On a new method for exploring the upper ionosphere

The extensiveness and intensity of the ionization in the region above the height of maximum ionization of the F 2‐layer of the ionosphere is not known. It is shown that measurements of the refraction experienced by radio waves arriving at the Earth after passage through the entire ionosphere can yield information about the uppermost regions of the ionosphere. An expression for the refraction of radio waves which pass through a parabolic‐layer model is derived. This permits a range of frequencies to be specified within which profitable refraction‐measurements can be made. Either the Sun, which emits radio waves in the form of noise, or the Moon, which can be used to return radio waves originating on the Earth, is a suitable extraterrestrial source of radio waves. An experimental technique for measuring refraction is described and discussed.