Accounting for ionospheric variability and irregularity in high frequency direction finding

The general properties of ionospheric irregularities and the order of magnitude of the errors introduced into position location accuracies are outlined. The spatial and temporal coherence of the ionospheric irregularities are estimated, while addressing the usefulness of a single ionospheric sounding as opposed to multiple and spatially separated soundings. It is found that ionospheric data (tilt and virtual height of reflection) taken at one point, lose validity when extrapolated over distances of 50-100 km, or over times of more than five minutes. It is concluded that a single ionosound is usually not sufficient to adequately represent a large enough area of the ionosphere, and thus an integrated network of ionosounds, using vertical and oblique sounds is recommended.