Monitoring Surface Radiation in the Continental United States, in Collaboration with NOAA's SURFRAD SURFace RADiation Budget Measurement Network.
Sterling, VA, site photo

NOTICE: As of 1 Jan. 2015, ISIS network radiation data will be reported at a one-minute frequency.

For background information on the ISIS Network, see:

The NOAA Integrated Surface Irradiance Study (ISIS).A New Surface Radiation Monitoring Program B. B. Hicks, J. J. DeLuisi, D. R. Matt Bulletin of the American Meteorological Society Volume 77, Issue 12 (December 1996) pp. 2857-2864.