The Integration of GPS and Pseudolites for Bridge Monitoring

One application in structural engineering is measuring the movement of suspension bridges. Under unfavourable wind conditions or heavy traffic loads cable suspension bridges may move up to a few metres. Therefore, a positioning system used to monitor bridge movements can provide extremely valuable information. For such monitoring applications it is desirable for the positioning system to deliver equal precision in all position components, all the time.GPS has the potential to deliver cm-level positioning accuracy, through use of the very precise carrier-phase measurement. However, the same level of accuracy cannot be guaranteed in all three-position components, twenty-four hours a day, in every situation.Additionally, GPS signals are very weak and easily obstructed, especially in built-up urban environments. One solution to improving the GPS satellite geometry and the availability of ranging signals is to use ground-based transmitters of GPS-like signals (called “pseudolites”). A major advantage of pseudolite devices is the ability to control where they are located, improving a geometrically poor GPS constellation.In this paper proof of concept for the use of pseudolites in the monitoring of suspension bridges is demonstrated through an experimental trial conducted on the Parsley Bay suspension footbridge in Sydney, Australia.