Institute for Telecommunication Sciences / April 1942
In April of 1942, shortly after the U.S. entry into World War II, the Interdepartmental Radio Propagation Laboratory (IRPL) published its first ionospheric predictions. These predictions on the height and state of the ionospheric layer of the Earth’s atmosphere were used to determine which frequencies and paths would be most effective for radio communication. The ionosphere is made up of shifting plasma that reflects radio waves; it is necessary for radio communication in most situations. Knowing the height and state of the atmospheric layer allows more distant communication with reduced interference. IRPL had been sounding the ionosphere with radio waves and reporting their findings since 1939. By 1942, they could recognize patterns in the data that allowed them to predict the changing state of the atmospheric layer. Since the predictions were used heavily by the military to communicate with troops in the field, the published predictions remained top secret until the end of the war. Publishing ionospheric predictions was one of the most important missions undertaken by IRPL and its successor agencies for many years. ITS no longer publishes ionospheric predictions, but continues to improve telecommunication for everyone by studying the propagation of radio waves and developing new prediction algorithms.