Real-Time Kinematic (RTK) positioning strengthens the precision of GNSS data. GNSS signals from satellite constellations including GPS, GLONASS, Galileo and BeiDou can be subject to errors. RTK utilises additional GNSS carrier wave measurements to minimise errors and so determine a truer accuracy of the distance between the receiver and the satellite.
RTK positioning works by correcting GNSS errors such as:
- satellite clock drift
- ionospheric and tropospheric delay
- orbit variation
- multipath propagation
RTK UAVs equipped with RTK receivers can collate data broadcast by RTK base stations. A Continuously Operating Reference Station (CORS) network of real-time kinematic base stations can increase the accuracy of GNSS data. Using multiple base stations reduces redundancy time and any errors occurring within data streamed from any one base station, and so enhances reliability still further.
Typically broadcasting using UHF radio, there is a limit to the range UAVs can receive signal from a single base station. The use of a CORS network of base stations therefore extends the usable range of flight.
Multiple unmanned vehicles can receive position corrections broadcast by a single RTK base station. As well as unmanned aerial vehicles; drones, UAVs and UAS, real-time kinematic positioning is also utilised on land by unmanned ground vehicles (UGVs) and at sea by autonomous surface vehicles (ASV), unmanned surface vessels (USV) and numerous other robotic platforms including autonomous parking and driving systems and unmanned tractors.
Unmanned vehicles equipped with RTK technology are often used for mapping and surveying. This is because it’s capable of improving the precision of GNSS receivers from several metres down to centimetre-level. Crucially this is done in real time, enabling images to be more accurately and immediately geotagged. The installation and position measurement of GCPs can be an arduous task within drone mapping and so the ability to reduce the requirement for GCPs (ground control points) is another reason aerial mappers and surveyors favour real-time kinematic drones.