Posts Tagged ‘radar’

Sir Edward V Appleton (1892-1965) British,


Appleton was an English physicist and Nobel prize winner (1947) who discovered the ionosphere.

In 1924 Appleton began research into the strength of the radio signals received at Cambridge from the BBC station in London. He soon discovered that the strength of the signal was constant during the day but varied during the night, rising and falling in an almost regular manner. He suggested that, at night, the Cambridge apparatus was receiving not one but two waves, one travelling directly and the other being reflected by the atmosphere. The existence of a reflecting layer had first been suggested around forty years earlier by Balfour Stewart. In 1902 Oliver Heaviside and A.E. Kennelly had independently postulated the theory of a conducting layer of the atmosphere: the Kennelly-Heaviside Layer. Following their lead Appleton began a series of experiments, which proved the existence of that layer in the upper atmosphere now called the ionosphere. Moreover, by a slight change of wavelength it was possible to measure the time taken by the waves to travel to the upper atmosphere and back. The position of the reflecting layer was thus identified and its height (60 miles above ground) determined. The method used was what is now called “frequency-modulation radar”. The ionosphere was thus the first “object” detected by radiolocation, and this led to a great development of radio research and to a military invention of the greatest importance in World War II


Further experiments which led to the possibility of round-the-world broadcasting were carried out and in 1926 he discovered a further atmospheric layer 150 miles above ground, higher than the Heaviside Layer and electrically stronger. This layer, named the Appleton Layer after him, reflects short waves round the earth. Three years later Appleton made an expedition to Northern Norway for radio research, studying the Aurora Borealis and in 1931 he published the results of further research on determining the height of reflecting layers of the ionosphere, including the use of a transmitter that sent out “spurts” of radio energy, and the photography of the received echo-signals by cathode ray oscillography.(Ack: Nobelprize.org, BBC.Co.UK-history)

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