Atmospheric EHF window transparencies near 35, 90, 140 and 220 GHz

Transparency of the four atmospheric extremely high frequency (EHF) window ranges located around 35, 90, 140, and 220 GHz is obscured by precipitation (rain, wet snow), by suspended particles (fog, cloud, haze, dust), and by water vapor. An assessment is made of the quantitative picture (i.e., models versus experiments and theory.), upon which estimations for general radio path behavior can be based. Useful models are provided for calculating attenuation based upon measurable meteorological variables: rain rate, liquid water content, humidity, temperature, and pressure. Information currently available is not yet complete enough to provide accurate predictions under all climatological conditions. Emphasis is on recent advances in formulating the physical basis for modeling transparency and on a discussion of some of the principal remaining uncertainties.