Development of a Moon Photometer Based on the Prede Sky-Radiometer to Measure Aerosol Optical Thickness During Polar Night Seasons

Sun photometry to obtain the aerosol optical thickness (AOT) needs the sun. In the polar region, the effective measurements of AOTs by sun photometry are limited during the season of the midnight sun. The moon instead of the sun must be another source of light during the polar night season. A moon photometer was developed by modification of the Prede POM-02 Sky-radiometer to measure the spectral lunar irradiance in the polar region. The original POM-02 model has an electric dynamic range of 10⁹ to measure both of direct- and circum-solar radiation. The electronics of POM-02 was upgraded to include a 10¹¹ dynamic range for the capability to measure the direct lunar irradiance at the visible range as well as the sun and sky measurements with a single instrument. A CMOS-based moon sensor was newly developed to track the moon as well as the sun. The position of the moon/sun is determined with accuracy of better than 0.01° by a real-time processing system using the CMOS imager. Test measurements with the modified POM-02 instrument under the full moon condition showed a good performance for lunar photometry to obtain the spectral AOT.