RF MODULE

Night side
Earth surface
Ionosphere boundary
Day side
Figure 2-7: The model geometry is in blue. The brown area representing the Earth is
included only for illustration. The cavity thickness is 300 km on the night side and 100 km
on the day side.
The Earth’s ionosphere is composed of different layers that are rather characterized by
local maxima in electron density than distinct layers. The most important layers
ordered from the inner are referred to as the D, E, F1, and F2 layers. The height of
the different layers depends on ionization, which is due to sun radiation, while at night
time some of the layers are reduced or even disappear. On the day side of the Earth,
the height of the cavity between the inner layer of the ionosphere and the Earth is
approximately 100 km, while on the night side, the height is about 300 km. Most of
the radiation that ionizes the upper layers is absorbed so that below the D layer,
negligible ionization occurs. The conductivity therefore decreases rapidly toward zero.
The conductivity profile in the cavity between the Earth surface and the innermost
layer of the ionosphere varies over time with several different parameters. Furthermore
the profile is not linear. This model, however, assumes a fixed value at the upper
boundary of the cavity that decreases linearly to zero at the Earth’s surface.
CALCULATING THE SCHUMANN RESONANCE FREQUENCIES | 43