INVESTIGATIONS OF SOLAR-RADIATION DETECTORS USING A LABORATORY TEST FACILITY FOR SOLAR-RADIATION METEOROLOGICAL INSTRUMENTS

A laboratory test facility for solar radiation detectors has been buil t and is in operation at the Aerological Station of the Swiss Meteorol ogical Institute (SAP/SMI). This installation is conceived as a univer sal test bed for solar radiation exposed meteorological instruments, a nd consists of a commercially available solar simulator, a laser align ment system, a translation mechanism with instrument mounts, and an ad justable projection mirror. The solar simulator produces a well charac terized radiation beam which can be filtered to match the terrestrial or outer space solar spectrum with an irradiance of up to one solar co nstant (1367 Wm-2). The instrument mounts and a HeNe laser beam provid e a precise and easy alignment of the reference and the test instrumen ts in the radiation beam, allowing for incident angles in the range of 15-degrees-75-degrees. The measurement is based on a comparison of th e response of an active cavity absolute radiometer PMO6 with the signa l of the test instrument. Detailed investigations of the Haenni Solar 111B type heliometer have revealed important irregularities in the sun shine threshold irradiance angular distribution. Measurements performe d with and without the protection glass cover prove the exceedingly hi gh threshold values at large declination angles to be a consequence of enhanced reflections due to the incident angle and inhomogeneities in the glass cover. Very satisfactory results have also been obtained on characterization measurements of pyranometers showing the mean values of the responsivity to be within 0.8% of the calibration values measu red at the world radiation center (WRC) at Davos.