EGNOS improved accuracy allows precision farming

Precision farming is the use of various techniques to make the cultivation of agricultural land more efficient, thus enabling farmers to make substantial savings. However, the cost of the equipment needed for precision farming remains high, which restricts its use to large farms. This is mainly due to the fact that equipment manufacturers offer solutions using real-time kinematic (RTK) or differential Global Positioning System (DGPS) techniques. Now, EGNOS is able to give farmers on small- and medium-sized farms access to high-performance equipment at low cost.

Advantages of EGNOS

The two key parameters for precision farming are:

  • accuracy of positioning to help with guidance of agricultural vehicles;
  • accuracy of positioning from one pass to the next and from one year to the next for the agricultural vehicle;
  • revisit capability.

EGNOS appears particularly well-suited to this type of application, as it considerably improves positioning accuracy compared to when GPS is used by itself. In addition, the services offered by EGNOS are affordable, requiring only the use of a single-frequency receiver, which costs much less than RTK positioning systems.

Architecture

The diagram below shows the architecture of a simplified guidance system for an agricultural vehicle. This system consists of an offset antenna placed on the vehicle’s roof, a GPS/EGNOS receiver and a computer running the guidance application. As an option, the receiver can be connected to an odometer, which improves guidance accuracy.

Figure: Architecture of the guidance system for an agricultural  vehicle

Figure: Architecture of the guidance system for an agricultural vehicle

All the differential corrections broadcast by EGNOS are used for this application, including fast corrections, long-term corrections and ionospheric corrections.

There are no particular constraints with the receiver. Any EGNOS-compatible model that can calculate all the differential corrections is suitable. The offset antenna on the vehicle’s roof offers a better reception of the GPS and EGNOS signals.

Implementation

Using the EGNOS service is relatively simple with this kind of application. The differential corrections broadcast by EGNOS are taken into account directly by the receiver. The receiver is generally connected to the computer running the guidance application via a serial link. When the guidance application starts up, it is however necessary to:

  • send the receiver the configuration parameters telling it to use EGNOS,
  • if necessary, exclude the satellite used for EGNOS testing,
  • if necessary, force the use of EGNOS despite the broadcasting of an MT0/2 type message.

 

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