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
Original Manuscript: June 28, 1995
Revised Manuscript: February 16, 1996
Published: October 20, 1996
A. de La Casinière, T. Cabot, A. I. Bokoye, and J. L. Pinedo, "Improvement of diffuse solar irradiance measurements with noncosine instruments," Appl. Opt. 35, 6069-6075 (1996)