Abstract: A device for generating a reference value that represents a clear sky condition includes a receiver that receives beacon signals transmitted from a satellite. The device also includes logic that estimates carrier-to-noise levels associated with the beacon signals and uses the estimated carrier-to-noise levels to identify non-clear sky conditions. The logic also calculates the clear sky reference value using a portion of the estimated carrier-to-noise values, where the portion that is used excludes the estimated carrier-to-noise values taken during non-clear sky conditions.