Guidance and Steering Systems in Precision Agriculture
Types of GPS Receivers
Standard GPS signals are free to broadcast to all users, but the accuracy of these signals alone is limited. The GPS signal must be combined with a correction or augmentation signal to improve the system’s accuracy to levels acceptable for guidance. The type of receiver the guidance system uses determines the correction or augmentation signal received and how these signals are processed to improve accuracy. These correction signals can be divided into three general categories: public augmentation services, subscription augmentation services, and real-time kinematic (RTK) systems. Costs increase with position accuracy. Selecting a correction signal that will meet the operational needs may be desired without going beyond what is required. The type of receiver needed for your operation will depend on the intended use. Table 13.3 presents many common field operations that each type of receiver is capable of handling. Use this table as a guideline to select the minimum kind of receiver technology needed when choosing a specific brand and model. When talking with the preferred precision agricultural equipment dealer, account for overall cost, features, ease of use, mobility, and upgradability.
Public Augmentation Systems
A public augmentation system refers to a GPS receiver that utilizes a publicly available augmentation system to significantly improve the accuracy of its positioning data by receiving correction signals broadcast from ground stations, enhancing its reliability and precision beyond standard GPS alone; essentially, it allows for more accurate location information by incorporating additional data from a network of reference stations.
Subscription Augmentation Services
Subscription augmentation systems (SAS) GPS receivers use a subscription-based service to enhance their accuracy, reliability, and performance. These systems typically augment the standard Global Navigation Satellite System (GNSS) signals by providing additional correction data through ground stations, satellites, or internet connections. In principle, greater locational accuracy allows for more efficient field operations and the potential to lower operational costs of production associated with seeding, tilling, and nutrient application by reducing overlaps and skips in the field.
Real-Time Kinematic (RTK) Systems
Real-time kinematic GPS is a type of GPS technology that uses a combination of GPS signals and a local base station to provide highly accurate positioning data. Unlike traditional GPS systems, which rely on data from satellites alone, RTK GPS systems use additional data from a nearby base station to improve the accuracy of the GPS data. This can provide positioning data that is accurate to within centimeters, making it ideal for a wide range of applications in agriculture. The basic principle behind RTK GPS is simple: by using a local base station in addition to satellite signals, the system can correct any errors that may be present in the GPS data.
RTK Service Providers in Agriculture
In the agricultural field, several RTK service providers offer precision guidance systems and RTK corrections for enhanced accuracy in farming operations. Some of the most common include RTK networks like those offered by John Deere and Trimble, as well as individual providers like Ag Leader and Topcon Positioning Systems. These systems utilize RTK technology to achieve centimeter-level accuracy, improving efficiency and minimizing errors in tasks like planting, spraying, and harvesting (Table 13.5).
WAAS Versus SAS Versus RTK Systems
As mentioned, WAAS, SAS, and RTK systems are methods for enhancing the accuracy of standard GPS/GNSS receivers. However, they differ significantly in their underlying technology, operational requirements, and applications.
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