Ionospheric investigations using the sweep-frequency pulse technique at oblique incidence

This paper describes the prese nt state of obliqu e-in cidencc in vestigaLion s of Lhc ionosphere, using the sweep-frequency pulse technique, with sp ecial reference to the work canied out. at tl?e ~ ational Bureau of Standards. After a short r eview of the publi hed li terature, obhque-lllCldence sweeps are presented showing the diurnal a nd seasonal variations Oll two east-west paths of lengths 1,150 kilometers and 2,370 kilom eters. The discrep ancies between observed and calculated maximum usable frequencies are presented for both p ath s and then various phenomena of interest are shown . Finally, the a bove phenome na are disc ussed in the light of existing knowledge and theory and, in particula r, it i shown that the di screpa ncies between observed and calculated maximum usable fr equ e nci es are unlikely to be caused by magn etoionic d eviation of the ray.