Airplanes helping to Measure Evapotranspiration
Irrigated agriculture uses a large fraction of the fresh water resources around the world. In Utah, diversions for irrigated agriculture represent approximately 85 percent of the state’s water use. Typically, water use in agriculture is very inefficient, and small improvements in efficiency would save significant quantities of water that could potentially be used to irrigate more land or be diverted to other, higher valued uses (such as municipal supply).
Evapotranspiration (ET) is water in vapor form lost from a unit surface via both evaporation from the ground, and transpiration through plant leaf surfaces. ET is usually expressed as a rate of inches or millimeters per day. It is important for irrigation scheduling and water management, and is a factor for land use applications such as watershed management, water budgeting, climate and weather modeling, and even septic tank drain field design.
Since 2006, Dr. YangQuan Chen, Associate Professor of Electrical and Computer Engineering, and Dr. Mac McKee, Director of the Utah Water Research Laboratory (UWRL) have been looking at how Unmanned Aerial Vehicles (UAVs) can measure evapotranspiration. UAV-based remote sensing is nonintrusive, while ground probes, the currently preferred method of measurement, are more expensive and sparsely distributed. Each UAV is constructed of light, strong, and low-power consumption materials, including 1) a frame/wing; 2) a motor/propeller; 3) control surface/aileron and servos; 4) remote control and communication links; 5) an autopilot; 6) GPS and other navigational sensors such as an inertial measurement unit (IMU), 7) UAV payloads such as multispectrum imagers, and 8) high power density batteries.
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UAVs are low-cost, can provide near real-time data, and have better spatial resolution than satellites or commercially available conventional aerial photography. While UAVs are constructed to withstand the elements, they are usually flown during the crop growing season for purposes of acquiring ET or other crop-relevant data.
The team has enough equipment to conduct research, thanks to ongoing sponsorship and support of the UWRL, and they would like to build a hardware-in-the-loop UAV simulation platform to minimize and accelerate prototyping. Chen says the research experience is invaluable for all, and “The students are great, fully motivated, innovative engineering problem solvers. I feel very fortunate to have this great team of engineering students working with me.”
One very important outcome of Chen’s research may be in saving agricultural water usage by offering low-cost, high-resolution (both spatial and temporal), multispectral remote sensing capabilities for irrigation scheduling and real-time water management. This is enabled by the current autonomous UAV technology and compact multispectral-imager, which are both becoming more affordable.
The ability to acquire decision-relevant data on soil moisture and evapotranspiration in a timely fashion and at low cost will enable canal companies and irrigation districts in the state to provide highly detailed information to farmers about soil moisture conditions in individual fields. This would enable farmers to better manage scarce irrigation resources, and provide critical data to irrigation system operators to more efficiently manage their complex irrigation delivery systems, thereby saving water that could be used to increase agricultural output or be allocated to other users whose demands are continually growing.
In the Sevier River Basin in particular, these advances will result in additional water available for application in agriculture, and less loss from system inefficiencies. The water savings could be as much as 5 percent or more of current deliveries. In the current economy, that kind of savings is invaluable.
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Dr. YangQuan Chen
Associate Professor of Electrical and Computer Engineering
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Electrical and Computer Engineering Department at Utah State
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Dr. Mac McKee Professor, Director, Utah Water Research Laboratory
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By Jennifer M. Carroll
Published February 5, 2009