RF Interference and Multipath Effects at Continuous GPS Installations for Long-Term Monitoring of Tide Gauges in UK Harbours

Large numbers of continuous GPS (CGPS) stations have been established in port or harbour environments, either as reference stations for differential GPS (DGPS) operations or for scientific research into climate related global sea level changes. Although the error budget for these applications is quite different, i.e. at the centimetre level for DGPS and the millimetre level for scientific use, reduced data quality of CGPS measurements due to possible radio frequency interference (RFI) or increased amounts of multipath is intolerable. Data from two scientific CGPS stations established in order to monitor 3- dimensional land movements at tide gauges situated in UK ports have been investigated. One site was affected by RFI, compromising the tracking capability for signals of satellites in elevations of 25 to 40o, across the horizon. The second site is affected by large multipath and signal obstructions. On several geodetic receivers the effects of the apparent RFI have been investigated. Using a spectrum analyzer and a wide-bandpass Horn antenna the RF interference source was identified. TEQC was then used to investigate the RF interference and pseudo range multipath at both CGPS stations.