Radio Observations of the Ionosphere at Oblique Incidence

A description is given of an automatic method of using the radio pulse technique at oblique incidence to investigate the structure of the ionosphere. Sweep frequency photographic records were taken for the path Ottawa–Saskatoon (2355 km.). The records obtained confirm the validity of the theory relating vertical incidence to oblique incidence propagation. Sweeps showing such phenomena as E layer cutoff, transmission of the Pedersen ray, multiple reflections, are shown. It is found that the F1 layer is the important propagating layer rather than the F2 layer under certain conditions. Hence conventional methods of predicting frequencies over long distances require modification in these circumstances.