How are the National GPS Network Active stations monitored?
A. The positional quality of every Active Network station is monitored constantly in real time by the OS Net software. The real time computed coordinates are constantly compared with the station’s accepted ETRS89 coordinates (which are based on at least 2 weeks data) and the differences in East, North and Up directions are computed. These differences can be displayed as a graph to give an indication of the “positional noise” of a station. An example graph is given below for station SCAR. Alarm thresholds are set in the software so that if a station’s real time coordinates significantly differ from the accepted coordinates an alarm message is sent to the software operators. In this case the station would be immediately removed from the network and the reason for the movement investigated.
