The Boltwood cloud sensor is made by Diffraction Limited and measures the amount of cloud cover by comparing the temperature of the sky to the ambient temperature at ground level. The sensor measure the sky temperature in the 8 to 14 micron infrared radiation band. A large difference between the ambient temperature at ground level and the sky temperature indicates clear skies. Conversely, a small temperature difference indicates that the sky is cloudy because the cloud cover appears “warmer” to the sensor than a clear sky.
The cloud sensor is also mounted on the weather telemetry pole and is directly wired to the DarkCloud weather server. Real time weather information from the cloud sensor is updated to this website every 5 minutes.
The cloud sensor also measures moisture and can detect even a few drops of rain. When rain is detected, the cloud monitor sends a signal to the Ace Smart Dome control unit to close the dome if it is open.
The sensor also measures wind speed, humidity and daylight. If any of these values exceeed predetermined maximum levels, the cloud monitior sends a signal to close the dome. For example, when the sun rises, the cloud monitor will detect daylight and will request the Ace Smart Dome to close the dome.
Finally, the cloud monitor, produces a time lapse chart showing the sky conditions over the last few hours. The chart to the right is a current real-time time lapse chart showing the changing cloud conditions over the last 12 hours.
The top part of the chart indicates cloud conditions. White means it is clear, yellow means cloudy and red means very cloudy. Blue means that rain or moisture is present.
The Astronomical Weather page shows a continual real-time cloud monitor chart.
The DarkCloud weather server post explains how the cloud monitor provides information to the weather server and this web page.