skyWATCH

This is the landing page of the skyWATCH server. Find out more about the skyWATCH devices by reading the skyWATCH all-sky camera introduction.

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About cloud coverage

The cloud coverage figure shown on the meteo info page is derived from the readings of the infra-red temperature sensor. The Swinbank formula provides an ad hoc expression for the power radiated by the night sky. A modified version of this formula from Goforth et al. is $$P_{\text{thermal}} = (1+KC^2)8.78\times 10^{-13}\,T^{5.852}\,{RH}^{0.07195}$$ where

• $K$ is a scale factor based on cloud height, ranging from 0.34 for very low clouds to 0.06 for very high clouds,
• $C$ is the fraction of the sky covered by clouds,
• $T$ is the surface temperature, in kelvins,
• $RH$ is the surface relative humidity, as a percentage (e.g., $RH$ would be 25 in the case of 25% relative humidity), and
• $P_{\text{thermal}}$ is the night sky radiation, in watts per square meter.