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

摘要

Spectral sky radiance (380–760 nm) is derivedfrom measurements with a hemispherical sky imager (HSI)system. The HSI consists of a commercial compact CCD(charge coupled device) camera equipped with a fish-eyelens and provides hemispherical sky images in three referencebands such as red, green and blue. To obtain the spectralsky radiance from these images, non-linear regressionfunctions for various sky conditions have been derived. Thecamera-based spectral sky radiance was validated using spectralsky radiance measured with a CCD spectroradiometer.The spectral sky radiance for complete distribution over thehemisphere between both instruments deviates by less than20% at 500 nm for all sky conditions and for zenith anglesless than 80 . The reconstructed spectra of the wavelengths380–760 nm between both instruments at various directionsdeviate by less than 20% for all sky conditions.