Calibration of all-sky cameras and tilting-photometers using an integrating-sphere and a spectrometer

Abstract

We report calibration of the optical instruments of the Optical Mesosphere Thermosphere Imagers (OMTI) using facilities at the National Institute of Polar Research. OMTI has been developed to investigate dynamics of the upper atmosphere through nocturnal airglow emissions. OMTI consist of an imaging Fabry-Perot interferometer, three all-sky cooled-CCD cameras, three tilting-photometers, and a spectral airglow temperature imager (SATI). The all-sky cameras and the photometers have been calibrated using a 2-m integrating-sphere and a spectrometer. Absolute sensitivity and image-flattening data are obtained together with filter transmission functions. Inhomogeneity of transmission function on the filter surface is found from the calibration using the spectrometer. We also find that filters with highly-flattened image-quality surfaces may cause serious Newton's Ring pattern on final images. Examples of the data are shown for the cameras and the photometers based on the airglow observation at Shigaraki (35°N, 136°E), Japan.