Measurement of the elevation angles of arrival of multicomponent h.f. skywaves

Various techniques for the measurement of elevation angles of arrival of oblique-incidence ionospherically propagated HF transmissions using a vertical stack of aerials are reviewed. These include single-mode and two-mode analyses, various wavefront analysis methods and Fourier and maximum-entropy spectral analyses. The methods have been applied to experimental data, and although none is completely successful, the spectral analysis methods generally provided the most realistic solutions. An unexpected result is the finding that both sporadic-E and F modes frequently comprise multiple components with different Doppler frequency shifts and arrival angles.