FIGURE 3.2 Top: Atmospheric windows in the radio spectrum commonly used in the Radio Astronomy Service community. The transmission is appropriate for a site of 400-m elevation and a precipitable water vapor content of 1 mm. Courtesy of Lucy Ziurys, University of Arizona. Bottom: Atmospheric zenith opacity in the radio spectrum commonly used in the Earth Exploration-Satellite Service community. From A.J. Gasiewski and M. Klein, “The Sensitivity of Millimeter and Sub-millimeter Frequencies to Atmospheric Temperature and Water Vapor Variations,” Journal of Geophysical Research-Atmospheres, Vol. 13, pp. 17481-17511, July 16, 2000.