Spaced-station observations of travelling ionospheric disturbances - computer simulations and experimental studies

A three-dimensional ray-tracing analysis is employed to calculate ray paths through a model ionosphere which itself is perturbed by the passage of horizontally moving wavelike disturbance. A knowledge of various parameters (e.g. phase and group paths, angle of arrival, Doppler frequency shift) for ray paths connecting a central transmitter with spaced receivers permits an evaluation of several spaced-station techniques for measuring horizontal phase velocities of travelling ionospheric disturbances (TIDs). It is shown that in experiments with transmitter-receiver spacings of less than 150 km, reliable velocity estimates may be expected, even though the assumption of a horizontally stratified ionosphere which is common to all methods is strictly invalid. (author)