Real Time Kinematic is a technique used to increase the accuracy of GNSS (GPS, Glonass, Galileo, BeiDou) signals by using a fixed base station which wirelessly sends out corrections to a moving receiver (rover). By using these corrections, the RTK GNSS receiver can fix the position of the antenna to within 1 – 2cm.
The technique involves the measurement of the carrier phase of the satellite signal, which is then subject to some sophisticated statistical methods to align the phase of these signals to eliminate the majority of normal GNSS type errors.
This alignment process goes through three phases, acquisition, ambiguity ‘Float’ mode and ambiguity ‘Fixed’ mode. Accuracies in Float mode are in the region of 0.75 – 0.2m and 0.01 – 0.02m in Fixed mode.
There are multiple ways of receiving RTK corrections:
1. Your own base station:
(this always requires a minimum of 2 GNSS receivers) The base station re-broadcasts the phase of the carrier that it observes, and the mobile units (rovers) compare their own phase measurements with the one received from the base station. There are several ways to transmit a correction signal from base station to the rover. The most popular way to achieve real-time, low-cost signal transmission is to use a radio modem, typically in the UHF Band. In most countries, certain frequencies are allocated specifically for RTK purposes. Most land-survey equipment has a built-in UHF-band radio modem as a standard option.
Here are some examples of Rover and Base sets
2. RTK Correction services
(Faster setup and only 1 receiver is needed) The RTK networks extend the use of RTK to a larger area containing a network of reference stations. Operational reliability and accuracy depend on the density and capabilities of the reference-station network. As most countries have their own local network, there are now providers that are capable of covering whole continents. Allowing you to just use one subscription wherever you go.