Reflection of radio waves by the lower ionosphere at night

The available experimental data relating to the height distribution of electron concentration at night has shown the presence of a pronounced ledge of ionisation between about 80 and 90km, and thin layers at greater heights. Idealised models of the electron-density distribution have been constructed, some of which incorporate these two features. The propagation parameters for vertically polarised radiowaves, in the frequency range 4¿1000kHz, incident on these models, have been computed using a full-wave integration procedure. These computations have been carried out for angles of incidence of 30° and 80°, at various azimuths, and for middle and low latitudes. Particular attention is paid to the polarisation conditions of the reflected waves, and special emphasis is given to the results for frequencies near 10 and 100kHz, of interest for radio navigational aids, and near 300kHz, which are important for broadcasting.