Utilizing Imagery in Agriculture

Brent Wiesenburger - Agtegra Director of Ag Technology Services
It seems that everywhere we look in agricultural publications now days there is another company coming online and offering low-cost, if not free, satellite imagery. While these imaging products are available today at Agtegra Cooperative through tools like the Winfield United Field Monitoring Tool or a Climate Fieldview subscription, I would like to take some time to help you understand the value of satellite and aerial imagery and how you can utilize imagery on your operation.
The most common analysis of imagery that we see used in agricultural tools today is Normalized Difference Vegetation Index (NDVI). NDVI is a measurement of plant health that is visually displayed with a legend from -1 to +1. Healthy and very healthy plants are represented with values that range from .33 to 1. This can easily be seen in the NDVI image to the right. Here is an example of a circle pivot with streaking due to plugged or restricted nozzles. Red pixels (-1 to 0) would represent very unhealthy plants, all the way up to dark green (.66 - 1) which in this case are the healthiest plants in the image.
Now that we understand what NDVI is, how is it gathered? The most common way for agriculture is by satellite, pictured above is the Landsat 8 satellite. Landsat is an Earth-observing satellite operated by the U.S. Geological Survey (USGS). Satellite imagery is the most scalable and cost-effective solution. The raw images are acquired at a 15-meter resolution meaning every 15 square meters a value is collected. These values are used in the calculation of NDVI and often resampled down to five meters when you see it in a software interface, like Climate Fieldview. There are higher resolution images available by UAV or airplane that can get as detailed as 20-centimeter pixels. This level of detail could be used to literally count plant stands or identify weeds. UAV imagery is less scalable–a single image is 220' x 220' and requires stitching many images together in order to see a single field. This means it is more expensive to acquire due to flight time and image processing. Aerial and UAV imagery is great for on demand flights when an image is needed during a strict timeline. A single Landsat 8 satellite image is 114 miles wide which is 2,736 times larger than a typical UAV image, so you can see why satellite imagery is the go-to product for agriculture, but, a drawback is timing. Every 16 days the satellite takes a new photo of your field–cloudy or not! So, we may or may not have a usable image.

How can you utilize satellite imagery on your farm?
Let’s start with pre-season. Imagery and yield tend to have a high correlation; thus, it can be used with other layers of data like elevation or electrical conductivity in the creation of a management zone map to drive nutrient recommendations as well as seeding prescriptions, like MZB here at Agtegra.
Moving into the spring season, take a look at images as they are collected to keep an eye on how your field is developing. Many times, imagery will detect areas to scout for weed pressure (high image values early season - dark green) or regions that may need to be replanted due to spring challenges (low image values early season - red). Another valuable and often overlooked way to utilize imagery is pivot monitoring. Look at all available images throughout the growing season to see trends that indicate poor performance of nozzles or improper operation.
June is the best time to take advantage of imagery. Be sure to look at the big picture on your operation when looking at imagery! Are you ahead of average in rainfall? Are you tracking ahead in growing degree units? Imagery may be a great option to enhance crop performance with additional macro- or micro-nutrient applications in high to medium yield potential areas and not applying in low yield potential areas. Imagery can even be utilized to develop a binary (on/off) application map in order to apply crop nutrient or crop protection products where they will generate the greatest ROI. The Top Profits Soybean program available from Agtegra has an option to utilize imagery in 2019. Ask your agronomist for more information about this program.
As with any technology, verification of data is the key to success. Pictured to the right is a Winfield United R7 imagery layer with scouting pins dropped on top of it. These are used for directed tissue sampling to help you and your agronomist make in season nutrient management decisions. In this example, samples will be collected from high, medium and low potential areas of the field. When scouting, we may find other attributes contributing to plant stress like disease pressure or pest infestations. In either case, an application could be made to mitigate plant stress and add to your bottom line.
Imagery is widely available with technology tools from Agtegra. The Winfield United Field Monitoring Tool is available to you free of charge, or Climate Fieldview offers complementary imagery as well with a paid subscription. If you are interested talk to your agronomist today or email us at agtechnologyadministrator@agtegra.com. I would be glad to provide you some UAV imagery during the growing season or answer any other questions you might have. Give me a call at 605-725-8329 or email me at brent.wiesenburger@agtegra.com.

April 15, 2019 flooding in Brown County (Red=Water)

Plugged nozzles on a circle pivot

Sentera NDVI & NDRE sensor used on Agtegra UAV's

Yield Map on the left showing great correlation to the satellite image on the right

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