Drones, or Unmanned Aerial Vehicles (UAVs) are seen by many as a new, transformative tool used in precision agriculture. The UAVs potential lies in the ability to quickly capture snapshots of information needed by farmers to help assess and manage current agronomic conditions. A UAV can quickly scout large sections of field to help identify and pinpoint such things as nitrogen stress, early signs of insect damage, disease and water stress.
“An initial economic report put out in March 2013 by the Association for Unmanned Vehicle Systems International (AUVSI) estimates that as much as 80-percent of the potential market for UAVs is in agriculture,” reported Rob Austin, researcher and Geographic Information Specialist at North Carolina State University in Raleigh, who received a grant from the Golden Leaf Foundation to study the use of UAVs in precision agriculture and their use in nitrogen management.
Austin is working on how to interpret the data received from the small multi-spectral sensors and cameras mounted on micro UAVs into actionable information that farmers can use to make more informed decisions. However, not enough work has been done yet to know the true benefits UAVs will have in agriculture, according to Austin. “My responsibility as a good researcher is to put data behind the claims and provide unbiased information. So far we can say, this technology looks great and we can easily capture on-farm images, but can we use those images to guide better decision-making? Some things that seem possible now might materialize and some probably won’t. I don’t expect a more widespread use of UAVs in agriculture until at least 2018.”
So far, Austin and his team of experts in related fields have been running regular micro UAV flights over a 7-acre study plot of wheat and have begun flights over a 5-acre test plot of field corn. “Every time we fly, we learn more about both the capabilities and limitations of these systems.”
In order to validate UAV data during every flight, the team members take leaf samples to test in a lab for nitrogen content and use a field spectrometer to measure spectral reflectance on the ground. “We are working on validating what we see in the air with measurements on the ground. The goal is to correlate the data collected from the sensors mounted on the UAVs that measure the amount of light the plants are reflecting and absorbing to the amount of nitrogen that is actually in the plant tissues.
“When the wheat is harvested, we’ll record yields from our different treatment areas and compare how the yields correlate with the nitrogen status of the plants as visualized by the UAV images and as shown in the tissue tests.”
The 5-acre corn trials will include irrigated and non-irrigated plots to compare how water stress affects the images taken by the UAV. “The theory is that plant stress can be detected by a multi spectral camera or a thermal sensor before you can see it with your eyes,” commented Austin. “Ideally, one day it may be possible to pinpoint, with UAV images, early signs of plant stress from insect infestation or disease, so the farmer can spot-treat sections of the field before the outbreaks become more generalized.
“The big question is can we quantify what we see in the images to make informed decisions on the ground? The ultimate goal of the study is to provide the initial groundwork necessary to make possible the use of UAVs in day-to-day farm operations,” said Austin. As part of that goal, they are studying the ability to detect early season nitrogen deficiencies using UAV-based imagery and whether a farmer can take corrective action based on that imagery to prevent yield loss.
Austin continued, “What we’re trying to do is to tie an optical response (from the UAVs multi-spectral cameras and sensors) to a tissue nitrogen value (as show by the tissue testing), to a growth stage, to the amount of nitrogen that is vital to optimize yield.” That’s a tall order!
“It’s not just a matter of ‘This part of the field looks greener’, we have to quantify what ‘greener’ means. We need to know if a farmer can perform an action, based on UAV data, to maximize his yields or prevent yield loss. I’m particularly interested in nitrogen because it can potentially leach out of the root zone and it is important to crop growth.” It would be helpful to have a quick way to determine the crop needs.
The grant was awarded for 18 months. The first eight months were spent acquiring a Certificate of Authorization (COA) from the FAA. In order to obtain the proper certification, North Carolina State worked with the Next Generation Air Transportation (NGAT) center located on Centennial Campus in Raleigh. NGAT is helping guide the integration of Unmanned Aircraft Systems (UAS) into domestic airspace in North Carolina and helped secure the proper permissions from the FAA and the state of North Carolina to perform this research.
Since the grant runs out at the end of 2015, the team is hoping to extend it for another year to further fine-tune what they’re seeing from the UAVs sensors and how it correlates with tissue testing and yielded data.
UAV’s make possible timely information gathering at a comparatively low cost. If, for example, a farmer is thinking about applying nitrogen in the next day or two, he may be able to call in a UAV company first. The UAV images can literally “read” the plant status of the field foot by foot. The sensors may show that different sections of the field need different amounts of nitrogen, maximizing yield potential while minimizing fertilizer cost and environmental risk.
Some practical issues remain to be solved. “We’re testing the capabilities of the drones themselves,” continued Austin. “We’ve found that if we fly at 300 feet, to get complete coverage with our sensor we need to fly the UAV in transects 90 feet apart. This gives us good overlap so we can stitch together images into a complete picture of your field. “But what many people don’t realize is the short flying times of many rotary-type UAV’s before their batteries need recharged. The flying time is further shortened when they are weighted down by sensors, gimbals, and other aerial photographic equipment.”
The fixed wing type of UAV, which looks like a miniature aircraft, can fly for up to 2 hours. These systems can survey thousands of acres but need a larger area for take-off and landing. With newer, turnkey type systems the need for an experienced pilot is quickly becoming a thing of the past.
Fortunately, the miniaturization of sensors and cameras is proceeding rapidly, and the newer, smaller ones weigh less, increasing flying time.