Validation of radiative transfer approaches for all-sky atmospheres using IASI infrared spectra

We present an evaluation of radiative transfer model performance in all-sky atmospheric conditions through comparisons with infrared radiances measured by the Infrared Atmospheric Sounding Interferometer (IASI). The study focuses on testing different forward modeling approaches within the σ-IASI/f2n framework, including a novel linear-in-T approximation. Simulated top-of-atmosphere radiances are produced under a range of atmospheric scenarios (including both clear-sky and cloudy-sky conditions) assuming collocated ECMWF analysis as state vector using various configurations of the σ-IASI/f2n code: with and without the linear-in-T approximation, and with either the Chou or Tang cloud treatment. These simulations are compared against collocated IASI observations to assess the spectral accuracy of each configuration. The goal of this study is to quantify how modeling assumptions affect the representation of all-sky infrared spectra, particularly under cloud-contaminated conditions where accurate radiative transfer is most challenging. While the retrieval of cloud properties is supported within the modeling framework, this work focuses primarily on the forward model as a critical step for possible retrieval applications. By systematically evaluating model behavior in all-sky scenes, this study contributes to the refinement of radiative transfer tools for use in climate research, satellite data analysis, and atmospheric remote sensing applications.