Volume 2, Issue 3
Missouri Precision Agriculture
Center
257 Agricultural Engineering Building
University of Missouri
Columbia, MO 65211
Phone: (573) 882-1138
Fax: (573) 882-1138
E-mail: mpac@missouri.edu
Internet: http://fse.missouri.edu/mpac
MPAC is a partnership of:
MU College of Agriculture, Food and Natural Resources
University Outreach and Extension
USDA Agricultural Research Service -- Cropping Systems
and Water Research Unit
MPAC is supported in part by Outreach Development Funds, University Outreach and Extension
In This Issue
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Several new products have recently hit the market that takes advantage of the wide area augmentation system (WAAS). WAAS is a differential signal source broadcast by the FAA that is similar to the Coast Guard’s beacon.
New GPS receivers from John Deere, AGCO, Trimble and Satloc are all designed to receive the new free WAAS signal. The John Deere StarFire boasts 6ft accuracy using WAAS, but the FAA reports improving GPS accuracy in general to approximately 21 feet. Older Satloc SLXg and SLX300 receivers can also be updated with firmware to receive the signal.
However, WAAS has hit a snag. Originally scheduled to be fully operational by the fall of 2000, WAAS testing and certification has been pushed back to sometime in 2002. According to an article by Dee Ann Divis in the May 2000 issue of GPS World, testing by the FAA has indicated that the system may have problems in two areas: stability and integrity.
While the new receivers on the market do not rely solely on WAAS for a differential signal, but rather offer it as a low-cost feature and also as a backup signal, integrity issues with the signal are problematic. Apparently the WAAS program found that the system’s processors were letting erroneous information slip by and this brought into question the integrity of the entire system.
To make matters worse, funding for WAAS is expected to be cut by congress. Meanwhile, the signal continues to broadcast and can be picked-up by a WAAS configured DGPS receiver. The question remains whether or not the signal is reliable for precision agriculture.
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New Chair of Coordinating Committee Elected
At the last MPAC coordinating committee meeting in June, Dr. Bill Wiebold announced that he would not be able to continue as chair for the next fiscal year. By unanimous vote, Dr. Newell Kitchen was elected by the committee as the new chair. He accepted the two-year appointment and will assume duties as of July 1, 2000.
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New Precision Agriculture Tools
There are several new offerings in precision agriculture tools that incorporate improved GPS receivers. The biggest breakthroughs have been in autopilot systems and soon to be released GPS driven irrigators.
More Accurate DGPS Receivers
New DGPS receivers take advantage of multiple differential signals. In addition to subscription services that cost approximately $500/year for one signal and $800/year for two signals, and the Coast Guard beacon, there is the new free Wide Area Augmentation Different combinations of differential signals offer greater accuracy and backup if one signal is lost.
John Deere’s GreenStar system has switched exclusively to L-band technology and will no longer support C-band. However, they will swap C-band receivers for L-band receivers at no cost. Customers can also upgrade to the new StarFire for only $600.
Trimble is offering a GPS
receiver combined with an antenna in a single, lightweight unit called the
AgGPS 114 DGPS Smart Antenna which eliminates the need for a connecting
cable. It can be used with any precision farming device.
GPS Driven Irrigators
According to a recent article by John G. White in Farm Industry News, Lindsay Manufacturing and Valmont Industries both have prototype GPS corner system and lateral system irrigators that should be on the market with in a year.
The GPS receiver is mounted on the pivot tower and offers
4-8" accuracy. The systems eliminate the need for buried wire which
makes them suitable for a wider range of terrain. They can also cover up
to 14 percent more acres than the buried wire systems.
The main obstacles are expense
and slow uplink time. Lindsay Manufacturing is working to develop a
product that can be retrofitted to their existing line of Zimmatic
irrigators, offsetting the cost of an entirely new system.
GPS Guided Tractors -- Autopilot Systems
Three companies have unveiled autopilot systems for tractors that connect GPS to an electronic steering mechanism. IntegriNautics offers the AutoFarm system ($38,000) and from Australia is the Beeline Navigator ($50,000). Trimble Navigation’s autopilot system should be on the market with in the year.
Autopilot systems can create perfectly straights rows for approximately six miles with one-inch accuracy, thereby eliminating the need for application overlap. Systems can also be operated day or night and in any type of weather because the autopilot eliminates the need for the operator to have visual contact with the field.
According to an article by Harry Cline for Farm Press, producers have had a very positive response to the new systems. They report that the systems are user-friendly and that it only takes five minutes to set up the portable GPS antenna at the side of the field. They also said that having a no-hands operation makes projects go much faster.
On the downside, the
systems are expensive and cannot be hooked up to hydraulic steering.
Lightbar Guidance Systems
For those who can’t afford to shell out the bucks for an autopilot system, the new light bars may the next best thing. They offer 6-12" accuracy and most can be programmed to set swath pattern, swath width, and start and end points. The driver simply needs to keep the light in the middle of the display to stay on track. Systems are often bundled with a data logger so critical information on what was applied where can be kept. Wag Corp, Trimble and SatLoc are offering systems that cost between $2,000 - $13,000.
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Can a $300 GPS Receiver Be Used for Precision Ag?
On May 1, 2000, President Clinton ordered that Selective Availability (SA) component of the civilian Global Positioning System signal be discontinued. Selective Availability was the government’s way of intentionally degrading the accuracy of the signal. Discontinuing SA immediately improved GPS accuracy from 300 feet to 60 feet. With some hand held GPS receivers, an accuracy of 15 feet is obtainable. The question asked is, is this accurate enough for precision agriculture?
A preliminary study conducted by Kent Shannon, associate director of the Missouri Precision Agriculture Center, shows the possibility of using a $300 GPS receiver for data collection. It all depends on how accurate you want the location to be relative to where it actually is in the field.
For this preliminary study, a Garmin GPSIII receiver and a Trimble Ag122 DGPS receiver were used. The Trimble GPS receiver used a Coast Guard beacon signal for differential correction. Data was collected from the Trimble receiver using a palmtop computer running FarmWorks Site Mate data collection software. Data was directly collected to the Garmin receiver.
The test was conducted during crop scouting of two fields in west central Missouri. Data collected included stationary points and contour paths. From the stationary data, 17 points were collected with both receivers, the difference between positions ranged from being within 2 feet of each other to 40 feet. The average difference was 24 feet with a standard deviation of 11 feet. These results show that if one wants to mark areas of weed escapes or wet spots, being within 24 feet would probably be accurate enough. However, if you were collecting soil samples, you would still need a DGPS receiver. When collecting data on a contour path, it was obvious that the receiver without differential correction could not be used for yield monitoring (Figure 1).
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Need more information about subjects in this issue of Precise News? Find it on the web at these addresses. Don’t forget to look at the updated MPAC website.
• MPAC
• WAAS and GPS
• Selective Availability
• GPS World
• Farm Industry News
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