Method of remote sensing of horizontal stratification due to an ionospherically reflected powerful radio wave

Abstract

It is shown numerically that the group delay of a weak diagnostic radio wave is greatly reduced in the presence of a powerful radio wave of slightly lower frequency vertically incident on the ionosphere below the penetration frequency. The numerical results are qualitatively interpreted in terms of a narrow stop band for propagation in a spatially periodic medium, for wavelengths near twice the spatial period. Application to remote sensing of the horizontal density stratification in ionospheric modification experiments is discussed.

Artificial periodic irregularities in the auroral ionosphere

“…Lapin and Tamoikin (1984) showed that the curvature of the periodic structure affects the probe-wave scattering only slightly if the distance between the height of the probe-wave scattering and pump reflection height is small compared with their distance from the receiver. These authors also concluded, in what appears to be work closely related to that of Fejer (1983), that the effect of a periodic lattice on the wave reflected from the F region can lead to attenuation. Lapin (1994) looked at the combined effects of ambipolar diffusion and turbulence on the relaxation time of the scattered waves from the E and D regions.…”

“…There was a region of backscatter extending 10 km or more below the specular reflection height immediately after heater switch-off and which decayed, apparently moving upwards to the specular reflection level within about 100 ms. Perhaps this was an electron-density stratification in the Airy pattern of the standing HF wave which decayed. The large extent of more than 10 km below the reflection height may have been only an apparent one if the reduction in group delay for frequencies just slightly off the pump frequency really occurs as predicted by Fejer (1983). Although the probing wave was at the same frequency as the pump wave, the 60-s pulse length ensures that there is significant energy within a several-kHz bandwidth.…”

“…For the F-region horizontal stratification, Fejer (1983) predicted a large decrease in group delay for weak diagnostic waves just below the frequency of the powerful modifying wave and an increase in delay for frequencies above the modifier, which could be a new diagnostic technique for detecting the degree of density change. So far this idea seems not to have been tested.…”

Measurements of artificial periodic inhomogeneities at HIPAS Observatory

“…Finally, we note that Fejer [1983] suggests a powerful diagnostic approach that could be used to measure absolute electron density perturbations associated with F region API. Because API gives rise to a spatially periodic medium, there is a substantial reduction in the group delay of probe waves having frequencies slightly greater than the modifying wave.…”