Tropospheric scatter

Tropospheric scatter, also called troposcatter, is a method of long-distance microwave radio communication that exploits a genuine atmospheric phenomenon: as a narrow beam of UHF or SHF radio waves is aimed just above the horizon, some of its energy is randomly scattered by the upper layers of the troposphere and redirected back down toward the Earth's surface, letting a receiving station well beyond the normal line of sight pick up the signal. The technique can carry a usable signal over distances of 500 kilometers or more, depending on frequency, equipment, terrain and climate.