High precision calibration of a Sun photometer using Langley plots performed at Jungfraujoch (3580 m) and standard irradiance lamps

A six channel Sun photometer has been calibrated by means of two different methods: Langley plots and standard irradiance lamps. A four month calibration campaign was carried out at the high mountain site Jungfraujoch (3580 m a.s.l.) in the Swiss Alps. Repeated calibration of the Sun photometer by means of standard irradiance lamps was performed at the WRC in Davos. The intercomparison of both methods range from perfect agreement to a deviation of 4% for the different channels. A discussion of the errors introduced by both methods leads to the conclusion that the Langley-plot calibration when performed under very clear atmospheric conditions is superior