Joint retrieval of aerosols, XCO2, and XCH4 from polarimetric and spectrometric data using GRASP

Accurately characterizing atmospheric aerosols remains a primary challenge in achieving high precision in satellite retrievals of XCO2 and XCH4. While Shortwave Infrared (SWIR) spectral bands provide optimal sensitivity to greenhouse gas concentrations, Multi-Angular Polarimetric (MAP) measurements represent the most advanced approach for constraining aerosol and surface properties. Consequently, upcoming Copernicus missions, such as CO2M and MetOp-SG (hosting Sentinel-5/UVNS spectrometer and 3MI polarimeter), are equipped to exploit the synergy between these measurement types.

In this context, we present  an open-source, full-physics retrieval algorithm for GHG retrievals  to demonstrate its capabilities through the synergistic inversion of SWIR spectrometric (i.e., S5-UVNS and CO2M/CO2I spectrometers) and multi-angle polarimetric data (3MI and CO2M/MAP). The core of this retrieval approach is the Generalized Retrieval of Atmosphere and Surface Properties (GRASP) algorithm (Dubovik et al., 2021). GRASP relies on rigorous radiative transfer modeling and statistically optimized fitting (Multi-Term Least Squares) to process a wide range of optical instruments. While originally designed for MAP applications (e.g., POLDER, 3MI; Li et al., 2019; Chen et al., 2020), the approach has been extended to combine MAP and SWIR spectrometric measurements, accounting for gas absorption, offering a simultaneous retrieval of detailed aerosol microphysics and surface properties alongside with columnar XCO2 and XCH4.

In this work the GRASP algorithm has been successfully adapted to perform gas retrievals, allowing for the robust simultaneous inversion of aerosol properties and XCO2 and XCH4. We demonstrate the capabilities of this new GRASP inversion scheme through synthetic datasets representing the Sentinel-5+3MI and CO2M synergies. These synthetic experiments highlight that incorporating MAP measurements yields significantly improved accuracy for XCO2 and XCH4 compared to standalone spectrometer retrievals. This project has been funded through the OPERA-S5 project (OPEn platform for the Retrieval of Aerosol and CO2 from S5), an ESA-funded initiative developed by GRASP SAS company and SRON. This development lays the groundwork for the operational processing of future multi-sensor satellite missions, offering a powerful tool for enhanced global monitoring of greenhouse gases and aerosol interactions.

 

 

 

References

Chen, C., Dubovik, O., Fuertes, D., Litvinov, P., Lapyonok, T., Lopatin, A., ... & Federspiel, C. (2020). Validation of GRASP algorithm product from POLDER/PARASOL data and assessment of multi-angular polarimetry potential for aerosol monitoring. Earth System Science Data Discussions, 2020, 1-108.

Dubovik, O., D. Fuertes, P. Litvinov, et al., “A Comprehensive Description of Multi- Term LSM for Applying Multiple a Priori Constraints in Problems of Atmospheric Remote Sensing: GRASP Algorithm, Concept, and Ap-plications”, Front. Remote Sens. 2:706851. doi: 10.3389/frsen.2021.706851, 2021.

Li, Lei; Derimian, Yevgeny; Chen, Cheng; Zhang, Xindan; Che, Huizheng; Schuster, Gregory L.; Fuertes, David; Litvinov, Pavel; Lapyonok, Tatyana; Lopatin, Anton; Matar, Christian; Ducos, Fabrice; Karol, Yana; Torres, Benjamin; Gui, Ke; Zheng, Yu; Liang, Yuanxin; Lei, Yadong; Zhu, Jibiao; Zhang, Lei; Zhong, Junting; Zhang, Xiaoye; Dubovik, Oleg Climatology of aerosol component concentrations derived from multi-angular polarimetric POLDER-3 observations using GRASP algorithm. Earth Syst. Sci. Data, vol. 14, no. 7, pp. 3439–3469, 2022, ISSN: 1866-3516.