ARS | Publication request: Evaluation of a wireless infrared thermometer with a narrow field of view

Submitted to: Computers and Electronics in Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 22, 2010
Publication Date: April 30, 2011
Citation: O'Shaughnessy, S.A., Hebel, M.A., Evett, S.R., Colaizzi, P.D. 2011. Evaluation of a wireless infrared thermometer with a narrow field of view. Computers and Electronics in Agriculture. 76(1):59-68.

Interpretive Summary: Infrared thermometers are an important tool for the remote measurement of plant canopy temperature and soil. Researchers typically use hand-held infrared thermometers for spot measurements or wired infrared thermometers connected to a data logger if continuous measurements are needed. However, using a hand-held sensor is time consuming, and the ability to manage wired sensors becomes difficult in the case of monitoring large fields or making changes once the sensors are established. Wireless infrared thermometers will increase the convenience and scalability of continuous measurements; however, their availability is limited. We developed a prototype wireless narrow field-of-view infrared thermometer. Our interest in a wireless non-contact temperature sensor with a narrow FOV is to provide accurate remote monitoring of row crops. The temperature readings of the wireless sensors compared well to known targets and measurements made by a commercial hand-held thermometer and wired infrared thermometer. Additional testing is required to investigate the consistency of the temperature measurements in the outdoors over a cropped field.

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, applications for these non-contact thermometers employed the use of hand-held or stationary industrial infrared thermometers (IRTs) wired to data loggers. Wireless sensors in agricultural applications are a practical alternative, but the availability of wireless IRTs with an open communication protocol is limited. In this study, we designed prototype narrow (10 degrees) field-of-view wireless infrared sensor modules and evaluated their performance by comparing temperature readings of an object (T obj) against a blackbody calibrator in a controlled temperature room at ambient temperatures of 15, 25, 35, and 45 degrees centigrade. Additional comparative readings were taken over plant and soil samples alongside a hand-held IRT and a wired IRT. The average root mean square error (RMSE) and mean absolute error (MAE) between the collected IRT object temperature readings and the blackbody target ranged between 0.13 and 0.59 degrees centigrade, respectively. The average RMSE and MAE between measurements from the hand-held and wireless IRTs over soil and vegetation samples was 0.27 and 0.50 degrees centigrade, respectively. The wireless IRT also compared well to the wired IRT, with RMSE = 0.50 degrees centigrade and MAE = 0.55 degrees centigrade. Additional tests were performed to investigate the influence of solar radiation on sensor body temperature. Locating the sensor within a white plastic sleeve provided ample reduction in heat transfer imposed by direct radiation such that sensor readings were not unduly affected (RMSE = 0.04 degrees centigrade, MAE = 0.42 degrees centigrade, and mean bias error (MBE) = 0.09 degrees centigrade compared with a RMSE= 0.04 degrees centigrade, MAE = 0.36 degrees centigrade, MBE = 0.08 degrees centigrade for the sensor in the aluminum housing). Because of their measurement repeatability, these wireless prototype sensors have the potential to be utilized in outdoor agricultural applications. Further studies are needed to test the performance of the sensors in a network system over a cropped field.