Calibration of antenna-radome and monument-multipath effect of GEONET - Part 1: Measurement of phase characteristics

Severe, 10-cm level, elevation angle cutoff dependence of the height solution is detected in the analysis of sample baselines from GSI/GEONET (Geographical Survey Institute/GPS Earth Observation NETwork). It is inferred that station and monument specific differences in the radome and/or multipath environment are responsible for this effect, because it can be observed over short sample baselines for identical antennas mounted atop different monument types. Our test results show that both the radome and multipath from the metal plate at the top of the pillar affect the baseline solutions. A calibration experiment was carried out by observing short (<10 m) known baselines to obtain phase correction maps for the typical GEONET monuments. The antenna/monument phase centers of GEONET monument replicas with the same attachment and radomes but shortened in height, were determined relative to a tripod-mounted TRM29659.00 antenna. Phase maps were obtained with the BERNESE software for 6 typical combinations of 3 antenna types, 3 monument types, and 3 radome types commonly used in GEONET. We find monument/antenna specific phase differences up to 1 cm. These phase differences can result in more than 10-cm station height biases when tropospheric delay parameters are estimated, which is consistent with the height errors observed for GEONET.