SPN1 Sunshine Pyranometer

The SPN1 measures the amount of direct plus diffuse and diffuse incoming visible radiation simultaneously, from which estimates of cloudiness or hours of direct sunlight may be obtained.  ISF has two that are deployed occasionally.  During METCRAX, an SPN1 inside the Winslow, AZ meteor crater reported direct+diffuse levels less than diffuse at dawn when direct sun was blocked by the crater walls.  This odd behaviour was never explained.