How the EU satellite positioning system will benefit farmers
Many arable farmers are benefiting from navigation technology using satellites to steer their tractors and sprayers across fields with pinpoint accuracy to save on sprays and fertiliser by eliminating costly overlaps.
Technology is also used by combines to generate yield maps, as well as allow farmers to record the position of weed patches in a field using their smart phone.
And from the middle of 2017, farmers will be able to use the European system, which promises better coverage and accuracy.
– Europe – Galileo
– Russia – GLObal NAvigation Satellite System (GLONASS)
– USA – Global Positioning System (GPS)
– China – The BeiDou Navigation Satellite System (BDS)
– India – Indian Regional Navigation Satellite System (IRNSS)
Up to now, European farmers have been managing with the US GPS and Russian GLONASS, both of which are freely available. The Chinese also have a system, but this is currently accessible only in China and other parts of Asia and Australia. Also in Asia, India is working on IRNSS.
So to make Europe less dependent on the Russians and US, the EU embarked on the Galileo project. The Galileo system came online on 15 December 2016 and farmers should be able to use it in the second half of 2017.
Initially it will be a limited service – as only 18 out of the planned 30 satellites are in orbit – before being fully up and running 3 years later. The other aim of the project, which is of more interest to farmers, is that it increases the number of available satellites, which makes location finding easier.
Shadow from trees and tall buildings means that there are sometimes fewer satellites with a good line of sight to the receiver than the minimum of 5 theoretically required for real-time kinematics (RTK), but in practice many more satellites are used.
Shadow is not much of a problem for farmers, though Galileo may improve reception in built up areas where receivers are surrounded by tall buildings. Therefore, navigation systems such as TomTom will undoubtedly be more accurate if they use Galileo.
Galileo claims it will soon have the best worldwide coverage, though GLONASS offers better cover at the poles because its satellite orbits have a higher angle of inclination. Plans for Galileo’s commercial services include transmitting a correction signal for its satellites, which should provide centimetre precision, though even 10cm is regarded as accurate.
Europe also has the advantage of building on existing experience and technology. The US began developing GPS in 1967, but Europe did not follow suit until some 30 years later and is, therefore, in a position to apply the very latest technologies.
Receivers are Galileo ready
Over the past 3 to 4 years, all machinery suppliers have upgraded their receivers to handle signals from Galileo. In the Netherlands, mobile internet-based networks such as Agrospin and MoveRTK are still working on software updates, and MoveRTK’s Jean-Paul Henry says his company is liaising with various suppliers.
Customers with Galileo-ready receivers should be able to use them in the second half of this year. In terms of technology platforms, GPS’s L1 and L5 frequencies are the same as Galileo’s E1 and E5a, making it easy to combine the 2 systems in receivers.
Not all going to plan
But the EU project hasn’t been glitch free. The European Space Agency (ESA) claims that Galileo will be fully available in 2020, although this date has already been postponed several times with only 5 of the first 18 satellites in operation.
Nine clocks on 5 Galileo satellites are not working, and while new launches are planned, the ESA is currently deciding whether to work out why the clocks are failing before continuing with these. Paul Verhoef, head of ESA’s satellite navigation directorate, does not believe this will actually put the 2020 deadline at risk.
However, further evidence that theory often has little to do with reality can be seen with the budget. The project’s initial budget of €3bn ($3.17bn) has now increased to €10bn ($10.17).
How GPS positioning systems work
Ultra-high-precision atomic clocks mounted on satellites orbiting some 22,000km (13,670 miles) above the Earth transmit radio signals at the speed of light, some 300,000km (186,411 miles) a second.
The electronic antenna in the receiver calculates how long these have taken to arrive, and thus how far they have travelled. Time differences are measured in minute fractions of a second.
Therefore, the more accurate those satellite signals can be, the more accurate geolocation can become. Geolocation also becomes more precise when more satellites are used, since time differences can be averaged out.
The simplest form of GPS has a variance of a few metres. Differential GPS uses a signal from a fixed station whose exact location is known, giving a maximum accuracy of 30cm (12in).
And RTK technology compensates for satellite movements to achieve an even greater precision of around two centimetres by transmitting a correction signal from a base station.
Some companies have their own RTK stations, and other commercial networks share them on a subscription basis.