Aerial imagery provides a way to harness data to guide field decisions
It’s hard to manage what you can’t see. That’s where aerial imagery can lend farmers a hand. Send up a drone or plane or lasso a satellite to collect a bird’s-eye view, compile available images to analyze points of interest and trends, and then set out on foot to investigate before it’s too late.
Remote-sensing technology has most commonly been used to help farmers target scouting efforts based on a curious looking spot on an image, likely due to stress from weeds, pests or nutrient issues. A new wave of technology available to farmers claims to pinpoint plant population and yield.
Farmers need to first decide what they want to see and measure and why. In turn, that will help determine the types of sensors best suited, how often images need to be collected and cost, says Isaac Ferrie, who works with the Farm Journal Test Plots program.
In the Farm Journal Test Plots, imagery comes in handy to verify data. For example, a basic high-altitude image provides a baseline reference for crop growth and the magnitude of any problem areas, Ferrie notes. Coupled with thermal and normalized difference vegetation index (NDVI) images captured throughout the season by a drone or manned aircraft, the Test Plots team can pinpoint areas of stress that need further investigating on foot.
“The goal of imagery is to help farmers be proactive, not reactive,” says Maykol Hernandez, senior agronomist and director of business development, AirScout. “A stressed crop can have issues regulating heat, just like a person with a fever, and show hotter in a thermal image.”
Thermal cameras, for example, use infrared bands to measure energy, which shows up as various colors based on temperature. When an area shows up as red, the crop is hot. “Using a handheld device, the image can then guide boots on the ground to scout the hottest part of the field, the coldest part, etc.,” Hernandez says.
NDVI uses two wavelengths, red and near infrared (NIR). The more plant material, the more NIR light reflects back to the camera. The red is absorbed by chlorophyll for photosynthesis, so the healthier the plant the less red light reflected to the sensor.
“NDVI works to highlight variability and broadly monitor crop health across the field,” says Missy Bauer, Associate Farm Journal Field Agronomist. “Areas of poor vegetative growth identified in a late-season NDVI are often correlated to lower yielding areas on the yield map.”
NDVI is an effective tool for fine-tuning management zones used in variable-rate population and nitrogen, which is beneficial in the Farm Journal Test Plots, Bauer adds.
Satellites can capture NIR to monitor crop health as well as simple images taken with a RGB filter, which show variation in the greenness of a crop. The snapshot can include a broad swath of the electromagnetic spectrum or certain parameters and analysis.
FarmShots, for example, uses satellites to provide farmers images of their specified boundaries. When an abnormality is identified, FarmShots captures the image and sends it to the farmer, explains Joshua Miller, founder and CEO of FarmShots. It’s up to the farmer to scout and determine exactly what’s wrong.
FarmShots’ goal is to get to the point the satellite imagery can detect a specific disease by comparing previous images with confirmed diseases to new images with stress, Miller adds.
The newest generation of imagery technology available to farmers is multi- and hyperspectral mapping. Multispectral imagery typically uses four to five bands in the visible and NIR spectral bands to capture images of crops and vegetation. In addition to measuring general crop health based on NDVI, multispectral images claim to detect weeds and nitrogen deficiency as well as predict yields.
For example, drone sensor manufacturer SlantRange offers a multispectral sensor with on-board image processing to provide metrics about the status, health and yield of crops immediately after a drone flight. The sensor spots the spatial and spectral patterns of crops, weeds, dead vegetation and bare soil to isolate the crop from the weeds and the background. It looks specifically at plant color and growth to detect small changes invisible to the human eye before there’s a bigger problem, says Matt Barre, director of strategic development, SlantRange.
“Using a map generated by our software, a farmer or service provider can spot a problem in the field, draw a box around that area and the software will identify other areas with the same problem,” Barre explains.
Hyperspectral imagery, offered by companies such as Gamaya, obtain reflectance spectra of plants within the visible and/or NIR range using 40 spectral bands and thermal sensors. At up to 10 times higher resolution than NDVI, hyperspectral images claim to pinpoint the exact reason why the plant is healthy or not—specific diseases, pests and weeds; nitrogen, phosphorus and potassium deficiencies; as well as crop maturity and yield potential.
In a time when margins are tight, cost makes all the difference. Imagery services can be as low as $1 per acre but up to $10 to $12 per acre for season-long service. Price depends on resolution, number of flights and more.
Because of the investment and the importance of knowing exactly what’s going on in a field, “it’s a must to put boots on the ground — every image has to be ground-truthed,” Ferrie says.
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