Farming is a complex business which involves managing variables such as weather, soil and crop inputs to ultimately maximize yield and minimize waste and cost. As population growth continues to increase, so do demands on our food supply. Today, more than ever, farmers rely on technology to manage their fields in order to optimize productivity.
Global Navigation Satellite Systems (GNSS) integrate with agricultural machinery to serve a critical role in precision agriculture. At a basic level, these systems help farmers keep rows straight and ensure that the spacing of seed and application of other inputs like fertilizers, herbicides and fungicides are applied with minimal gaps or overlaps. The benefits of high accuracy GNSS positioning are well known throughout the agriculture community and contribute to the optimization of land use and resource application.
Predictive analytical software, for example, allows farmers to identify zones of variability within their fields so that they can be managed appropriately at the micro level. A farmer can increase seed density in a particular zone where water and crop nutrients may be more plentiful, while reducing seed density in another zone that has fewer resources to sustain plant growth—all based on GNSS positioning.
Farmers around the world increasingly rely on higher accuracy positioning systems to work more efficiently in their fields. Stand-alone GNSS data needs additional corrections to reduce system errors and deliver higher positioning accuracies. Early on, these accuracies were achieved using either Real-Time Kinematic (RTK) or Satellite Based Augmentation Systems (SBAS) like the GPS Wide Area Augmentation System (WAAS). However, in recent years, there has been a rising trend in precision agriculture towards the use of Precise Point Positioning (PPP) solutions to meet this demand. PPP is a positioning method which provides better accuracy than WAAS and simplifies equipment requirements when compared to RTK, where separate communication links are required. While PPP is not a new idea, recent receiver technology and GNSS advancements have significantly improved the performance of PPP solutions, making this a viable alternative to RTK for many precision agriculture users.
When employing PPP, the error sources are mitigated by combining satellite orbit and clock correction data with error modeling in the receiver, resulting in sub-decimetre accuracy. The GNSS hardware requirements for a PPP solution are limited to only a single receiver on the machine, using globally applicable corrections that provide the same performance anywhere in the world. Correction data is delivered via satellite to the same receiver used for GNSS signal tracking and does not rely on proximity to ground network infrastructure.
The NovAtel Advantage
PPP performance has been steadily improving; in some cases rivaling the performance of RTK based systems that provide centimetre-level accuracy. NovAtel CORRECT™ proprietary algorithms on NovAtel’s OEM6® GNSS receivers were developed to optimize the performance achieved using TerraStar-C correction data. Utilizing data from both GPS and GLONASS satellite systems, TerraStar-C corrections combined with NovAtel CORRECT’s error modeling, enables positioning accuracy as good as four centimetres—more than sufficient in most cases for planting crops such as corn and soybeans, in addition to other precision agriculture applications. NovAtel CORRECT also optimizes other key performance criteria, including initial solution convergence and re-convergence times.
As mentioned previously, machine guidance systems using NovAtel CORRECT with PPP do not require local base-station infrastructure, including cellular modem, Wi-Fi, or other radio data links. Fewer hardware requirements can translate into significant investment savings for the agriculture producer. The savings are even greater in remote areas, where local base stations, cellular services and Internet connectivity required for RTK operation might not exist. While RTK still offers premium accuracy and immediate solution convergence, the combination of minimal equipment needs and a globally accessible solution make PPP a complimentary alternative to RTK for many precision agriculture applications.
By partnering with TerraStar for its PPP offering, NovAtel customers benefit from the reliability and quality of an established service. TerraStar infrastructure and data products are built on 20 years of expertise and backed by fully redundant and independent data centers with delivery of data over multiple satellites. In addition, TerraStar provides service flexibility that can help farmers manage their operating costs throughout the growing seasons. Typical subscriptions cover one, three, six, or 12 months which means a farmer who requires a high level of accuracy for spring planting only, does not have to subscribe to the service for a full year.
PPP: Matching Performance to Application Requirements in the Field
Gofex, a small, family-owned contract farming company in Liptovské Vlachy, Slovakia, has reduced its planting time by employing PPP-based systems. This has allowed field equipment operators to keep an eye on planting, not on the row markers, increasing planting precision.
Gofex, which provides services such as corn planting, silage processing and harvesting, has found decimetre-level accuracy to be sufficient for their needs. This year, responding to customer demand for straight crop rows, Gofex began implementing precision agriculture for the first time. Jaroslav and Peter Urban had Ag Leader install its GPS 6500 receivers, based on NovAtel hardware and software, OnTrac3 Assisted Steering systems and Compass displays on the Claas Axion and New Holland T7.250 tractors. Gofex uses an eight-row Kinze 3500 and a six-row Kinze 3000 for planting.
PPP is a better option for Gofex than RTK, the Urbans believe. Slovakia is a small country, but its terrain varies widely, from lowlands near the border with Hungary to the south, to mountains in the north. Cellular reception also varies widely throughout the country. With TerraStar-C PPP, Gofex can obtain initial convergence—the length of time required to obtain a decimetre-level position solution from a “cold start” of the GNSS positioning—at times in less than 10 minutes. More importantly, if tracking lock on a minimum number of satellites is lost in the field, the system reinitializes within seconds to provide continued positioning. Field tests indicate that the NovAtel CORRECT system can regain sub-decimetre accuracy almost instantly following short outages.
Having used the PPP system for a few months, the Urbans have high confidence in the system’s accuracy. At first, Peter Urban randomly checked the system’s performance with a measuring tape by simply measuring the distance between the rows. Later, he occasionally used field markers for visual checks. Because the PPP-guided performance met the tolerances of these methods, he no longer needs to check as often.
As a result of their experience with the Ag Leader GPS 6500 system, the Urbans believe that the higher customer satisfaction that results will equate to more work for the company in the future.
Help from Above
Another method of differential GNSS positioning that has attracted a following among farmers over the years is the use of a SBAS, such as WAAS established by the U.S. Federal Aviation Administration.
PPP delivers a much more reliable and accurate solution than WAAS for Guy LaRochelle, owner of LaRochelle Farm in Zenon Park, Saskatchewan, and operator of an Ag Leader dealership. The Ag Leader positioning system with the embedded NovAtel PPP solution he installed on his Case IH Patriot Series sprayer last spring required much lower setup costs than the RTK system he had begun using a few years earlier.
For about 25 years, LaRochelle has managed a 2,000-acre farm, which produces wheat, canola, peas and canary feed. Having worked in the computer industry before coming back to take over the family farm, he has a deep understanding of the benefits of technology for optimizing his business. Precision agriculture is not a new concept for LaRochelle; he previously used WAAS for machine guidance and then set up the infrastructure for more accurate RTK several years ago.
“RTK is very expensive when you start putting up towers and so forth,” he says, adding that his own customers would have had to do the same to use that technology. “Customers were having a hard time justifying spending $30,000 to start RTK.”
And, while WAAS is free, the sub–metre accuracy it provides is not sufficient for most precision agriculture applications. So, this past spring, he had his sprayer configured with the Ag Leader GPS 6500 system utilizing TerraStar system to see if he could enjoy better-than-WAAS accuracy. The GNSS configuration also includes Ag Leader’s Integra monitor and Steer Command automated steering system.
“I put it on my sprayer because I use the sprayer throughout the year; I can monitor it better, whereas if I put it on my drill, I can only use it for a few weeks in the spring,” LaRochelle explains.
After a few months, it became clear that the accuracy is better than with WAAS. “Most people don’t need inch accuracy in our area, unless they want to do some ditching where they need elevation accuracy,” he says. “But most of the time, accuracy to within three to four inches [about 7–10 centimetres] is enough.”
Soon after having the system installed, LaRochelle would check its accuracy by setting up two parallel lines of flags, the width of the sprayer’s tires, in a section of his land. During the spring, he would run the sprayer via the guidance system, and the sprayer stayed within the flag lines every time, he reports.
“That’s how I was able to tell how consistent it was,” he says. “I have never turned it on and run over the flags because the accuracy was off. It’s not quite as accurate as RTK but that’s the nature of the beast.”
LaRochelle still repeats the tests from time to time. “Sometimes I go back and spray in that same field and try to follow the same tracks so I’m not making new tracks and trampling crops,” he says. “I just create a new job with my old pattern, and it pretty much falls into that same track every time.”
He adds that he inadvertently crushed more plants using WAAS-based positioning due to its lower accuracy.
“I think [PPP] is a very, very good system for farmers who don’t need inch accuracy but still want something more accurate than sub-metre accuracy like you get with WAAS,” LaRochelle says. “For the price you pay for the signal, I think it’s a very, very good alternative versus something like RTK, which involves expensive equipment and may be something that you’d need for elevation.”
LaRochelle reports that NovAtel CORRECT with TerraStar PPP is actually more reliable than RTK for his purposes: heavily wooded eastern Saskatchewan presents challenges for RTK systems, such as reliable transmission and reception of correction data from local base stations. Convergence time is very short if the sprayer is started up in the same location as it finished the previous day, longer if it is moved prior to startup, LaRochelle says.
A Southern View
Jaime Vivo, who has been working on his family’s Los Macachines farm in San José, Uruguay, for more than 20 years, reports that he has obtained the maximum precision that PPP can achieve: three to four centimetres. Between the family farm and clients’ rented fields, he manages about 3,000 hectares (7,410 acres) of soy, wheat, barley, corn and sorghum.
He has practiced precision agriculture for a total of about four years, having previously used a GNSS receiver from Müller-Elektronik GmbH for spraying. The accuracy of the Müller system, combined with e-Dif differential corrections, was about 25 centimetres. About a year ago, Vivo worked with Carlos Cabral, a product support specialist with Ag Leader Brazil, to have the Ag Leader GPS 6500 system with TerraStar installed on a Case 9370 tractor.
Cabral points out that two issues affect system accuracy: overall correction signal accuracy and the tractor’s steering system, which compensates for field topography. Because Vivo’s fields are on flat terrain, Cabral says that topography was not really a factor.
Last year, Vivo watched the NovAtel TerraStar-C system in action while Cabral planted wheat rows spaced 20 centimetres apart. To check accuracy, Cabral measured the distance from one pass to the next. Based on about a dozen measurements over the course of three passes, Cabral determined that the accuracy was within three centimetres almost invariably, four centimetres at the most. Such precision was adequate for planting rows based on 20-centimetre centres.
“The operator works more comfortably and relaxed and, at the same time, I can rely on the operator and on the results,” Vivo says.