Models based on basic geometrical properties of several common agricultural screens were developed to describe transmission of direct and diffuse radiation by the screens. Measurements made outdoors with seven different screens validated those models, but showed that the white and clear screens also scatter radiation significantly, such that it is hard to predict total transmission from the models. Empirical trigonometric models fit the results well and can be used to predict transmission of screens based on a straightforward set of measurements.
Transmission of directional radiation by all screens depended on the elevation angle and azimuth of the radiation with respect to the holes of the screens. Dust accumulation during Israel’s rainless summer led to significant reductions in transmission, but the latter recovered after rains.
Diffuse radiation transmission was described adequately by a geometrical model and does not depend on screen orientation, but the enrichment of diffuse radiation below non-black screens, due to scattering, limits the model’s usefulness. Additional work to describe scattering by screen threads is necessary before we will be able to predict screen radiative properties adequately based on screen geometry and composition.
Models based on basic geometrical properties of several common agricultural screens were developed to describe transmission of direct and diffuse radiation by the screens. Measurements made outdoors with seven different screens validated those models, but showed that the white and clear screens also scatter radiation significantly, such that it is hard to predict total transmission from the models. Empirical trigonometric models fit the results well and can be used to predict transmission of screens based on a straightforward set of measurements.
Transmission of directional radiation by all screens depended on the elevation angle and azimuth of the radiation with respect to the holes of the screens. Dust accumulation during Israel’s rainless summer led to significant reductions in transmission, but the latter recovered after rains.
Diffuse radiation transmission was described adequately by a geometrical model and does not depend on screen orientation, but the enrichment of diffuse radiation below non-black screens, due to scattering, limits the model’s usefulness. Additional work to describe scattering by screen threads is necessary before we will be able to predict screen radiative properties adequately based on screen geometry and composition.
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