Pyranometer, radiation measurement

All radiation measurements have always been carried out and processed on the appropriate international pyrheliometric scale. The instruments are regularly calibrated by comparison with the sun as a source to the national pyrheliometer (AHF of The Eppley) and pyranometer (CM 11 of Kipp and Zonen) standards, participating in the periodically organized international or regional comparisons. They are referred to as the World Radiometric Reference (WRR 1980). 

Pyrheliometer is an instrument that measures only the direct radiation from the solar disk itself, without bouncing off clouds or the atmosphere. Concentrating solar collectors utilize only this part of the total solar radiation. Its measurement gives an indication of the clearness of the sky. The normal incident pyrheliometer (NIP) measures this form of radiation. A tracker, called the equatorial mount, is used to keep the NIP pointed at the sun. The difference between the NIP and the total pyranometer readings is referred to as the diffuse solar radiation. 

Fig. 15. Spectral response of thermopile pyranometer measuring total solar radiation is shown with thick black line. Spectral radiance (brightness) of the sky dome (blue line). The cut-off at 3000 nm means the radiometer will not respond to the infrared sky radiation that peaks at 7000...

Knowledge of the optical properties of materials in relation to the solar spectrum is also important in measuring broadband solar radiation. For instance, a pyranome ter used to monitor total solar radiation for a renewable energy system has a spectral response (due to the special glass dome protecting the detector) that does not respond to the thermal infrared radiation of the sky beyond 3000 nm, as shown in Fig. 15. Flowever, there will be thermal infrared radiation exchanged between the radiometer and the sky dome, which will influence the measurement performance of the pyranometer.9... 

Pyranometer - A device used to measure total incident solar radiation (direct beam, diffuse, and reflected radiation) per unit time per unit area. 

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