The ionosphere of the Earth has been actively studied since the 1920's,
following the discovery of ground radio-sounding. By means of this
method results were ohtained by an international network of ionospheric
stations, in particular, by the successful implementation of a number of
rigorously planned international scientific research programs, '"
enabling the collection of extensive experimental material on some of
the most important parameters of the ionosphere - the critical
freLjuencies of E-, Fl- and F2-layers. Comprehensive analyses of these
observation data give a fairly complete picture of the various changes
taking place in the principal ionospheric layers at different points on
our globe. Another important aspect of the study of the ionosphere,
which has been in progress for the past three decades, is an extensive
program of in situ determinations of the various physical parameters -
first using rockets, and subsequently artificial satellites. The data
thus obtained on the principal ionizing agent - short-wave solar
radiation - and on the physical conditions prevailing in the upper
atmosphere and in the ionosphere at different altitudes, allow the
proposal of a self-consistent mechanism of ionosphere formation. A
general outline of the theory of ionosphere formation at different
altitudes is now complete. Its application to specific cases, dependent
on a more accurate determination of input parameters to give solutions
valid for a definite set of conditions etc., is yet to be accomplished.
The use of artificial satellites in cosmic research yielded abundant
scientific data.
