Articles | Volume 7, issue 7
Atmos. Meas. Tech., 7, 2137–2146, 2014
Atmos. Meas. Tech., 7, 2137–2146, 2014

Research article 16 Jul 2014

Research article | 16 Jul 2014

Validation of spectral sky radiance derived from all-sky camera images – a case study

K. Tohsing, M. Schrempf, S. Riechelmann, and G. Seckmeyer K. Tohsing et al.
  • Institut für Meteorologie und Klimatologie, Leibniz Universität Hannover, Herrenhäuser Straße 2, Hanover 30419, Germany

Abstract. Spectral sky radiance (380–760 nm) is derived from measurements with a hemispherical sky imager (HSI) system. The HSI consists of a commercial compact CCD (charge coupled device) camera equipped with a fish-eye lens and provides hemispherical sky images in three reference bands such as red, green and blue. To obtain the spectral sky radiance from these images, non-linear regression functions for various sky conditions have been derived. The camera-based spectral sky radiance was validated using spectral sky radiance measured with a CCD spectroradiometer. The spectral sky radiance for complete distribution over the hemisphere between both instruments deviates by less than 20% at 500 nm for all sky conditions and for zenith angles less than 80°. The reconstructed spectra of the wavelengths 380–760 nm between both instruments at various directions deviate by less than 20% for all sky conditions.