|Sudduth, Kenneth - Ken|
Submitted to: Applied Engineering in Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/29/1996
Publication Date: N/A
Interpretive Summary: Precision agriculture, or site specific management (SSM) refers to a strategy in which cropping inputs such as fertilizers are applied at varying rates across a field in response to variations in crop needs. Knowing the accurate location of field operations or data collection points is important in the implementation of these methods. Most current SSM efforts use Global Positioning System (GPS) technology to provide location data. GPS is a satellite-based radio navigation system developed and operated by the U.S. Department of Defense that allows land, sea, and airborne users to determine their three-dimensional position anywhere in the world with a high degree of accuracy. We evaluated the performance of several commercial GPS receivers for application to two common tasks in SSM, location of sample points and mapping of grain yield variations. We found that standard differential GPS equipment and procedures provided position accuracies of 1 meter or better, sufficient for most SSM applications. Higher accuracies could be obtained using more advanced techniques. The impact of this work is that it is one of the first reports of GPS accuracies obtained during actual SSM operations. This information will be useful to researchers and practitioners who need to know the capabilities and limitations of GPS in precision agriculture applications.
Technical Abstract: Global positioning system (GPS) measurement techniques were compared with other independent data sources for sample point location and combine yield mapping operations. Sample point 2dRMS location errors were less than 0.7 meters in northing and easting and less than 1.2 meters in elevation when using C/A code differential GPS (DGPS) processing techniques and data from a high-performance receiver. Higher accuracies were obtained with a kinematic positioning method and the same receiver, but the kinematic method required more time and was less robust. Data from a real-time DGPS receiver was accurate enough to provide combine position information in yield mapping. However, errors in GPS position measurements could introduce as much as 100% error in yield measurements obtained on 1 second intervals. Therefore, distance data from another source, such as a ground speed radar or a shaft speed sensor, was needed to provide sufficient accuracy in the travel distance measurements used to calculate yield on an area basis.