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Thermal imaging sensors capture an object’s long wave infrared radiation using thermal detectors (i.e., micro bolometers). Thermal sensors with radiometric options acquire images with each pixel as a temperature data point. Thermal imagers’ form factor and costs are decreasing rapidly. However, further improvements are needed for acquiring high-resolution and noise-free data. By nature, temperature change is very dynamic and can change swiftly due to wind or cloud cover. Moreover, sensor temperature can affect the accuracy of the data. Such data is harder to normalize and its interpretation in agricultural crop monitoring should be done cautiously.


Data analytics A range of commercial solutions from offline post-flight data processing to the cloud-based data upload for storage, data processing and presentation are available. Some software can be purchased at a one-time cost (plus annual upgrades) or can be an annual subscription to data managers. Concerns related to online cloud-based services exist due to data ownership, privacy, and unintentional or without consent sharing of such data.


What does this mean for


irrigated crop management? Different sensors can be integrated with a UAS for scouting irrigated crops. It’s the sensor output type that determines its suitability for a given application. For example, in irrigated fields (e.g., potato, corn, mint, tree fruit and grapevine crops), high-resolution RGB imagery


can be used to determine the early signs of crop vigor variations.


A combination of multispectral and thermal imagery can also be used to determine crop water use and abiotic stress and to detect leaks in the irrigation system. Thermal imagery is especially useful for detecting crop water stress since plants that are not fully transpiring are relatively warmer than those that are.


Drone imagery provides a high level of spatiotemporal data that suits many projects related to irrigation water-use monitoring. For example, as Washington State University teams retrofit or develop new irrigation techniques/ methods suitable for a given crop and site, multispectral and thermal drone imagery was found to evaluate the site-specific suitability of such techniques (see figs. 1 and 2).


Overall, the domain of integrating various types of imaging sensors with small UAS is changing rapidly in terms of capabilities and cost. Major validation of these sensors for specific agriculture applications are needed for their meaningful use. The industry also needs to develop and offer robust sensor data analytics and processing to help growers in making more informed, real-time crop management decisions.


Lav R. Khot, PhD, is an assistant professor at the Center for Precision and Automated Agricultural Systems, Irrigated Agriculture Research and Extension Center at Washington State University.


R. Troy Peters, PhD, PE, CAIS, works for Washington State University and serves as the extension irrigation specialist at the Irrigated Agriculture Research and Extension Center.


Figure 2. A small UAS imaging low elevation and mid- elevation spray application irrigated corn on 134 days after planting (bottom left). The results include a thermal image (bottom right) and a normalized difference vegetation index image mosaic (below) of the study area. (Project is funded by State of Washington Water Research Center; investiga- tors: L. Khot and R.T. Peters, Washington State University.)


24 Irrigation TODAY | April 2018


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