Edward Victor Appleton investigated the ionosphere by measuring how radio signals return from the upper atmosphere. Comparing direct and returning radio waves makes their path difference experimentally accessible and constrains the effective height of the reflecting region.
The response changes with frequency because the atmosphere's free electrons alter electromagnetic propagation. Scanning frequency and observing the returning signals helps distinguish ionized layers and their changing conditions. His Nobel lecture connects these measurements with the physical basis of long-distance radio propagation.[ref]
The Ionosphere by Edward Victor Appleton. Nobel lecture: reflected radio signals, effective heights, critical frequencies and ionized layers
Portrait of Edward Victor Appleton
. Nobel Foundation, portrait dated 1947; individual photographer unspecified. Commons asserts Swedish-photograph public-domain status and additionally records a United States PD-1996/URAA public-domain claim., via Wikimedia Commons. Source. Articles by others on the same topic
Edward Victor Appleton (1892–1965) was a British physicist and Nobel laureate known for his contributions to the field of atmospheric physics, particularly in the study of the ionosphere. He was awarded the Nobel Prize in Physics in 1947 for his investigations of the ionosphere and for his work on the reflection of radio waves from the ionosphere, which had important implications for radio communication.