A NEW SPECTROPHOTOMETER FOR MEASURING ULTRAVIOLET SKY BRIGHTNESS AND DIRECT SOLAR RADIATION.
Final scientific rept. 1 Jan 63-31 Dec 66,
PHYSIKALISCH-METEOROLOGISCHES OBSERVATORIUM DAVOS DAVOS-PLATZ (SWITZERLAND)
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A transportable spectrophotometer for measuring ultraviolet sky brightness and solar radiation from 295 to 400 millimicrons is described. This instrument serves for a study of atmospheric scattering by comparing measured and theoretical values of intensity. Its main components are A double monochromator Zeiss MM 12, a telescope, a photomultiplier enclosed in a cooling box and a mounting for following the sun and scanning the sky according to the astronomical and horizontal system respectively. Neutral attenuation filters are applied to bridge the interval of brightness 100,000 between sun and sky and to adapt the sensitivity to the varying sky brightness. The components of sky brightness polarized parallel and normal to the entrance slit are measured separately. An effective spectral bandwidth between 0.9 and 2.5 millimicrons is normally applied. Mean values of the signal current are measured by means of a Keithley 610 A electrometer and a voltage-to-frequency converter. Photon counting is applied for the lowest levels of intensity. The overall accuracy amounts to plus or minus 7 for intensity and to plus or minus 3 to 5 for the ratio between sky brightness and solar radiation.
- Atmospheric Physics