In the years since the pioneering efforts of Sir Edward Appleton, M. A.
F. Barnett, G. Breit, and M. A. Thve, many radio techniques have been
employed to investigate the terrestrial ionosphere. The purposes of this
book are to exam- ine the basic physical interaction process of radio
waves with the ionosphere, scrutinize each of the radio techniques
currently in use, and describe the elements of each technique, as well
as assess their capabilities and limitations. I have included some of
the history of each technique, since we often tend to forget the efforts
of the "pioneers". The interaction of radio waves with the terrestrial
ionosphere has been described in considerable detail in several
"classic" treatments, e.g., Ratcliffe (1959), Al'pert (1963), Budden
(1961) and Davies (1965), Rishbeth and e.g., Flock (1979), Davies
Garriott (1969), and in other more recent books, (1990), Hargreaves
(1979), and Budden (1985). A few of the radio techniques have been
described by Hargreaves (1979) and a book by Giraud and Petit (1978) has
also included discussion of several of the techniques. The "WITS"
handbook No. 2 (1989) also contains description of several radio
techniques.