TC 9-64 _________________________________________________________________________
2-44. The discussion of electromagnetic wave propagation is concerned
mainly with the properties and effects of the medium located between the
transmitting antenna and the receiving antenna. While radio waves traveling
in free space have little outside influence affecting them, radio waves
traveling within the earth's atmosphere are affected by varying conditions.
The influence exerted on radio waves by the earth's atmosphere adds many
new factors to complicate what at first seems to be a relatively simple
problem. These complications are because of a lack of uniformity within the
earth's atmosphere. Atmospheric conditions vary with changes in height,
geographical location, and even with changes in time (day, night, season, and
year). Knowledge of the composition of the earth's atmosphere is extremely
important for understanding wave propagation.
2-45. The earth's atmosphere is divided into three separate regions, or layers.
the atmosphere are illustrated in figure 2-10.