientific research institutes, carried out the development and flight testing of an airborne large-footprint laser altimeter system.…”

A Robust Estimate of Continental‐Scale Terrestrial Carbon Sinks Using GOSAT XCO2 Retrievals

“…Remotesensing-based CO 2 measurements provide global coverage with high spatial resolutions (Baker et al, 2010). Many studies have estimated regional carbon sources and sinks using column averaged dry air mole fractions of CO 2 (XCO 2 ) from GOSAT and OCO-2 satellites (Baker et al, 2010;Basu et al, 2013;Byrne et al, 2020;Chevallier et al, 2014Chevallier et al, , 2019Crowell et al, 2019;Deng et al, 2014;Houweling et al, 2015;Jiang et al, 2021;Wang et al, 2018Wang et al, , 2019Wang et al, , 2022, boosting the possibility of better constraining the carbon cycle at finer spatial scale (Byrne et al, 2019). The GOSAT intercomparison study from Houweling et al (2015) found that robust estimates could be obtained at large global scale, but at the TRANSCOM regions, the different inversions differed significantly.…”