Tech Chat | What are the sources of RTK errors and how to avoid them?
For the application of GNSS positioning and navigation technology, such as surveying, machine control, precision agriculture, etc., RTK technology is most commonly used. So what are the main sources of RTK error? How should we avoid these errors in daily use so as to obtain more accurate positioning?
When the GNSS signal passes through the ionosphere, the path of the signal will bend, and the propagation speed will also change. At this time, the distance obtained by multiplying the propagation time of the signal by the speed of light in vacuum is not equal to the geometric distance between the satellite and the receiver. This deviation is called ionospheric refraction error.
Solution: RTK technology uses differential data sent from the base station to substantially correct system errors such as ionospheric errors for rovers. For this kind of RTK error, we can select a powerful GNSS RTK receiver to guarantee the RTK accuracy.
Baseline Distance Error
Most high-precision RTK receivers claim an accuracy of 8mm+1ppm. The ppm here means that the distance between the rover and the base increases by 1km, and the RTK error will increase by 1mm. So this is the error caused by the increase of the baseline distance.
Solution: This error is an objective error of the RTK method. In daily work, it’s better to keep the distance between the rover and the base station within 20km to ensure the surveying accuracy.
Multipath interference occurs when the satellite signal is reflected off a surface, such as a building or a vehicle, and arrives at the RTK receiver at different times, causing errors in the GNSS measurements.
Solution: During the measurement, try to avoid large reflective surfaces, such as water surfaces, glass buildings, etc. For some monitoring or CORS projects, users can also use choke ring antenna to eliminate multipath errors.
Satellite Signal Quality Error
Poor satellite signal quality will also lead to large RTK errors. This is usually caused by severe occlusion or signal interference in the environment, such as dense forests, buildings, electric towers, etc.,
Solution: For the base station, it's best to set up under an open sky view. For rover, surveyors can select full-constellation RTK receivers, which can track more satellites even in harsh environments.
In daily surveying, errors may also occur due to improper human operation, such as the point is not aimed, the pole is not centered, and so on.
Solution: For human error, it can only be avoided by the care and experience of the surveyor. However, surveyors can also choose an RTK receiver with an IMU, which can measure without centering the pole, reducing fatigue and errors.
With the rapid development of the GNSS industry today, the powerful performance of the equipment has greatly eliminated various common errors. Therefore, choosing an advanced and reliable RTK device is the best way to get accurate results.
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