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. Shortwave (SW) fluxes estimated from broadband radiometry rely onempirically gathered and hemispherically resolved fields of outgoingtop-of-atmosphere (TOA) radiances. This study aims to provide moreaccurate and precise fields of TOA SW radiances reflected from cloudsover ocean by introducing a novel semiphysical model predictingradiances per narrow sun-observer geometry. This model wasstatistically trained using CERES-measured radiances paired withMODIS-retrieved cloud parameters as well as reanalysis-basedgeophysical parameters. By using radiative transfer approximations asa framework to ingest the above parameters, the new approach incorporatescloud-top effective radius and above-cloud water vapor in addition totraditionally used cloud optical depth, cloud fraction, cloud phase,and surface wind speed. A two-stream cloud albedo – serving tostatistically incorporate cloud optical thickness and cloud-topeffective radius – and Cox–Munk ocean reflectance were used todescribe an albedo over each CERES footprint. Effective-radius-dependent asymmetry parameters were obtained empirically andseparately for each viewing-illumination geometry. A simple equationof radiative transfer, with this albedo and attenuating above-cloudwater vapor as inputs, was used in its log-linear form to allow forstatistical optimization. We identified the two-stream functionalform that minimized radiance residuals calculated against CERESobservations and outperformed the state-of-the-art approach for mostobserver geometries outside the sun-glint and solar zenith anglesbetween 20 and 70∘, reducing the median SDof radiance residuals per solar geometry by up to 13.2 % forliquid clouds, 1.9 % for ice clouds, and 35.8 % forfootprints containing both cloud phases. Geometries affected bysun glint (constituting between 10 % and 1 % of thediscretized upward hemisphere for solar zenith angles of 20 and70∘, respectively), however, often showed weakerperformance when handled with the new approach and had increasedresiduals by as much as 60 % compared to the state-of-the-artapproach. Overall, uncertainties were reduced for liquid-phase andmixed-phase footprints by 5.76 % and 10.81 %,respectively, while uncertainties for ice-phase footprints increasedby 0.34 %. Tested for a variety of scenes, we furtherdemonstrated the plausibility of scene-wise predicted radiancefields. This new approach may prove useful when employed in angulardistribution models and may result in improved flux estimates, inparticular dealing with clouds characterized by small or largedroplet/crystal sizes.

Using two-stream theory to capture fluctuations of satellite-perceived TOA SW radiances reflected from clouds over ocean