ABSOLUTE IONOSPHERIC VERTICAL ELECTRON-CO NTENT INFERRED FROM TRANSMISSIONS OF THE GLOBAL POSITIONING SYSTEM

The signals transmitted at 1,575.42 and 1,227.6 MHz by the GPS satelli tes are dispersively retarded by propagation through the ionosphere. U sing the phase delay and group delay (pseudorange) recorded at both fr equencies by GPS receivers, we construct an observable to measure the total electron content in the ionosphere. After correction for a recei ver-generated offset between the two group delays, this observable yie lds the diurnal variation of the vertical electron content above the r eceiver. Comparisons with a standard model and with data obtained from the European Incoherent Scatter (EISCAT) VHF radar indicate that the technique is accurate in mid-latitude regions.