Development of a flexible module accounting gas absorption in GRASP allowing simultaneous retrieval of gases and aerosols

Accurate modeling of gas absorption is essential for understanding atmospheric radiative transfer and enabling reliable retrievals of atmospheric composition. To address this need, we have developed a new gas computation module into the GRASP (Generalized Retrieval of Atmosphere and Surface Properties, Dubovik et al., 2021) code, extending its capability for simultaneous retrieval of atmospheric gases and aerosols.

The new gas module primarily employs an optimized correlated k-distribution method (Momoi et al., 2022) to efficiently calculate gas absorption optical thickness with high accuracy across a wide spectral range. Additionally, the module supports the line-by-line method as a complementary approach for comparison and validation, ensuring high accuracy and flexibility for a variety of atmospheric scenarios. The implementation of the gas module significantly expands GRASP’s capabilities, making it a more comprehensive tool for simultaneous retrieval of atmospheric gas vertical profiles and aerosol properties. 

Preliminary results regarding the combination of multi-angular polarimeters and SWIR spectrometers (e.g., CO2M, S5 and 3MI) highlight the module's computational efficiency, precision, and adaptability, making it well-suited for operational deployment. Its ability to handle diverse atmospheric scenarios enables the development of advanced retrieval algorithms. Integrating this advanced gas module into GRASP code marks a transformative advancement, enhancing the capacity of remote sensing sensors to monitor aerosol and gases and address environmental challenges effectively.