The mechanism of reflection of radio waves from the anisotropic lower ionosphere with exponential profile has been investigated over a wide frequency range from ELF (extremely low frequency) to LF (low frequency) by means of a full-wave method. The reflection levels deduced from the full-wave study have been compared with those which are analytically obtained from the concept of the modified refractive index for the isotropic ionosphere.

The wave distribution functions (WDFs) have been reconstructed by means of the maximum entropy inversion to the observed spectral matrix composed of the auto- and cross-power spectra among the three field components (Bx, By and Ez) in which the exactly right-handed circular polarization is taken in the integration kernels. The purpose of this paper is to investigate the properties of wave distribution functions reconstructed for wave sources whose central polarization is somewhat deviated from right-handed circular and to study (1) the WDF's by using the right-handed circular polarization in the kernels, (2) the effect of larger deviations for the polarization of elementary plane waves consituting the wave source, (3) the WDF's based on the elliptical polarization kernels and (4) the effect of limiting the number of eigenvalues. It is then found that changing the polarization model in the integration kernels would be helpful in finding out the polarization of the actually observed signals.