Point of Beginning

Cultivating GNSS

October 27, 2011


It’s come a long way in a short time. In the mid-1990s, GPS was moving into the surveying mainstream. Post-processed static or kinematic methods using briefcase-sized receivers were the primary techniques for GPS surveying, which focused heavily on control and geodetic applications. As manufacturers introduced GPS field surveying equipment that was smaller and simpler to operate, the cost-to-productivity ratio rapidly improved, and applications grew to include topographic mapping and data collection as well as cadastral and control. GIS professionals began to engage the productivity and accuracy of the new systems, as well.

For the GPS positioning community, the availability of local, accessible control points was a key concern. The work to establish control needed on a job site often added time and cost to a project, and GPS users began to look for convenient, local control points to provide the basis for their measurements. In many areas, surveyors, utilities or government agencies installed permanent GPS reference stations known as Community Base Stations (CBS) or Continuously Operating Reference Stations (CORS). Users could access GPS data from the CBS for post processing with static or kinematic surveys.

By the end of the decade, real-time techniques were available for both surveying and mapping applications. To support these users, CBS operators could broadcast real-time differential (RTD) or real-time kinematic (RTK) correction data using a UHF transmitter connected to the GPS base station equipment. With this technique, a single base station could support multiple, independent crews. The era of broad-based real-time GPS positioning had begun.

While a CORS provides important benefits for local DGPS or RTK users, it can cover only a limited territory for real-time service. DGPS operations are typically limited to 60 to 120 miles (100 to 200 km) around a reference station, and RTK users seldom operate more than 12 to 18 miles (20 to 30 km) from their base stations. This limitation was solved in the early 2000s, when the emergence of real-time GPS networks (RTN) and widespread wireless telecommunications made it possible to provide centimeter-level positioning services over large geographic areas.

Photo credit: Accufarm, Ltd.

Canada, which has nearly 3.8 million square miles (10 million square km) of land area, is the second-largest country on earth, behind only Russia in geographic size. Providing positioning services at the meter and centimeter levels for the entire country is a daunting proposition. In the late 1990s, Cansel, a Vancouver-based distributor of surveying and construction positioning equipment, recognized the need for GPS reference data and began to install GPS reference stations on its offices. Originally intended to supply regional RTK, DGPS and data for post processing, Cansel’s initial collection of fewer than 10 CORS has grown into one of the largest and most widely used GNSS positioning networks in the world. It’s helped make Canada a world leader in precise, real-time positioning.

Known as Can-Net, the Cansel network includes more than 250 Trimble GNSS receivers connected to a central service center in Calgary. According to Can-Net business development manager David Janssens, Can-Net is a hybrid system, designed to provide both network RTK positioning services and single-base corrections. The network uses Trimble VRS technology to provide real-time positioning to more than 1,000 subscribers in nine provinces. Can-Net’s first VRS network began serving the Toronto area in 2005. Today, Can-Net includes seven distinct Trimble VRS networks that deliver network RTK solutions in key urban areas and industrial corridors. In outlying areas, individual CORS--also tied to Can-Net for communications and data sharing--supply data for single-base RTK. Can-Net users receive corrections via the Internet using cellular technology and NTRIP (Network Transport of RTCM via Internet Protocol). All of the network’s operations are controlled using Trimble VRS3Net App software.

Surveyors and mappers aren’t the only people embracing satellite-based positioning and navigation. As applications and demand for precise GNSS continue to grow, Can-Net has expanded and densified to serve new geographic areas and new types of users. One of the most important needs for positioning lies in Canada’s immense capacity to produce food.

Agriculture and agri-food industries play a major role in Canada’s economy. The country is the world’s fourth largest exporter of agriculture products, enjoying a 2009 net import/export surplus of $7.3 billion. In 2009, the industry employed 2 million people and accounted for 8.2 percent of Canada’s Gross Domestic Product (GDP). Farming and primary agriculture alone contributed 1.7 percent of GDP.

Because they lie at the heart of the agri-food system, the performance of Canadian farms affects the entire food supply chain. The potential benefits of using GNSS in agriculture are enormous. Some examples include:

• Guidance and control of farm equipment. On a modern farm, one of the most basic and important skills is the ability to drive tractors and field equipment in straight, consistent rows, and to reproduce those rows throughout each growing season. While it seems simple, accurate steering requires a high level of concentration. It is a core component of a successful farm. One of the first agricultural applications of GPS was a simple lightbar system to instruct the driver to steer to the left or right.

• Application of seed and treatments. Precise positioning eliminates gaps or overlaps in seeding and application of fertilizer and weed and pest controls. It can prevent the application of products to headlands or other non-producing areas. This optimizes the use of the land and reduces a farm’s costs for seed and other products.

• Performance monitoring and variable rate technology. By connecting GNSS to yield monitors on harvesting equipment, farms can develop detailed maps of a field’s performance. Based on this information, operators can use variable rate technology (VRT) to control the application of seed and treatments at any location in the field. Low-producing locations may receive additional fertilizer, while high-producing areas need less. Overall, the field’s production improves, and the cost of treatment goes down.

GPS (and now GNSS) is not new to agriculture. It’s common to see systems using the Wide-Area Augmentation System (WAAS) or subscription services such as OmniSTAR to provide DGPS corrections. But higher precision provides even greater benefits. While yield monitoring on large farms can work with positions accurate to a few decimeters, most applications require tighter control, and a growing number of farms have turned to RTK. Many farms have operated their own reference stations to achieve RTK performance and precision.

At Forthdale Farms near Lynden, Ontario, Kenny Forth is a third-generation family farmer who grows broccoli on 220 acres. Forthdale owns two tractors, each equipped with Trimble AgGPS Autopilot automated steering systems that provide position and steering to the sub-inch level. Forth uses RTK GPS to plant, spray and cultivate his fields. During planting season, Forthdale workers manually set young broccoli plants into the earth from the rear of the planting machine. The GPS steering ensures straight rows, and Forth plants about 10 acres per day compared to 8 acres without GPS. “It’s a bit quicker,” he says, “and much more efficient. I’m getting more plants in the ground per acre than before I started with GPS.”

Photo credit: Trimble

As the plants grow, GPS lets Forth cultivate to within 1 inch (2.5 cm) of his plants while driving at 6 miles per hour (10 kph). The technique lets him remove more weeds and cultivate closer to the broccoli plants than could ever be achieved with manual steering. For spraying, the steering systems prevent gaps or overlap and avoid spraying in areas where product is not needed. In 2010, the first year Forthdale used GPS for spraying, the farm saved roughly $10,000 on fertilizer alone. “The key is to plant straight rows,” Forth advises. “The rest of the year hinges on that. Our rows are in the same place every year. It maximizes the spray and we don’t spend as much money.”

Forth operated his own RTK base station for four years. He was pleased with the precision and repeatability of GPS, but operating his reference station posed some problems. Terrain and vegetation in southern Ontario forced him to use radio repeaters to deliver the RTK signals, and he encountered issues with communications reliability. And when Forth wanted to upgrade his steering systems to support GLONASS, he learned he needed to buy a new base station receiver, as well. Instead, he turned to Can-Net and the Trimble VRS network solution.

The transition was easy. Rather than receiving RTK corrections from the farm’s base station via UHF radio, Forth’s tractors use cellular telephone technology to connect to the Internet and receive RTK data from the real-time network. He uses the Trimble Autopilot with GLONASS on both tractors, and keeps a GPS-based lightbar system on hand as a backup.

In southern Ontario and across Canada’s Prairie Provinces of Alberta, Manitoba and Saskatchewan, it’s not uncommon for a farm to cover thousands of acres. Larry Prong, a GPS specialist for Premier Equipment in Elmira, Ontario, said that commodity pricing on large-scale (or “broadacre”) crops such as corn, soybeans and other grains makes them very cost sensitive. While the large farms can benefit from the accuracy of RTK, their sheer size makes a single-base approach unwieldy. The distance from the base station to the rovers in the fields can stretch the limits of RTK, and terrain and vegetation often interferes with the 900 MHz radios commonly used on Canadian farms. Prong estimates that more than 70 percent of the large farms in his area use GPS, although many still use WAAS corrections. Prong believes that they are prime candidates for network solution RTK.

One of the benefits of agricultural GPS systems is the reduction of operator fatigue. In addition to driving the tractor, the farmer must tend to the mechanical systems attached to it. With automated steering, the farmer can concentrate on the seeders, sprayers and other equipment, and not worry about keeping straight, accurate rows. The GPS and GNSS systems also make it possible for less-experienced operators to produce consistent rows and applications. These and other benefits provide savings that can more than pay for the cost of the network subscription.

The demand for precise positioning in agriculture presents a paradox for RTN operators. In order to serve the farming regions, a GNSS network must cover a large area that contains a small number of subscribers. To provide geographic coverage, manage the costs and ensure quality service, Can-Net often partners with local or regional suppliers of farm machinery and supplies. Janssens says that the local dealers have the relationships with the farm operators and intimate knowledge of each farm’s unique needs. A dealership can provide the physical needs (site, power, communications) for a reference station, and can develop its staff to provide the technical knowledge needed to install and support GNSS equipment on farm machinery.

With the emergence of more applications for precise positioning, Can-Net expects its rapid growth to continue. There are plans in place for an additional 100 reference stations to serve new regions. Janssens notes that the growth rate for agricultural subscriptions is more than 100 percent annually, and he expects the trend to continue. Derek McGill, senior GNSS technician for Mazergroup, a New Holland dealer in Killarny, Manitoba, believes that GNSS has already taken hold. “Farmers originally thought that you had to have a big operation to use GNSS,” he said. “But around 90 percent of the farms in my area have some sort of GNSS. The large operations often use auto-steering connected directly to the machine hydraulics, and smaller ones have lightbars or basic steering systems.”

As Can-Net continues to expand, it will attract clients from an even broader base of applications. These new clients will bring different expectations. The network’s early users, primarily surveyors and positioning professionals, wanted detailed information on the performance of the network. They used the information to document the accuracy of the measured positions and to compare the VRS technology with static and single-base RTK. While the need for positioning accuracy has not diminished, new users are shifting the requirements more toward the reliable operation of the network. Most users and local dealers understand that reliable cellular communications is essential to precise positioning via the RTN. The dealers work with local cellular providers to develop suitable coverage and capacity for wireless Internet access.

Many applications need positioning data to be available on a 24/7 basis. Harvesting operations often run continuously for several days, and any network downtime can be disruptive and costly to the farmers. The Can-Net operators understand this and work to prevent any problems related to the operation of their GNSS receivers, network servers and software. Can-Net plans its major system maintenance with the seasonal nature of the users in mind. But it’s a balancing act. While the winter months may be slow periods for Canadian farmers, some surveying, logging and other operations work at full speed to take advantage of winter’s frozen ground.

McGill and Janssens both point to the requirements for higher accuracy in agricultural positioning as a driver for growth in RTK networks. Many farms started using GPS with satellite-based augmentation systems (SBAS), which provided precision of 6 to 8 inches (15 to 20 cm). That’s often sufficient for same day, pass-to-pass consistency. But high-value crops, variable rate techniques and erosion reduction practices demand long-term repeatability at the centimeter level. It’s producing a busy, if not stressful, challenge for Janssens. “I’m learning about things I never dreamt of,” he says. “It’s just a very exciting business.”