TECH CORNER
CANOPY TEMPERATURE MEASUREMENT
By Ken Sudduth, PhD L
The MSICC could provide another alternative for producers wanting to schedule irrigation based on temperature measurements of crop stress.
ike other aspects of agriculture, irrigation management has entered the information age. More and more, producers are adopting sensor-based decision-making
as they look to increase efficiency and cut costs. Irrigation scheduling based on plant stress, often by comparing crop canopy temperature to air temperature, is one well-researched approach. Usually, the canopy temperature is obtained from an infrared thermometer (IRT) above the crop at one or more places in a field.
A problem with using an IRT is that it gives an integrated temperature measurement of everything in its field of view. This may include more soil than crop — especially early in the growing season — resulting in data that are not representative of the true canopy temperature. To solve this problem, our research group in Columbia, Missouri, developed a low-cost prototype sensor that can ignore the temperature of the noncrop background and provide the temperature of just the canopy.
The MSICC
The research group, with representatives from the University of Missouri and the U.S. Department of Agriculture-Agricultural Research Service, developed the Multi-band System for Imaging a Crop Canopy (shortened to MSICC) using low-cost, readily available electronic and imaging components. The MSICC includes two cameras; one captures visible images, and the other is a long-wave infrared (LWIR) camera to obtain temperature images. An interface
June 09 13:39 CDT
board with an imbedded microcomputer controls the cameras, capturing and storing image data.
The MSICC works by using the output of the visible camera to separate the crop portions of the image from the parts that are bare soil or residue. This “mask” is then used to remove the noncrop portions of the LWIR image. Finally, a calibration, accurate to 0.65 degrees Celsius (1.17 degrees Fahrenheit), is applied to calculate the temperature of the crop portion of the LWIR image. Because the MSICC gives an image, temperature variability across the canopy can be obtained, along with the average.
Current status
Field tests showed that the MSICC is able to remove shaded areas and soil from thermal images and provide temperature measurements more representative of the active part of the crop canopy. The MSICC is currently in prototype form, and more work is required before it is ready for use. Several improvements to the hardware and software of the system are needed, as are long-term field tests to evaluate its robustness and function under varying environmental conditions. If it passes these hurdles, the MSICC could provide another alternative for producers wanting to schedule irrigation based on temperature measurements of crop stress.
Ken Sudduth, PhD, is a research agricultural engineer in the USDA-ARS Cropping Systems and Water Quality Research Unit in Columbia, Missouri.
Image median: 39.69°C, IRT: 39.97°C Segmented median: 30.83°C
Left: visible camera image; center: LWIR image with calibration applied; right: image of crop only, after removal of background
30 6 Irrigation TODAY | Winter 2020 35 Temperature (°C) 40 45 50 30 35 Temperature (°C) 40 45 50
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