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Irrigation management with infrared thermometry.

Infrarcd thermometry was introduced into agriculture I more than 40 years ago as a hand-held tool to remotely I measure the surface radiometric temperature of crops. H Using optics and specialized detectors, these sensors were engineered to filter thermal radiation in the mid- to far-infrared region (typically in the 8 to 14 urn portion of the electromagnetic spectrum) and were integrated with a battery power supply and electronics to convert the transducer signal to a digital temperature display or a low-voltage output for recording. Spot measurements of crop canopy surfaces were used to characterize water stress in plants, predict yields, and manage irrigations.

In recent years, engineering advances in infrared instrumentation have led to self-powered infrared thermometers (IRTs) that allow easier direct recording with electronic data loggers and, thereby, continuous crop surface temperature monitoring. Similar technologies are used in orbital satellites to monitor the Earth's surface temperature. Unfortunately, the satellite systems are handicapped by a large pixel area and long, infrequent overpass cycles, which render them inadequate, at present, for the real-time field-scale measurements required for precise irrigation management.

A new application for a proven technology

At the USDA-ARS Conservation and Production Research Laboratory in Bushland, Texas, research work on automatic control of pressurized irrigation systems based on canopy temperature was initiated in the early 1990s. Remote spatial and temporal crop monitoring was accomplished by locating sensors within a field and by mounting IRTs and a GPS receiver on a center-pivot lateral. The resulting crop yields of corn, soybean, and cotton achieved with automatic irrigation scheduling were as great as or greater than those obtained with traditional irrigation scheduling using neutron probes for soil water content sensing.

Development of a scaling algorithm allowed site-specific, once-a-day crop surface temperature measurements taken from a moving irrigation system to be converted to a curve of canopy temperature for the daylight hours at any particular site. This led to a second important application of infrared thermometry: the development of whole-field, once-a-day canopy temperature maps that could be related to a water stress index, leaf water potential, soil profile water content, potential yield, and the detection of out-of-control management zones that required special attention.

The availability of affordable integrated circuits, microcontrollers, and wireless communication devices has made it easier to establish outdoor wireless sensor networks. By using wireless sensor networks and a moving sprinkler lateral as a platform for remote sensing, the problems and costs associated with deploying and maintaining cables across a field are eliminated. Although there are still advances to be made in the areas of reliability, power consumption, and maintenance, work to advance the application of wireless sensor networks in irrigated agriculture will undoubtedly lead to reliable, practical, integrated systems.

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Wireless IRTs

Currently, work at Bushland uses wireless sensor networks for automatic irrigation scheduling and control of center-pivot irrigation systems. IRTs are being developed by designing electronic circuits to interface with off-the-shelf infrared detectors and radio-frequency transceivers using the IEEE 802.15.4/ZigBee protocol. The use of an open communication protocol allows incorporation of other ZigBee-com-patible sensors developed by various manufacturers into the sensor network system without the added expense of specialized receivers and additional interface software at the base station. Each sensor is powered by its own battery pack, and a solar panel is used to recharge the batteries.

Applications for the future

By mounting the wireless IRTs, routers, and a GPS unit on the center-pivot lateral, a wireless sensor network is established to monitor within-field crop water status as the pivot moves and consequently control irrigation. The combination of wireless sensor networks on the irrigation laterals, temperature scaling, spatial and temporal crop water status maps, and automated irrigation control are a solid basis for site-specific irrigation management. We expect to advance this site-specific irrigation system toward commercialization by combining the mature technology of infrared thermometry with the convenience of modern wireless communication to allow transparent implementation of advanced irrigation automation algorithms.

ASABE members Susan O'Shaughnessy is a research agricultural engineer (Susan.0'Shaughnessy@ars.usda.gov), Steve Evett is a research soil scientist (Steve.Evett@ars.usda.gov), and Terry Howell, Sr., is research leader (terry.howell@ars.usda.gov), USDA-ARS Conservation and Production Research Laboratory, Bushland, Texas, USA.
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Author:O'Shaughnessy, Susan; Evett, Steve; Howell, Terry, Sr.
Publication:Resource: Engineering & Technology for a Sustainable World
Date:Sep 1, 2011
Words:701
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