What is RTK GPS?
Real-Time Kinematic (RTK) is a technique used to reduce and remove common positioning errors. Rather than use code-based positioning, RTK GPS uses carrier-based ranging and provides real-time corrections with the help of a single reference station. This enhances the precision of position data received from satellite-based positioning systems, and results in the centimeter-level accuracy required for many applications.
When using code-based positioning, a receiver can establish its position by determining the ranges of at least four satellites. These ranges, along with the known position of the satellite enable the receiver to establish its position within a few meters. On the other hand, carrier-based ranging calculates a position by determining the number of carrier cycles between the satellite and the rover station, and multiplying this number by the carrier wavelength. Carrier-based ranging has the ability to produce more precise measurements.
RTK GPS Segments:
RTK GPS consists of three segments: a base station, one or more rover users, and a communication channel. The base station monitors satellite signals and sends information to the rover user(s) through the communication channel, which allows the base to broadcast correction data in real-time. Satellite measurements are transmitted to receivers from a fixed reference station, the exact location of which is known. By combining their measurements with those of the reference station, these receivers are able to remove common errors such as ionosphere errors and satellite clock errors. Once these errors are removed, the phase measurements can be used to determine an exact position within 2-5 centimeters.
RTK GPS provides highly accurate positioning information, and should ideally be used to establish several unknown points within the vicinity of the known base location, and when it is important that the coordinates be delivered in real-time. For best results, it is recommended that the distance between the rover receivers and the reference station be limited to between 20 and 30 kilometers, after which RTK GPS position accuracy begins to decrease.