The GPS antenna fitted to the machine receives continuous signals from the GPS satellite constellation. Ground based GPS receivers, at known locations across Europe, receive the same signals. As their absolute location is known, they can calculate the real time position error, and via uplink stations, send a position correction message to geostationary satellites.
These geostationary satellites then beam down the correction message to the GPS receiver on the vehicle, and the correction can be applied to the received position.
The U.S. GPS (Global Positioning System) satellite network determines the position of a vehicle using signals from 32 satellites that circle the earth every 12 hours. These satellites travel at about 20,000 kilometres above the earth in known orbits that allow a land based receiver to determine its own position in relation to each satellite from which it receives a signal. An extremely precise atomic clock on board of each satellite is used to program the transmission of GPS signals at regular intervals.
The Russian navigation satellite network GLONASS uses the same principle as the GPS network emitting signals at different frequencies. Some agricultural applications require a level of precision that can only be guaranteed by the joint reception of signals from both the GPS and GLONASS networks, in order to ensure adequate satellite coverage and the required correction.
To provide this capability, some of our receivers are able to process GPS and GLONASS satellite signals, offering users a higher level of “productivity
insurance” than the single constellation receivers.
To give you the precision you need, New Holland PLM offers four levels of accuracy, down to 2.5 cm
An uncorrected GPS or GLONASS signal gives you position accuracy between 5 to 10 meters. This is more than adequate for car navigation systems, but not accurate enough for vehicle guidance in agricultural applications, where we need Pass to Pass and Year to Year accuracy and repeatability.
Pass-to-Pass accuracy measures the relative accuracy over a 15 minute interval. This is usually thought of as skip/overlap from one pass to the next when driving swaths. A New Holland receiver with pass-to-pass accuracy of +/- 2.5 cm means you get less than 2.5 cm skip or overlap, 95% of the time.
Year-to-Year accuracy is the measure of repeatable accuracy which means that you can drive the same rows a day, week, month, or year later. So, +/- 2.5 cm year-to-year accuracy means you can drive the same rows next year within 2.5 cm of this year’s rows, 95% of the time.