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What’s Better, Satellite Or Aerial Imagery, And Do I Need Sub-Inch Accuracy?

One of our precision experts, Warren Bills, president of Agri-Trend Geo Solutions Inc. based at Calgary, Alta., tackles your toughest precision questions. There’s much to consider when deciding between buying satellite images or booking a local plane operator to capture a bird’s eye view. Warren offers up the pros and cons of each type and, more importantly, what to do with the images (hint: don’t just look at them). Then it’s on to RTK sub-inch accuracy. Just what is it good for?

Question 1:

I want to order some “in-season imagery” for capture this growing season to use for variable rate. What are some good options and what would I do with it?


There are a few choices for in-season imagery for variable rate and a few considerations when choosing what image will work best for you. One of the best proven options is high resolution aircraft imagery. The reason this option proves favourable is because we have the most control over when and where we get the images captured. Simply put, you can order an image, task a flight and receive a high quality image back in a short period of usually 24-48 hours. It’s best to place orders early in the season so that flights can be planned around major weather systems, storms and cloud interference. With these products, because there is direct contact with the pilot, it is possible to react and capture quickly during window of opportunity. Some examples of in-season aircraft imagery would include CropCam, Prairie Agri-Photo, and Agri-Trend Real Shot.

The next best option is a frequent cycle satellite product. Because we don’t have the remote control ourselves on the satellite constellations, we are relying on the orbiting cycle, daylight hours and atmospheric conditions to be ideal for a capture. Some lower resolution satellites revisit every 14 days, so if you hit clouds on the day it’s over your field, you are nearly 28 days between captures. This isn’t ideal if you are looking for in-season imagery for decision making and application. A newly launched satellite constellation by German based company RapidEye is unique in its ability that it has five satellites in asynchronous orbit and is able to revisit nearly every five days during daylight hours and capture three to five images per season. It’s also offering high five meter resolution at an affordable price for agriculture.

With satellite in-season capture you are playing the odd’s a little bit, but look for options that will work in your favour. There have been years in the past that have been so cloudy, satellite imagery has failed to capture useable imagery.

Once you’ve made your choice of in-season imaging there are a couple key things to do with this image. The first seems simple, but often overlooked — get to the field with the image! This is the biggest opportunity you have with an in-season image and will help you avoid mistakes of misinterpreting a dense vegetation area as “crop” when it’s weeds, or assuming that the cause of variability and problems is the same across all corners. This process is called “groundtruthing” and can be as simple as taking a printed copy of the image, or as technical as loading up an image to a GPS handheld device or computer and navigating around.

The next key thing when you are out their is to record the observations and tests for the application you are thinking of varying.

Here are some examples:

1) If you are thinking of VRT fungicide in canola, run through the sclerotinia check list, examine plant populations, percentage bloom and sclerotia in the field or nearby fields.

2) If you are thinking of VRT foliar fertilizer, equip your toolbelt with a SPAD meter, tissue sampling gear and good diagnostic skills

3) If you are thinking VRT pesticide for weeds, brush up on the weed identification, take out a threshold chart and find the ideal time to spray based on varied staging.

4) If you just want to learn more for fall work, visit the high and low vegetation areas, take compaction readings, hand textures and setup your sampling spots for the fall.

In-season imagery will soon be just one of those things that accompanies a good farm plan. Targeting scouting and sampling with the aid of an image provide value alone. Taking that information and turning into VRT applications is where the best bang for the buck can be derived. So as spring is here remember these things:

1) Choose an image capture product that will get you the desired delivery time and cloud free capture back in your hands quickly

2) Choose a resolution that will allow you to identify the smallest micro trends and observations when ground-truthing

3) Choose a product with a format that is geo-referenced or can be, so if you need to apply VRT application with zones, things go much quicker.

Use these tools to your advantage and avoid pretty pictures at the end of the year. If you know more, you’ll grow more.

Question 2:

Everyone’s talking RTK. What are some reasons I need to be SO accurate?


Autosteering machinery today with corrected signal subscriptions seems to be providing pretty decent accuracy under four to six inches pass-to-pass. For most of our seeding and spraying operations this is pretty darn straight and accurate. Now with RTK corrected signals through networked locations becoming more freely available and affordable, the question of why and when to upgrade is more common. There may be a few of us that want the RTK “just to have it,” but most of us are looking for the other advantages and capabilities that RTK level accuracy (less than one inch) will bring us. Here are a few ideas to get started:

1) Inter-row seeding. This is the number one reason that producers seem to relate to as the immediate opportunity. With an ability to place seed between last years stubble you begin to gain control over factors such as seed bed quality and consistency with more consistent seed placement, improved weed control with a consistency in crop competition across the field between the rows, reduced inter-row competition for water, nutrients, and sunlight and consistent plant heights, trash control and harvestability

2) Precise fertilizer placement. The opportunity for fall banding of nutrients and the spring application of seed near or around that fall band is realistic. With sub inch accuracy, treating and seeding into zones of optimal nutrient uptake becomes easier. Dribble banding high rates of post emergent fertilizer precisely around plants avoids some of the risks of phytotoxicity.

3) Controlled Traffic Farming (CTF). Although maybe a couple years out for us, we can get started today with moving towards a controlled traffic system. The use of RTK for controlled traffic in countries such as Australia, New Zealand, and parts of Europe is proving to be valuable for reducing compaction, maximizing on inter-row input applications with more ease, and improving water infiltration.

These three opportunities with RTK have and will yield a return. They won’t occur overnight and need proper planning and strategy, but they will make the RTK investment yield more of a return. Other uses for RTK include reducing overlap and over application of inputs, optional high-speed data in the cab, and maybe even a concept of inter-row cultivation. Food for thought, yes?

Have a precision farming question you need answered? Terry Aberhart and Warren Bills are here to help. Send your questions to editor Lyndsey Smith ([email protected])or by calling 306-731-3637, and she’ll pass them along.



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