Real time on-the-fly kinematic GPS
Considerable interest has been show in the development and application of real time On-The-Fly (OTF) kinematic GPS. A major error source and limitation of such a positioning technique is that caused by cycle slips. When these occur, the integer ambiguities must be resolved for, which can take hundreds of epochs to complete depending on satellite availability and geometry. This research has focused on investigating the applications of real time OTF GPS, as well as its limitations and precision, which has been shown in the thesis to be precise to a few millimetres. The limitations of such a system at present include the use of UHF telemetry links, which at best have a line of sight range of -10 km. The research has shown that alternatives are required, and the use of a relay station can prove invaluable. Cycle slips are another major limiting factor when using OTF GPS, as once a cycle slip occurs, it can either be corrected for or the integer ambiguities resolved for. The second option can take hundreds of seconds, depending on the algorithms used and the satellite number and geometry. This research has partly focused on the development of software which will instantaneously detect and correct for cycle slips in high rate GPS data. The applications of real time OTF GPS are numerous. Research has been carried out to investigate its use to monitor and control construction plant as well as monitoring the movement of large structures. As OTF positioning is precise to a few millimetres, it is ideal for the control of construction plant, and has been compared to laser levelling and precise digital levelling. Such a GPS system gives the user a 3-dimensional position for the bulldozer blade, for example. Such information can prove invaluable for quality control as well as developing an automated system, which would be controlled by real time OTF GPS. In addition, real time OTF GPS has been shown in the research to provide instantaneous positioning of large structures in the form of bridges. Such information could provide future systems which would monitor the structure for dangerous movements, resulting in a failure alarm. Carrier phase kinematic GPS has previously been shown to work over baseline lengths of < 20 km. The use of Multiple Reference Stations (MRS) has been shown in this research to enable OTF GPS to be applied over longer baseline lengths, with a precision in the order of 12 cm over 132 km.