Hourly trends of nighttime cloud cover observations in Chiba using a ground-based digital camera

摘要

Digital cameras with and without infrared (IR) filters are used to take images of the sky at nighttime every 5 minutes atthe Center for Environmental Remote Sensing (CEReS) in Chiba University for the purpose of quantifying cloud cover overChiba. The results show that by applying a threshold pixel value, clear sky pixel values can be separated from cloudy sky pixelvalue. Temporal variation of average hourly cloud cover values show that summer months exhibit high cloud cover (> 40%) and adecreasing trend of cloud cover is observed at nighttime.