From 1993 to 1997, the Los Alamos very long baseline interferometer was routinely employed to detect traveling ionospheric disturbances (TID) and inner plasmaspheric irregularities by measuring the change in the electrical phase 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 1995, 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 nominal altitude of a TID refers to the altitude at which the slant-path averaged, amplitude-weighted phase perturbation existed along the lines of sight from the interferometer to the satellite. In this paper, we outline the method and present validation results. ¿ 1998 American Geophysical Union