Drift-parallax determination of the altitude of traveling ionospheric disturbances observed with the Los Alamos radio-beacon interferometer

From 1993 to 1997, the Los Alamos very long baseline interferometer was rou tinely employed to detect traveling ionospheric disturbances (TID) and inne r plasmaspheric irregularities by measuring the change in the electrical ph ase of several satellite beacon signals that backlit the inner plasmasphere and ionosphere from geosynchronous orbit. The fortuitous placement of two satellite beacons nearly in the Los Alamos geographic meridian, in late 199 5, permits us to infer the nominal altitude of each TID event by employing a novel parallax ranging technique. In the context of this paper, the nomin al altitude of a TID refers to the altitude at which the slant-path average d, amplitude-weighted phase perturbation existed along the lines of sight f rom the interferometer to the satellite. In this paper, we outline the meth od and present validation results.