Accurately partitioning shortwave (SW) radiation into its visible (VIS) and near-infrared (NIR) spectral components is essential for climate models and radiation budget studies, as it governs how the atmosphere absorbs, scatters, and reflects incoming solar energy. In support of NASA’s Libera mission, this study presents a novel method for deriving VIS and NIR irradiances from SW, VIS, and NIR satellite-based radiance measurements under clear-sky conditions by leveraging satellite-based radiance measurements across SW, VIS, and NIR bands. The method centers on a parameterization of the ratio of anisotropic factors, denoted as β (Eq. 3), which varies significantly with solar zenith angle (SZA), viewing zenith angle (VZA), relative azimuth angle (RAA), and aerosol optical depth (AOD). A polynomial regression model is developed to estimate β for different surface types. By combining the regressed β with the radiance ratio of VIS to NIR, which will be directly observed by Libera, the method partitions total SW irradiance into its VIS and NIR components. Validation against MODTRAN6.0 radiative transfer simulations over forest and desert surfaces demonstrates high fidelity, with discrepancies under 3 W m⁻². The approach performs best at backward scattering angles and exhibits more consistent results over vegetated surfaces than over bright, arid terrain. While initial testing is focused on two surface types, the demonstrated sensitivity of β to key atmospheric and geometric parameters indicates strong potential for extension to a wide range of land cover types and atmospheric conditions. Future work will focus on expanding the method to cloudy scenes, improving the regression model, and cross-validating results with alternative radiative transfer tools and in situ measurements.
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