Precision Ag Blog

Nov 18
Explanation of GPS/GNSS Drift

The Alabama Precsion Ag team has developed a visual aid to illustrate GPS/GNSS drift. The display is a “to scale” model that allows producers to grasp the impact GPS/GNSS drift can have on an agricultural operation. If you have dropped by the Alabama Precision Ag team’s booth at a conference or field day this year, you have probably had an opportunity to see the display. We have received many inquiries about the display and requests for additional information. There is a new Timely Information sheet on this topic posted on our website, Explanation of GPS/GNSS Drift. Hopefully this blog and Timely Information sheet will answer questions you may have concerning the display or GPS/GNSS drift. If not, please contact a team member for additional information. Below is a description of each part of the display as well as its significance. 

Banner: The first paragraph of the banner references a scenario of a producer harvesting peanuts. His tractor is off the target path and the error is attributed to GPS/GNSS drift. Definitions of GPS/GNSS drift and pass-to-pass accuracy allow the spectator to understand why the manufacturer’s advertised accuracy (typically pass-to-pass) may not be experienced in the field. Next, solutions to GPS/GNSS drift are given with upgrading to a lower drift correction (SF 2 or OmniSTAR), or ultimately RTK, recommended. The table illustrated in the banner quantifies pass-to-pass accuracy and drift ranges for four correction services according to Auburn University research. Finally, the last paragraph gives insight into the importance of choosing the appropriate correction service for a particular operation.clip_image003

Carpet: At the top of the banner, there is a tractor moving across a field. Behind the tractor are four differently colored intervals that come toward the spectator and out of the banner onto the carpet. These colored intervals are “to scale” representations of GPS/GNSS drift or year-to-year accuracy of four correction services. Blue represents WAAS, red represents a sub-meter service, yellow represents a decimeter level service, and green represents RTK level correction. It is evident in figure 1 (left) what a substantial impact GPS/GNSS drift can potentially have on field utilization efficiency. Note: these cotton rows are planted on 40 inch centers. Standing on this carpet, the spectator can truly appreciate the year-to-year accuracies of these correction services. See figure 2 (below) for a schematic of the full display.

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Written by Daniel Mullenix, Research Engineer, Biosystems Engineering, Auburn University.


























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