Development of cloud monitoring system for cosmic microwave background observations

The cloud between a ground-based telescope and the sky signal, such as cosmic microwave background, can distort the measured temperature signal from the sky, or even obstruct it. We developed a cloud monitoring system for cosmic microwave background observations. This system uses infrared imaging sensors; therefore, it is independent of visible legibility and the monitoring is capable day and night. The sensors and their controller are protected by a weather-proof container and able to be installed at the bare ground exposed to the external environment. By our system, information of sky area covered by clouds can be provided for ground-based telescopes by 0. 37 ^∘ resolution. The design and fabrication of the cloud monitoring system as well as its initial performance are described.