Apparent diurnal effects in the global positioning system

Significant evidence is found indicating a systematic diurnal variation in the ephemeris and the propagation terms as transmitted from GPS (global positioning system) satellites. It is noted that the proper way to sort these out would be a two-frequency receiver. The presence of a similar diurnal variation even with a two-frequency P-code receiver is also indicated. The significance of using the P-code is that the chip rate of the pseudonoise code is 10 times higher, thus dividing by 10 the effect of multipath variations. It is also shown that a GPS clock can be characterized for periods of less than one day by removing the diurnal variation. It is assumed that the diurnal variation is a systematic error, not a feature of the clock. It is removed by taking only relevant fast Fourier transform values, inversely transforming them, and subtracting them in the time domain. The resultant (GPS-Global UTC(NIST)) data are presented with the Allan variance