The reflexion coefficients of ionospheric regions.

Abstract

In a recent communication to the Society, Watson Watt, Wilkins and Bowen (1937) have described the results of an ionospheric investigation conducted by means of radio wave reflexion which they have interpreted as demonstrating the existence of four or more highly reflecting strata in the lower atmosphere, about 10 km. above ground level. These results and their interpretation are naturally of great interest to those whose field of investigation has been the ionospheric regions at greater heights; for, as the authors of (I) state, their own findings “must modify the detailed discussion of ionospheric soundings effected with sounding waves which have had to traverse these highly reflecting strata”. Moreover, if the high reflexion coefficients estimated for these low-lying strata are correct, even as regards order of magnitude only, it is immediately obvious that our ideas concerning the travel of wireless waves to great distances require radical revision, for, since 1926, it has been customary to regard such communication as generally being effected either by way of Region E in the case of long waves, or by way of Region F in the case of the shorter waves. It can, further, be asserted that current explanations of such phenomena are in such close agreement with the results of what is now known of the structure of the ionosphere at levels of 90 km. and above, that any evidence not in harmony with these accepted relations must be accorded the closest scrutiny. The experimental observations of Colwell and Friend (1936) and of the authors of (I) (1937) concerning the return of radio waves from low levels in the atmosphere are of the greatest scientific importance and, immediately they were announced, investigations were begun here in Cambridge to see if we could confirm them. It was desired especially to ascertain in this connexion how far the existence of such lowlying reflecting strata influenced the interpretation of the vast amount of observational work already carried out in various parts of the world on radio reflexion at higher levels.