An evaluation of systematic errors in VLF direction findings via full‐wave analysis

Abstract

The full‐wave analysis method is described for computing the electromagnetic field on the ground when a beam‐shaped wave is incident from above the ionosphere. By means of this method, the directional error was evaluated in various VLF direction finders which measure the exit point of the natural wave at the lower portion of the ionosphere, under the assumption that the downgoing wave is radiated from a duct. In this method, the directional errors due to multiple reflection, polarization, beam wave of the arriving radio wave and the type of ionospheric models can be found systematically so that a simulation result most resembling the practical situation is provided. The main results are as follows: (1) When the transmission cone is within the trapping cone, the NPF method using orthogonal loop antennas and vertical antennas can indicate an almost correct direction within a radius of about 100 km from the maximum point of the radiowave strength on the ground. The error increases at a distance of more than 150 km. On the other hand, the Poynting method indicates almost correct directions even at a distance of more than 200 km regardless of the polarization. The goniometer method has almost the same accuracy as the Poynting method; (2) if the overlapping of the transmission cone and the trapping cone is smaller, the error is increased in the south direction in all three methods; and (3) no significant frequency dependence is observed in the directional error.

Very low latitude whistlers and the effect of earth‐ionosphere waveguide propagation

“…It is possible to estimate that the whistler transmitted downward through the ionosphere above Zhanjiang with a right-handed circular polarization [ 101 changes to an elliptical polarization during the propagation over a long distance [18]. Po 1 a r i za t i on Parameter Fig.…”

Ray‐tracing studies of the arrival direction and the ionospheric penetration of whistlers at low latitudes

“…Errors appearing in several direction-finding methods and caused by multipath propagation in the Earth-ionosphere waveguide have been evaluated using models by Strangeways [1980] and Nagano and Mambo [1989]. They found that the effect of multipath propagation can be neglected for propagation distances below 100 km in the case of the NPE method.…”