Satellites are becoming increasingly important to track global carbon cycle. China is preparing to launch its next-generation carbon monitoring satellite, TanSat-2, which is designed to provide global and regional observations of column-averaged carbon dioxide (CO₂) and methane (CH₄).

Atmospheric CO₂ observations contain signals from both human activities and carbon exchanged between atmosphere and terrestrial ecosystems, making it difficult for satellite-based carbon monitoring to determine how much of the observed CO₂ originates from fossil fuel emissions and how much is associated with ecosystem carbon uptake and release.

In a study published in Advances in Atmospheric Sciences, researchers from the Institute of Atmospheric Physics of the Chinese Academy of Sciences, along with UK researchers, investigated the potential of TanSat-2 observations for assessing anthropogenic carbon emissions and ecosystem carbon sinks.

Researchers developed a carbon flux inversion approach combining atmospheric CO₂ measurements with solar-induced chlorophyll fluorescence (SIF). The measurements can simultaneously constrain net primary productivity (NPP) and fossil fuel combustion emissions (FF).

To further separate natural ecosystem carbon fluxes and fossil fuel emissions, researchers applied empirical orthogonal function analysis to prior NPP and FF inventories, which identified their dominant spatial and temporal patterns while reducing the number of variables that need to be optimized in the inversion.

Using observing system simulation experiments, researchers found that TanSat-2 CO₂ and SIF observations lead to an NPP error reduction of up to 95% over Siberia and the Amazon, and to error reductions of about 80% for FF emissions over Siberia, North Asia, the United States, and South Africa, if measurement bias can be eliminated.

However, even small systematic biases in satellite-derived column-averaged dry-air mole fractions of CO₂ (XCO₂) can distort inferred CO₂ sources and sinks, or even lead to their misattribution. Such biases can ultimately compromise the reliability of carbon flux estimates. It is important to identify and correct systematic errors in satellite retrievals.

Moreover, researchers investigated whether increasing TanSat-2's cross-track swath width can strengthen its carbon-monitoring capability. They found that a wider observational swath improves the robustness of CO₂ flux estimates. An error-matrix analysis framework was developed to help evaluate observing strategies and support the design and optimization of carbon-monitoring satellite missions.

"Reliable monitoring of carbon fluxes requires the integration of satellite, ground-based, airborne, and in situ observations, which will be essential for building a more accurate and comprehensive picture of Earth's carbon sources and sinks," said Dr. YANG Dongxu from the Institute of Atmospheric Physics, one of the authors of this study.