| Popis: |
Antenna phase center of GNSS receiver is the point where the signals transmitted from satellites are collected. However, this point is not necessarily the physical center of antenna (geometric center of antenna). In general, for most applications of GNSS, users consider the phase center to be a fixed point. But this point has its variation based on the direction of the radio signal source. Direction of incoming signal from satellite is definite with azimuth and elevation angle. Moreover, antenna phase centre is not only angle dependant, it also depends on the signal frequency. Variation of antenna phase center with the azimuth and elevation angle of incoming signal from satellite and with the frequency of incoming signal is used to called phase center variation. In geodesy (also as well in other areas), there are applications with high accuracy demands in terms of point precision (millimeter accuracy) or some other quantities. For those applications, users must consider the influence of phase center variation. With the appropriate settings, it is possible to estimate the variation of the phase center. The mean phase center and its variation can then be used in the software for GNSS data processing. In this paper, field procedure for estimation of antenna phase center is presented. On stable ground with a clear sky without any obstacles or sources of radiation nearby, a test field has been established. The test field contains two nearby points. Those points have been occupied in four sessions. Based on collected data, mean phase center has been determined, as well as the phase center differences from all four sessions and for each Global Navigation Satellite System independent (NAVSTAR GPS, GLONASS, GALILEO and BAIDOU). In addition, the expanded uncertainty of coordinates has been calculated. |
