GPS Yesterday, Today, and Tomorrow

Global position is arguably the most important tool that precision agriculture practitioners use in their operations. Let’s face it – what good would any of the precision technology be without the foundation of georeferencing that global positioning provides?

And yet, this foundational technology is still evolving as growers and service providers demand better and more consistent accuracy from precision equipment. Where that improvement is coming from and where this will take GPS in the future, should be of great interest to agriculture.

“The idea is that global positioning becomes more like a utility,” says Mike Gomes, agricultural product mnager, Topcon Sauer Danfoss. “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 to use satellites or to understand your position on Earth – it’s just there, always on and ready to use. This is where the technology is headed, and that makes the future look very exciting for the positioning business.”

It will be some time yet before agriculture gets to that point, but it is that level of reliability and convenience that signal providers and receiver manufacturers are striving to bring to precision practitioners.

Rise Of RTK

Global positioning in agriculture today is a relatively mixed bag of technologies and options delivering a wide range of accuracy and reliability. The last couple of years, the industry has seen the rise of real-time kinematic (RTK) systems, driven by end-user desire for sub-inch accuracy and the ability to return to the same point in a field year over year.

In reality, these systems have been in existence for more than a decade, getting their start in the construction and surveying industries. RTK systems have found a home in ag because the resulting accuracy allow users to perform accuracy intensive tasks such as strip-till. In addition, the efficiency benefits – running machines through the field after dark, reduced operator fatigue – have served to reduce the payback time on these systems.

“RTK allows farmers to achieve superior accuracy by bring the correction source to the farm or field area,” says Ryan Pieper, product manager, GPS and sensors for Trimble.

Utilizing a permanent base station, a high-end receiver and antenna on the tractor or rig, and a satellite GPS signal, RTK delivers sub-inch accuracy that is fully repeatable as long as the base station is in a fixed position. This nearly “absolute” accuracy has attracted a lot of attention among growers and retail service providers alike.

Growers have had two points of entry for getting into RTK systems – either purchase a system on their own, including a permanent base station, or get on board with a retailer, cooperative, or their service provider that has constructed an RTK tower network by paying a yearly subscription fee.

Often, it has been the cooperative or independent retailer that’s constructed the network system in partnership with progressive growers, and offered a subscription based signal. The advantage of the tower network is the service aspect – when the system has problems, the servicer provides support. In addition, the tower network provides a signal that is always on, and less of an investment than a full blown stand alone RTK system.

On the other hand, with the stand alone system there is the benefit of ownership, allowing the individual user to upgrade or modify the system as they see fit.

Experts generally agree that anything less than an RTK system will probably never be able to match the RTK system inch for inch. Still, with a price point of around $20,000 for an RTK system, there is still a significant market for products with excellent accuracy at a more modest price point. This market will be the target of the cool new developments coming in satellite based global positioning.

Revolution Evolution

It seems like an eternity, but it’s only been about a decade that satellite based differential correction has been available to agriculture. The first five of those years, the U.S. government’s GPS slipped an intentional error into the signal called selective availability, or SA. Companies that delivered GPS to agriculture were forced to create subscription-based solutions to correct the intentional accuracy error.

In 2000, with the Cold War essentially over and the Gulf War past, the government ended SA, and was simultaneously funding a new positioning project called the Wide Area Augmentation System (WAAS). Built to support future use in aviation, the signal also doubles as a free and reliable alternative GPS source for a variety of industries, including agriculture. Officially launched in 2003, WAAS provides GPS correction for a wide range of farm field tasks that don’t require pinpoint accuracy.

Up to now, there haven’t been any truly revolutionary developments in satellite-originated GPS, but there are a number of initiatives in the works – some available now – that will bring more accuracy options that approach the accuracy of RTK systems.

The GPS constellation of satellites based in the U.S. and the WAAS system have been providing the lion’s share of differential correction for American agriculture up to now. But methods of boosting the accuracy of GPS, as well as the addition of new satellites from outside the U.S. are making, or will make, greater accuracy without the use of an RTK-style base station possible.

“Improvements in SBAS differential corrections should provide more robust sub-meter solutions within the next 2 years,” says John Bohlke, product marketing manager, Hemisphere GPS. “That includes increasing the WAAS network to better cover the extreme latitudes in North America and a fully operational EGNOS for European users.”

Signal provider OmniSTAR has already released two new options to its traditional VBS correction, OmniSTAR XP and HP, which have gained wide acceptance by GPS receiver manufacturers. The XP and HP signal options provide pass to pass accuracy of 6 inches and 4 inches respectively, is available virtually anywhere, and is not tethered to a base station.

On the other hand, the system does not improve the issue of convergence time – the time it takes a system to regain a signal after it has lost it, a significant time eater. Still, as a very accurate GPS solution it suffices for many tasks, such as automatic steering.

Longer term, modernization of the satellite constellation is in the works, which among the upgrades will include the availability two new civilian GPS signals. The signals, L2C and L5 will offer more robust signals and a position solutions that is more reliable and more accurate than is currently available, according to John Pointon, marketing manager at OmniSTAR. The signals are not expected to be available for another 6 to 9 years.

More immediately, the U.S. based GPS constellation is getting a boost from GLONASS, the Russian satellite constellation.

“A partial GLONASS constellation is available now, and Russia has committed to quickly increasing the number of satellites during the next three years,” says Hemisphere’s Bohlke.

Topcon Positioning Systems, which grew its market share in the construction and surveying industry by being an early adopter of the GLONASS system in its receivers, has brought the technology over to agriculture. Its 40 channel GPS receiver is capable of using GPS or GLONASS satellite signals. More satellites means less chance of signal loss, and faster acquisition time than GPS-only receivers.

With Russia’s commitment to quickly ramp up, look for more GLONASS-ready receivers in the near future.

“More satellites means less downtime and increased positioning accuracy,” says Trimbles Pieper. “The agricultural division of Trimble is continually working to leverage available solutions from the most innovative technologies available today. These technologies include Trimble’s new line of GNSS (Global Navigation Satellite Systems) capable hardware which utilize the new L2C, L5, and GLONASS systems.”

A longer term piece of the puzzle is Europe’s Galileo constellation. “Galileo is new and will likely require 5 to 10 years before it becomes a practical solution to the precision agriculture practitioner,” says Boehlke. “New receiver designs will be implemented by all the GPS manufacturers over the next few years to allow reception of these new broadcasts and implement improved performance.”

Of course, all this additional horsepower will come at a higher price. But GPS signal providers and receiver manufacturers are clearly trying to clear up some of the issues that have long made global positioning anything but a utility one can take for granted, like flicking a switch to turn on a light.

Editor’s note: This article first appeared in the Fall 2006 issue of PrecisionAg Special Reports.

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2 comments on “GPS Yesterday, Today, and Tomorrow

  1. Nice story, but are you aware that the FCC is about to issue a waver of its own rules to a firm (LightSquared) which will set up a network of 40,000 transmitters nation-wide. Those transmitters will operateon a channel adjacent to the GPS Channel. Recent testsdemonstrated conclusively that precision GPS receivers will not operate with many miles of such transmitter sites.

  2. Nice story, but are you aware that the FCC is about to issue a waver of its own rules to a firm (LightSquared) which will set up a network of 40,000 transmitters nation-wide. Those transmitters will operateon a channel adjacent to the GPS Channel. Recent testsdemonstrated conclusively that precision GPS receivers will not operate with many miles of such transmitter sites.

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