Differential GPS (DGPS)

The concept of a differential GPS (DGPS) real-time system is illustrated in Figure 2.

The DGPS system improves the position accuracy by using the differential technique. This is accomplished by accurately surveyed GPS Reference Stations which calculate pseudo range corrections for all the satellites tracked by the Reference Station's GPS receiver.

The DGPS system also utilises a communication link for transmission of correction data from the Reference Station to the Vessel Unit.

Each GPS Reference Station compares the measured distance to a satellite with the one calculated based on the satellites' and the reference station's known co-ordinates. The resultant range difference is the correction data, which is broadcast from the GPS Reference Stations to the Differential GPS correction receiver(s) on board the vessel(s).

Figure 2 Differential GPS (DGPS) Concept

At the vessel, these pseudo range corrections are applied to correct the pseudo ranges received by the vessel's GPS receiver, prior to using them for the calculation of a three-dimensional navigation solution.