Phase center variations problem in GPS/GLONASS observations processing

It is generally known that the phase center of a GNSS antenna is not a stable point. For any given GNSS antenna, the phase centers will change with the changing direction of the signal from a satellite. The problem is particularly important when different antennae are used in measurements. Ignoring these phase center variations in measurements can lead to serious vertical errors. The way to avoid these errors is by applying antenna phase center variation models in processing. Three major methods are presently available to determine mean antenna phase center offsets as well as variations of the phase center with elevation and azimuth for GNSS receiver antennas. Because of this and because of some problems in introducing of absolute models at present we can speak of three models of receiver antennas PCV (relative, absolute converted and absolute) and two of satellites antennas (standard and absolute). Additionally, processing simultaneously observations from different positioning systems e.g. GPS and GLONASS, we can expect a further complication resulting from different structure of signals and differences in satellites constellations. The aim of this paper is to study the height differences in short static GPS/GLONASS observations processing when different calibration models are used. The analysis was done using 24 hour GNSS data divided by one hour observation sessions. The results show that switching between different PCV models may have a visible effect on height determination, particularly in high accuracy applications.