What is Differential GPS (DGPS)?

Differential Global Positioning Systems (DGPS) are GPS systems that use fixed reference locations on Earth to calculate positioning errors transmitted by the satellites in view. Since the location of these reference points in already know, they can easily calculate any positioning errors that are being transmitted by the GPS constellation. This error information is then transmitted out to GPS devices, which use this information to calculate their accurate position.

DGPS uses pseudorange corrections and range-rate corrections from the reference station which has enough channels to track all satellites in view. The system calculates the difference between the GPS calculated position for the ground reference station and the actual position of the ground reference station.