GPS: Where We’re Headed
February 10, 2009 When it comes to precision farming, global positioning is the heart and soul of any strategy a grower might use. Positioning ties all the practices a farmer employs throughout the year to areas, even individual points, on a field.
This power makes it possible for machinery to perform on-the-go tasks in the field, such as variable rate defoliation, but also provides detailed data to help the grower build better, more on-target cropping plans.
As the GPS revolution rolls into its second decade since it truly became a widely available public access technology, much has changed for the better. Satellite signal availability and accuracy options have increased significantly. And over the course of the last seven years, the availability and accessibility of real-time kinematic (RTK) correction has moved rapidly from the new technology on the block to an investment that more and more growers are able to afford.
We’re certainly closer to a vision that Mike Gomes, agriculture product manager for receiver manufacturer Topcon, discussed in a 2006 article in sister publication PrecisionAg Special Reports. “The idea is that global positioning becomes like a utility,” he said. “For instance, when you turn on a light, electricity makes it work; or when you turn on the water, it is clean and usable. Imagine there being no time of day issues, no issues with compatibility or satellites or your position on Earth. It’s just there, always on and ready to use.”
GPS ubiquity is on the move, not just in agriculture but in the market in general. For a modest surcharge, a rental car comes equipped with a GPS locator. Or, you can buy your own for about $100. Inside agriculture, receiver technology has evolved to the point where it is built into most equipment, notes Paul Welbig, marketing manager at Raven Industries.
“The reliability, cost and usability of GPS technology has really reached a point where customers trust it and use it in more and more applications.”
Welbig adds that the ability to shrink the hardware down to a very small footprint has also been important, “because it allows GPS to be integrated into smaller and smaller devices.”
Evolution of the Revolution
GPS has gone through an evolution almost simultaneously with, and arguably no less remarkable than, the internet. Like the internet, GPS was in its infancy back in 1995, and product developers were working on a receiver that provided accuracy good enough for agriculture applications. Initial products were only providing accuracy measured in meters, which didn’t fit the bill, says Sid Siefken, product manager for Trimble.
A little more than a decade later, a grower interested in georeferencing field operations using a GPS system has a wide range of options in receiver technology, from the very basic sub-meter system all the way down to the sub-inch accuracy level. These developments have come both in signal technology and at the receiver level.
There are essentially four sources of GPS signals available today. The Wide Area Augmentation System, built originally to replace the current system for coordinating commercial air traffic, is available at no cost from the federal government. The signal provides accuracy averaging around 6 inches – a bit more or a bit less depending on the receiver used.
OmniSTAR provides a subscription based signal with three options depending on accuracy needs – VBS at the basic level, followed by XP and HP, providing accuracy as good as three inches at the top end. The Coast Guard beacon system also continues to be accessible to growers within range of a beacon.
Finally, there’s real-time kinematic systems, which require a static ground receiver and “rover” receiver that provides true subinch accuracy. The other potential benefit with RTK is repeatability – if the static receiver is returned to the precise same location each time it is used, or is permanently installed in one location, it will provide guidance that is repeatable. That is, you’ll be able to return to the same spot in the field, year over year.
The big news with RTK systems is price point reduction and accessibility. A few years ago, a grower could expect to invest $30,000 at the low end to add RTK. Individual systems come in at under $20,000, and where there are tower networks available to pick up a broadcast signal (for a subscription fee), potentially much less than that.
“For cotton applications, more cost-effective and easy-to-use base stations have put the power of repeatability through use of RTK within the reach of more growers,” says Deane Malott, director of product marketing for AutoFarm.
Satellite Signal Improvements
Many growers have succumbed to the adage “accuracy is addictive,” and climbed aboard the RTK bandwagon. However, satellite-based GPS – and the receivers that use the signal – also have been steadily improving over the years. One of the most significant improvements is the availability of a “dual frequency” signal.
Using a dual-frequency signal, which is built into most RTK systems and is the accuracy difference in OmniSTAR’s HP and XP signals, reduces the effects of interference in the field from things like buildings and trees, and allows the receiver to recover more rapidly from brief losses of signal.
Dual-frequency receivers use two of the GPS frequencies, L1 and L2, explains John Pointon, marketing manager at OmniSTAR. “Up until a few years ago those were exclusively used by surveyors who wanted high accuracy, and because of cost the ag market used only single frequency L1. With L1, you really cannot get better than submeter accuracy.
“People who are serious about automatic steering and planting and strip-till need to be within an inch or two, and thus need a dual frequency receiver,” he continues. “Dual frequency permits better compensation for atmospheric errors and helps with the complex calculations required for high accuracy positioning. This is really where the growth is in the market today.”
Of course, not everyone needs or wants that kind of accuracy. So manufacturers are offering a wide range of accuracy options to meet the price vs. value expectations of growers.
What should you consider when weighing up receiver options? Trimble’s Siefken says you want to pay attention to the antenna design of the receiver. “Our product lineup offers a range of antennas that do different things,” he explains. “We have a patch antenna for the our AgGPS 250 that receives a WAAS correction. We also have the Ag 15 antenna that not only receives WAAS correction, but also the VBS correction from OmniSTAR, so that antenna has a very specific purpose.”
It’s also important to note that newer technology is better. A newer, higher quality antenna will provide the user with a cleaner signal that minimizes “noise.” This is essentially the kind of interference that is generated by reflected signals and obstacles in the path of a signal.
It can be difficult to discern one from another, so understanding the capabilities of various offerings is important. In addition, understanding what it will take to upgrade from a lower accuracy level to a higher accuracy level is important if you expect to move in that direction in the near term.
More Satellites, More Signals
Real-time kinematic (RTK) gets most of the press these days, but satellite-based GPS continues to evolve. Here’s a glance at what’s happening in the sky:
- Upgrades to the North American GPS system will include the addition of two new civilian signal types, L2C and L5. Both are dual frequency signals that will provide more reliability and accuracy than L2. These offerings are at least 5 years off, but on the way.
- From Russia comes GLONASS, a project started by the Soviet Union in the 1970s that is now moving forward with some gusto. The North American-GPS compatible system is not operational as a stand-alone unit. But receivers that feature GLONASS compatibility can utilize the satellites to potentially add accuracy.
- Galileo is Europe’s answer to GPS and GLONASS, but has been very slow to get up and running. Because Galileo is compatible with the current constellation, any satellites that go up will add to the total available to growers, but it could be a decade before Galileo is operational as a stand-alone system.
GET THE NEWSLETTER TODAY!
