Submitted to: Computers in Agriculture International Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 6/1/2009
Publication Date: 6/22/2009
Citation: Oshaughnessy, S.A., Hebel, M.A., Evett, S.R. 2009. Developing a wireless infrared thermometer with a narrow field of view. Computers in Agriculture International Conference Proceedings,June 22-24, 2009,Reno,Nevada. ASABE publication number 701P0409e. Interpretive Summary: Infrared thermometers are widely used in agricultural applications to measure surface temperatures for crop water stress feedback and estimate changes in temperature related to crop transpiration and water evaporation. The use of wireless infrared thermometers has the potential to reduce the labor needed to deploy the sensors and maintain wired counter parts. An infrared thermometer with a narrow field of view is critical when measuring the canopy temperature of row crops or other small footprints of interest. We developed two wireless sensors having a field of view approximately equal to 10 degrees and calibrated the sensors against a target black body whose temperature was controlled between 15 deg C and 45 deg C in a temperature controlled chamber at different ambient temperatures. We found that the resulting calibrated equations generally improved the temperature reading of the two sensors. After calibrating the sensors in the chamber, we tested each of the wireless sensors in tandem with a handheld infrared thermometer against soil and vegetation samples. Both wireless sensors compared well to the readings from the handheld thermometer.
Technical Abstract: Many agricultural applications rely on infrared sensors for remote measurement of surface temperatures for crop status monitoring and estimating sensible and latent heat fluxes. Historically, these applications employed the use of stationary industrial infrared thermometers wired to data loggers. These sensors can be expensive and if wired are cumbersome to install and impractical at the commercial level. In this study, we built two prototype narrow field of view (10°) wireless infrared sensor modules (denoted a, and ß) using two different manufactured thermopiles, both self-compensating, and compared their readings against a black body surface in a temperature controlled chamber at different ambient temperatures of 20°C, 25°C, 30°C, and 40°C. Additional tests were performed to investigate the amount of thermal mass required for sensor body temperature stabilization with the thermopiles exposed to direct radiation to intentionally cause sensor heating: (1) with no housing protection; (2) while embedded in an aluminum socket and enclosed inside of a white polyvinyl chloride (PVC) plastic sleeve; and (3) enclosed only in the plastic sleeve. Sensor readings with the detectors located inside the plastic sleeve provided ample reduction in heat transfer imposed by direct radiation. Embedding the detector inside an aluminum socket did not provide any additional temperature stabilization. The two prototype sensors were compared with measurements taken with a commercial handheld IRT over samples of vegetation and soil in a greenhouse environment. The RMSE for the corresponding calibrated measurements against a black body calibrator and soil and vegetation samples were 0.12ºC and 0.77ºC for sensor module a, and 0.15ºC and 12ºC for sensor module b, respectively. Further testing and evaluation of these prototype sensors in a field application is recommended.