Absorption of terahertz radiation by atmospheric water vapor is a serious impediment for radio astronomy and for long-distance communications. Transmission in the THz regime is dependent almost exclusively on atmospheric precipitable water vapor (PWV). Though much of the Earth has PWV that is too high for good transmission above 200 GHz, there are a number of dry sites with very low attenuation. We performed a global analysis of PWV with high-resolution measurements from the Moderate Resolution Imaging Spectrometer (MODIS) on two NASA Earth Observing System (EOS) satellites over the year of 2011. We determined PWV and cloud cover distributions and then developed a model to find transmission and atmospheric radiance as well as necessary integration times in the various windows. We produced global maps over the common THz windows for astronomical and satellite communications scenarios. Notably, we show that, up through 1 THz, systems could be built in excellent sites of Chile, Greenland, and the Tibetan Plateau, while Antarctic performance is good to 1.6 THz. For a ground-to-space communication link up through 847 GHz, we found several sites in the Continental United States where mean atmospheric attenuation is less than 40 dB, which is not an insurmountable challenge for a link. © 2013 IEEE.

© 2015 IEEE. While terahertz (THz) communication systems, operating from 100 GHz to 1 THz, have the potential to exploit wide swaths of unused spectrum for ultra-high bitrate communication, there are significant challenges. Particularly, the strong absorption of water vapor can result in very high atmospheric attenuation. We modeled a ground to geostationary satellite link and found that using large aperture THz stations, patterned after the 12.5 m Atacama Large Microwave Array dish and the 3.5 m Herschel Space Observatory optics, worst 10th percentile data rates in excess of one terabit per second in the THz bands are possible. The key is to site ground stations in dry regions. We locate these by coupling our link model, which selects optimum modulation and carrier bandwidth, with global, high-resolution satellite water vapor measurements. We present detailed maps showing modeled link performance over the surface of the Earth. Smaller apertures on aircraft and balloons are also able to exceed 1 terabit/second due to their location above nearly all water vapor. Compared to free-space optical links, evidence suggests THz systems are superior where fog, cloud cover and clear-air turbulence are of concern.