Every crop producer is in the same boat. All face increasing input costs and uncertain crop prices. Trying to decrease or control input costs while maintaining optimal yield potential is the challenge crop producers must address.
Over the past few weeks I have been at many of the winter meetings and farm equipment shows, and I’m seeing more growers turning to precision agriculture to help them control input costs. They are investing in precision ag tools instead of making another big capital purchase such as a larger tractor or implement. A GPS guidance system is where most producers start.
Maybe you already have a guidance system, or you might be looking into buying one for this year. All guidance systems are designed to guide or steer your vehicle and implement in the fields to reduce overlap and wasted time, product and fuel. Having said this, there are huge differences between the various guidance packages available on the market. So what does a producer need to know? A good place to start is to develop some understanding of accuracy levels and the different types of GPS signals used to attain accuracy.
We all hear about accuracy – it’s the first thing farmers ask about and retailers are quick to provide a number. But did you know that there are two distinct and very different types of accuracy that must be considered?
The first accuracy type is “Mechanical Accuracy”. Mechanical accuracy is the ability for you, as the driver, or your auto-steer to maintain a 0’00” offline distance or a 0’00” XTE Value (Cross Track Error). In other words, with a simple lightbar without an assisted steering or auto steer package, the driver’s ability to keep the machine on the indicated path is the primary factor in achieving accuracy. If you have assisted steer or auto steer capability, mechanical accuracy would refer to the ability of those components to react to the GPS information and maintain the appropriate path.
The second accuracy type is “GPS Accuracy”. This refers to the inherent accuracy of the GPS receiver and signal type that you are using. GPS accuracy is classified into 3 levels of accuracy and understanding what these levels are is important when making a guidance system purchase decision. It is critical to be sure that you are comparing apples to apples when evaluating different guidance or other precision agricultural tools.
Here are the 3 levels:
Ø 1-Sigma, GPS accuracy claim is maintained 50% of the time within listed specifications.
Ø 2-Sigma, GPS accuracy claim is maintained 95% of the time within listed specifications.
Ø 3-Sigma, GPS accuracy claim is maintained 99.9% of the time within listed specifications.
Most manufactures with guidance products on the market today have a pass-to-pass accuracy listed using the 2-Sigma level, but there are still a few manufactures that list their accuracy based on the 1-Sigma level. The difference between these two levels is significant, but hopefully now that you know and understand what to look for in an accuracy claim you will be able to compare products more effectively and equally.
Fully understanding all the accuracy issues can get quite technical, and there is still so much more that we could discuss. It’s easy to make things very complicated, but if you would like to learn more about GPS accuracy please feel free to send me an email Jordan@gpsontario.ca and I will provide you with some new website links from scientists and engineers who have spent their lives writing, testing and learning about GPS accuracy issues.
Now that we’ve talked a bit about accuracy claims and levels, the next step is to consider the different options in GPS signal, and what each offers in terms of cost, accuracy, and
In today’s agricultural GPS environment we have access to 3 main signal types. They are: WAAS (Wide Area Augmented System), WAD, which is more widely known as OmniSTAR and SF2 signal, and lastly, RTK (Real Time Kinematic).
Determining which signal type is best for you depends on the level of accuracy you require and the different tasks you hope to undertake using GPS tools on your farm. So let’s look into the accuracy for each signal type and learn a little bit about what each of them will do.
We’ll start with the signal generated by the Wide Area Augmentation System, which is a free signal. WAAS is an air navigation aid developed by the Federal Aviation Administration to augment the Global Positioning System (GPS), with the goal of improving its accuracy, integrity, and availability. Essentially, WAAS is intended to enable aircraft to rely on GPS for all phases of flight, including precision approaches to any airport within its coverage area. WAAS uses a network of ground-based reference stations across North America to measure small variations in the GPS satellites' signals in the western hemisphere. Measurements from the reference stations are routed to master stations, which queue the received deviation correction (DC) and then send the correction messages to geostationary WAAS satellites in a timely manner (at least every 5 seconds or better). Those satellites broadcast the correction messages back to Earth, where WAAS-enabled GPS receivers use the corrections while computing their positions to improve accuracy.
WAAS is commonly listed as providing “sub-meter accuracy”, but each equipment manufacturer will have their own accuracy claim, usually called the pass-to-pass accuracy rating. Farmers should know that pass-to-pass accuracy is defined as positional accuracy which can be achieved over a 15 minute window – the idea here is that this is the time it takes to travel from one end of a field to the other and return.
For many WAAS based guidance packages, this pass-to-pass accuracy can be listed from 6” – 8” or 6”–12” accuracy (assuming 2-Sigma level). This depends a lot on the filtering, and the type of receiver that is supplied with the system. Being a precision agriculture specialist and a self acclaimed GPS consultant, I spend a lot of time talking to growers and looking into their operations to find a complete system that works for them. One of the most common questions I am asked is “Can I plant corn with WAAS?” There is no simple answer for this, because of the many changing variables to consider. When asked this question, I usually respond with two questions of my own. First, “Is your equipment on your operation matched? What I mean by this is do you have a 6 row planter and a 6 row combine head? Or a 16 row planter and an 8 row head?”
If your equipment is matched then the requirements for accuracy are significantly reduced and you have some room for error and variability in your planting. The second of my two questions is “How picky or fussy are you?” You are the controlling factor in your operation; you set the limits of what is acceptable and what isn’t. If a 25” - 36” guess row of corn is acceptable when the target row spacing is 30” then WAAS might work for you but if you want a 28” –32” guess row then WAAS accuracy is not the correct signal for you.
If you are planting a broad acre crop and have 6”-8” of room for error then a WAAS signal will probably work for you. I have growers who have been planting with a WAAS signal for many years now and are getting along with the signal just fine, they still plant with their markers on their planter and use them as an in-field visual reference line. If the guidance system is right on the marker line, then they follow it. If it’s off a little then they nudge the line over and it adjusts all the following passes for them. If you don’t want to ever have to nudge your lines then WAAS will not be for you.
In Part 2 of this blog, we’ll look at the two remaining signal types: WAD and RTK.
Jordan Wallace is a partner in GPS Ontario, a North Gower, Ontario based company. He handles sales, service, and 24 / 7 technical support. Jordan is also working with Trimble Engineering to help test new products and firmware slated for future release. Jordan spends a lot of time working on new and improved ways to advance the precision ag industry. He sees improved compatibility between components and technical support as key topics. GPS Ontario is an industry leader in precision agriculture, providing specialized and compatible equipment and information for progressive producers.
Jordan Wallace
GPS Ontario
6558 3rd Line Road South
P.O Box 456 North Gower
K0A2T0, Ontario, Canada
Office (613) 489-2932
Cell (613) 229-6377
Support (613) 327-6377
Mike PPT 905*5*52389
jordan@gpsontario.ca
This commentary is for informational purposes only. The opinions and comments expressed herein represent the opinions of the author--they do not necessarily reflect the opinion of Farms.com. This commentary is not intended to provide individual advice to anyone. Farms.com will not be liable for any errors or omissions in the information, or for any damages or losses in any way related to this commentary.