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Cosine Response Characteristics of Radiometric and Photometric Sensors
Global and diffuse irradiance and illuminance are measured with instruments that are assumed to have true cosine responses. It is known, largely from reports with a limited distribution or by word of mouth, that no instrument is perfect in this regard. This paper reports on measurements of cosine responses for several instrument types and manufacture familiar to the solar radiation measurement community. The measurements were made with an automated cosine response test bench using the same protocol for each instrument. The cosine bench measures with variable angular resolution as fine as 0.25 degrees. The automated rotation is in one plane. A manual rotation allows measurements for other azimuths. 6 refs