Calibration of CRL all-sky imagers using an integrating sphere

Abstract

As part of an international collaboration with the Geophysical Institute of the University of Alaska, two all-sky imagers (CRL-ASIs) have been developed. A sensitivity calibration of the CRL-ASIs was performed using an integrating sphere belonging to the National Institute of Polar Research (NIPR). The two-dimensional sensitivities of the CRL-ASIs produced symmetrical distributions. Using this sensitivity data, airglow/aurora images were converted into two-dimensional distributions of absolute intensity. The sensitivity of the CRL-ASIs was measured for 13 wavelengths between 427.8 nm and 866.5 nm, and the relationship between the sensitivity and the wavelength was investigated for both imagers. The peak sensitivity occurred at about 550 nm.