Thermal Imaging in Crop Management
Farmers are always keen to discover new methods to produce more crops and lower the water usage for irrigation purposes. The US Department of Agriculture (USDA) has undertaken research activities on irrigation and water management. The researchers are using thermal imaging cameras from FLIR Systems (Figure 1) to quantify water stress and analyze water productivity.
Figure 1. The FLIR A655sc provides 14-bit data up to 50 frames per second at full frame 640 × 480 resolution.
When a plant does not receive the required water supply, the leaves begin to wither; this is called ‘water-stressed’. Farmers have to provide water on a larger scale to produce several commercial crops. They will also have to consider climate variability and risks, such as decreasing aquifers (underground water layers), low water reservoirs, and water right issues between states.
The USDA research team aims to assist farmers to be highly productive using minimal water. To achieve this, they induce stress on crops and observe the water stress. They take into account a number of factors such as precipitation, irrigation, and soil conditions. The team also wants to find alternative methods of irrigation management. One example is deficit irrigation, which is an optimization strategy where irrigation is used during drought sensitive growth stages of a crop. The rest of the time, irrigation is reduced or not even required if there is sufficient rainfall.
Colorado is known to be the region for corn. Crops such as sunflower and wheat are also grown here. The USDA Water Management Research Unit runs the Limited Irrigation Research Farm (LIRF) (Figure 2) near their HQ in Fort Collins (CO). LIRF consisting of 96 corn and sunflower plots of 9 by 44m. In these test fields, the USDA team is applying 12 different irrigation treatments.
Figure 2. The Limited Irrigation Research Farm (LIRF) consists of 96 corn and sunflower plots of 9 by 44 meters. In these test fields the USDA team is applying 12 different irrigation treatments. While applying several irrigation treatments, the USDA is monitoring these crops in three different ways: at plant level, remotely by satellite and by means of ground-based remote sensing.
Dr. Kendall DeJonge, agricultural engineer at the USDA, explains the research project in detail. The team monitored the crops (corn and sunflower) in three different ways while applying USDA’s irrigation treatments (Figure 3). At plant level, they remotely monitored using satellite, and ground-based remote sensing. Thermal imaging cameras from FLIR are used for the latter.
Figure 3. Several irrigation treatments are compared throughout the crops’ various growth stages.
To detect crop water stress remotely, the optimal and proven technique is via the measurement of canopy temperature or a crop’s surface. The correlation between water stress and surface temperature is based on the assumption that as a crop transpires, or ‘sweats’, the evaporated water cools the leaves to a temperature below that of air temperature. When the crop reaches water stressed level, the leaves begin to curl and transpiration decreases, leading to an increase in leaf temperature.
Next to permanent IR thermometer installations, the test field is also observed twice per week using a GPS-referenced tractor, which is fully equipped with sensor material, including an RGB camera, an IR thermometer, a FLIR A655sc camera, and a multispectral camera (Figure 4). The whole equipment is attached to a boom, which is mounted on the tractor.
Figure 4. Next to a FLIR A655sc camera, the USDA team also makes use of an RGB camera, an IR thermometer, a multi-spectral camera and a GPS. All this equipment is attached to a boom that has been mounted on the tractor.
Dr. DeJonge states that IR thermometers were used before as they were economical; however they are not capable of providing an image. The team chose a thermal imager for this project. High resolution was required as the researchers needed to look closely at the difference between water-stressed plants and plants with adequate water supply. The researchers also needed separate ground temperature and plant temperature, and observe the difference between non-shaded leaves and shaded leaves. A FLIRrepresentative provided a demo, and then the team chose the FLIR A655sc research camera for the project, as it met all of the requirements.
The FLIR A655sc offers 14-bit data up to 50 fps at full frame 640 × 480 resolution. The thermal images of sunflowers taken by the team using it clearly revealed the flower head (Figure 5) was hotter and the leaves were 5° colder. Also, the veins of the leaf were observed to be hotter than the rest of the leaf.
Figure 5. Thermal images captured by the FLIR A655sc present clear temperature differences between the flower head and the leaves, and between the leaf veins and the rest of the leaf.
The FLIR camera is also very robust. It was able to handle the hot weather and dusty environment.
Figure 6. A thermal image clearly shows the difference between crops with full irrigation treatment (top) and limited irrigation treatment (bottom).
The FLIR thermal imaging camera was able to provide the team with an indispensable means of data collection. The team has now been using the thermal imaging cameras for three years and has been able to formulate a wide data set. Using the results produced from the FLIR thermal imaging camera, the team will be able to make informed decisions on irrigation.
The article has highlighted the importance of using FLIR camera models to study crops and better irrigation of crops. Today, research facilities like the USDA are using advanced FLIR camera models. It is also possible that farmers themselves could make use of these gadgets and the thermal imagery. Dr. Kendall DeJonge says that going forward he hopes farmers can use handheld thermal imagers to assess water stress by themselves.