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2026 Contributo in Atti di convegno restricted access

Revisiting Ray-Tracing Algorithm for Future Limb-Scanning Missions

Francesco Pio De Cosmo ; Luca Sgheri

In the forward model for limb-scanning instruments, ray tracing must be accounted for because variations in air refractivity cause the lines of sight to bend from straight paths into curves. The tangent point of a line of sight defined as the minimum height, depends on both the instrument’s nadir angle and the atmospheric state. To achieve reliable tangent point determination, the off-nadir angles must be calibrated to account for Earth’s ellipsoidal geometry and realistic atmospheric conditions sampled by these lines of sight paths. In this study, we improve the ray-tracing algorithm originally developed for MIPAS operational retrievals. The algorithm is applied to more accurately assess the impact of atmospheric variability on the relationship between off-nadir angles and tangent point localization. It also allows us to estimate the smoothing error associated with the coarse horizontal sampling of the MIPAS observation pattern. We used a configuration representative of the proposed CAIRT mission instrument as a case scenario for future instruments such as the STRIVE mission by NASA.

CAIRT, limb scanning, ray tracing
CNR IRIS
2024 Contributo in Atti di convegno restricted access

Developments of the σ-IASI/F2N radiative transfer model: a new linear-in-T approach for accurate treatment of clouds

Masiello G. ; Serio C. ; Liuzzi G. ; Pasquariello P. ; Giosa R. ; Maestri T. ; Martinazzo M. ; Masin F. ; Cassini L. ; Donat F. ; Pelliccia G. P. ; Venafra S. ; Sgheri L. ; De Cosmo F.

The new σ-IASI/F2N radiative transfer model is an advancement of the σ-IASI model, introduced in 2002. It enables rapid simulations of Earth-emitted radiance and Jacobians under various sky conditions and geometries, covering the spectral range of 3-100 μm. Successfully utilized in δ-IASI, the advanced Optimal Estimation tool tailored for the IASI MetOp interferometer, its extension to the Far Infrared (FIR) holds significance for the ESA Earth Explorer FORUM mission, necessitating precise cloud radiative effect treatment, crucial in regions with dense clouds and temperature gradients. The model's update, incorporating the "linear-in-T" correction, addresses these challenges, complementing the "linear-in-tau" approach. Demonstrations highlight its effectiveness in simulating cloud complexities, with the integration of the "linear-in-T" and Tang correction for the computation of cloud radiative effects. The results presented will show that the updated σ-IASI/F2N can treat the overall complexity of clouds effectively and completely, at the same time minimizing biases.

Infrared, Radiative Transfer, Clouds, Satellite, Analytical Derivative, Fast Forward Model, Scattering
CNR IRIS