Pilot Study on Estimation of Upward Flux by Luminance Distribution of Night Sky Luminance

The upward flux from the cities may cause sky glow. The purpose of our study is to calculate the upward flux from luminance distribution of night sky viewed from ground level on cloudy days. In this study the clouds’ heights and the reflectance of the clouds are used as well as luminance distribution of the night sky to calculate the upward flux. The reflectance of the cloud is presumed from the cloud type which is determined from the cloud model of Liou’s study referring to cloud heights and radiant temperature. An experiment is carried out using a scale model to verify the precision of the method. It is confirmed that upward flux can be almost precisely calculated by this method. The Tokyo metropolitan area is divided using grids (2.5 km×2.5 km) and the upward luminous flux of each area is calculated. A set of six measurement points is chosen which can measure the upward luminous flux from all light-emitting areas, and each measurement point must not have any obstacles in the viewing angle of the cloud infrared radiometer. The results show that 5 lm/m2 of upward luminous flux was emitted from the center of Tokyo. The distribution of the electricity wastage emitted to the sky was also illustrated.