Abstract

As a result of sky radiance anisotropy, significant errors spoil diffuse solar irradiance data obtained by means of noncosine-true instruments, which happens in spite of knowledge of the relative cosine response. To reduce these errors we recommend a method that involves an additional measurement of diffuse irradiance from a horizon band. The efficiency of the so-called double-measurement method is found to be optimum for a 25° horizon band elevation. We confirm the feasibility of the method with relevance tests that use diffuse solar spectral measurements carried out on cloudless skies by means of an UV spectroradiometer.

© 1996 Optical Society of America

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