What is RTK and why does it matter
By Steve Fairchild
MFA Precision Advantage is building a network of real-time kinematics towers to provide better accuracy and more applications for precision farming.
Real Time Kinematics is a radio-based correctional signal that provides Global Positioning System with horizontal and vertical accuracy. For a farmer inside of MFA’s RTK network, that means the GPS receiver with RTK can provide sub-inch accuracy day-to-day and year-to-year for anhydrous, strip-till, tillage, planting, spraying and harvesting. It’s another layer of usefulness for all the electronic geegaws that have found a bracketed home in your tractor these days.
And, in the case of RTK, the usefulness comes in the form of accuracy. Accuracy—the point of “precision” farming—brings increased efficiency to row croppers. Operators burn less fuel, have less chemical overlap, fewer planting gaps, etc. Paired with auto steering systems, GPS/RTK reduces operator fatigue. And, with the year-to-year repeatability that RTK brings, you can forget about troublesome row markers on the planter, or you can employ a controlled traffic plan.
“The important thing about RTK is that you get accuracy down to 1-inch and you get it day after day, month after month and year after year,” said Rick Greene, MFA Precision Agriculture manager.
Greene explained that the GPS signal accuracy broadcasted by 31 active satellites positioned around the globe is always affected by autonomous error, time, atmosphere and space conditions. This satellite constellation shifts relative to the earth’s surface causing what the industry calls “GPS drift.” The only way to correct for these errors is through a fixed GPS correctional signal like RTK.
For applications such as documenting where you are when you take a soil sample or staking out a field boundary, several inches of variation doesn’t much affect the results. These are one-time or at least infrequent tasks. But when it comes to running a tractor on GPS-based automatic steering, a few inches drift multiplied by the number of passes it takes to raise a crop can be of significant impact to time and input costs.
“Some people believe that a producer has to farm many acres to make this type of technology pay,” said Greene. “I think a bit differently. A 4,000-acre producer who travels over his fields three times covers just as many acres as a 2,000-acre producer who travels over his fields 6 times a year. The auto steering system doesn’t care about the farm size, it saves based on the number of passes and cost of inputs it takes to raise a crop. If you have a 30-foot implement and overlap approximately 3 feet, which isn’t uncommon, you’re 10 percent less efficient than you could be with fuel, products, and time. In theory, a producer with 1,000 acres with 10 percent greater efficiency could farm 100 more acres. So technology like this has a return on investment regardless of farm size.”
Real-time kinematics is a hefty term that basically means a land-based correctional signal is employed to augment satellite signals received at the vehicle.
A tower equipped with its own GPS receiver communicates with the vehicle’s GPS receiver to correct positioning down to vertical and horizontal sub-inch accuracy. Both receivers use the richer L2 Band signal for increased accuracy. Such accuracy is repeatable because the base stations, in this case towers operated by MFA, are permanently fixed in the same spot on the earth.
To make it work, you need a GPS receiver, radio receiver, terrain compensator and the hydraulic controller that is plumbed into the tractor’s steering hydraulics for automatic steering.
“Cost to get an RTK setup varies according to components supplier pricing, but figures range from $15,000 to $25,000 dollars. “If a producer farms 1,000 acres, makes 5 trips across the operations and utilizes the auto steer for 4 year, his auto steer system will cost only $1 per acre.” Said Greene
An RTK setup also provides accurate elevation data.
“Accurate elevation data is something that a lot of producers have not incorporated into their management strategies because the technology hasn’t been readily available to the general farm-level GPS user. RTK elevation can be used for plotting drainage patterns or land-grading fields to eliminate ponding pockets.
You can also use this data to work with NRCS projects such as tiling, waterways or terrace strategies. The best thing about grading with RTK elevation is that you are not dealing with the time constraints of surveying or limitations of laser leveling systems,” said Greene.
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