How do DGPS and RTK systems differ in their correction signal source and achievable accuracy?

DGPS (Differential GPS) and RTK (Real-Time Kinematic) are both GPS augmentation systems used to improve the accuracy of GPS positioning, but they differ in their correction signal source and achievable accuracy. DGPS utilizes correction data from a network of ground-based reference stations. These reference stations know their precise location and calculate the errors in the GPS signals they receive. They then transmit these correction signals to GPS receivers in the field. The correction signals can be transmitted via radio beacons, satellite links, or internet connections. DGPS typically achieves accuracy in the range of 1-3 meters. RTK, on the other hand, also utilizes a reference station, but it requires a more sophisticated setup. The RTK reference station transmits raw GPS data, including carrier phase measurements, to the RTK receiver in the field. The RTK receiver then processes this data in real-time to calculate a highly accurate position. RTK typically achieves accuracy in the range of 2-4 centimeters, significantly more precise than DGPS. The key difference lies in the use of carrier phase measurements. Carrier phase measurements are much more precise than the code-based measurements used by standard GPS receivers. However, RTK requires a strong and stable communication link between the reference station and the rover, as well as more complex processing algorithms. For example, in precision agriculture, DGPS might be used for tasks such as soil sampling or mapping, where meter-level accuracy is sufficient. RTK would be used for tasks such as autosteering and variable rate application, where centimeter-level accuracy is required.