the radio waves which are received after reflection from ionosphere are called skywave.
the radio waves which are received after reflection from ionosphere are called skywave.
the radio waves which are received after reflection from ionosphere are called?
skywave
due to the ability of ionized atmospheric gases to refract high frequency (hf, or shortwave) radio waves, the ionosphere can reflect radio waves directed into the sky back toward the earth. radio waves directed at an angle into the sky can return to earth beyond the horizon. this technique, called "skip" or "skywave" propagation, has been used since the 1920s to communicate at international or intercontinental distances. the returning radio waves can reflect off the earth's surface into the sky again, allowing greater ranges to be achieved with multiple hops. this communication method is variable and unreliable, with reception over a given path depending on time of day or night, the seasons, weather, and the 11-year sunspot cycle. during the first half of the 20th century it was widely used for transoceanic telephone and telegraph service, and business and diplomatic communication. due to its relative unreliability, shortwave radio communication has been mostly abandoned by the telecommunications industry, though it remains important for high-latitude communication where satellite-based radio communication is not possible. some broadcasting stations and automated services still use shortwave radio frequencies, as do radio amateur hobbyists for private recreational contacts.
ionosphere
physicists resisted the idea of the reflecting layer for one very good reason; it would require total internal reflection, which in turn would require that the speed of light in the ionosphere would be greater than in the atmosphere below it. since the latter speed is essentially the same as the speed of light in a vacuum (""c""), scientists were unwilling to believe the speed in the ionosphere could be higher. nevertheless, marconi had received signals in newfoundland that were broadcast in england, so clearly there must be "some" mechanism allowing the transmission to reach that far. the paradox was resolved by the discovery that there were two velocities of light, the "phase velocity" and the "group velocity". the phase velocity can in fact be greater than "c", but the group velocity, being capable of transmitting information, cannot, by special relativity, be greater than "c." the phase velocity for radio waves in the ionosphere is indeed greater than "c", and that makes total internal reflection possible, and so the ionosphere can reflect radio waves. the geometric mean of the phase velocity and the group velocity cannot exceed "c", so when the phase velocity goes above "c", the group velocity must go below it.
kennelly–heaviside layer