Modeling Diurnal Canopy Temperature Dynamics Using One‐Time‐of‐Day Measurements and a Reference Temperature Curve

Abstract

climate-dependent threshold time, then an irrigation event of a fixed depth is scheduled (Fig. 1). Evett et al.The application of the temperature-time threshold (TTT) method (1996, 2000) demonstrated in drip-irrigated plots that of irrigation scheduling to self-propelled irrigations systems requires a method of estimating the diurnal canopy temperature dynamics automatic irrigation using the TTT method was more using only a one-time-of-day measurement. Other research efforts responsive to plant stress and showed the potential to such as the crop water stress index (CWSI) and field canopy temperaoutyield manual irrigation scheduling based on a 100% ture mapping using moving irrigation systems could also be served replenishment of crop water use as determined by neuby the use of this method. This was accomplished using a stationary tron probe soil water content measurements. It is desirreference measurement to capture the canopy temperature dynamics.able to apply the TTT method to moving irrigation sys-Two different methods were developed for estimating a temperature tems such as center pivots or linear-move systems. curve for a remote location from a one-time-of-day measurement at However, infrared thermometers (IRTs) mounted on that location. The first method (scaled method) uses the ratio between moving irrigation systems provide only one-time-of-day the reference temperature and the remote location temperature, refermeasurements. This necessitates a method of estimating enced to the predawn temperature, to scale the reference curve to yield the predicted curve. In the second method (Gaussian difference the diurnal canopy temperature dynamics using only a method), a three-parameter Gaussian equation was empirically fitted one-time-of-day canopy temperature measurement. to the temperature differences between the reference and the mea-Other canopy temperature-based crop stress indicasured remote canopy temperature curves. To test these two methods, tors such as the Crop Water Stress Index (CWSI; Jackcanopy temperature data, sensed using stationary infrared thermomeson, 1982) are sensitive to the time of day that the meaters, from three different crops {corn (Zea mays L.), cotton (Gossypsurements are taken (U.S. Water Conserv. Lab., 2004). ium hirsutum L.), and soybean [Glycine max (L.) Merr.]} were ana-There is also an increased interest in quantifying spalyzed. For a few hours after dawn and before sunset, the scaled method tially varying crop response to soil-, water-, disease-, or was generally more accurate while during the middle of the day, the

A crop water stress index and time threshold for automatic irrigation scheduling of grain sorghum

“…Crop canopy temperatures recorded from the moving irrigation system were averaged for the period of time it took for the system to move across each plot, and so represented a mean one-time-of-day plot-specific temperature. These plot-specific temperatures were scaled using the method of Peters and Evett (2004) to produce estimates of the plot temperature over the entire daytime. Wind speed (u z ) and solar radiation (R s , W m −2 ) were measured every 2 s at a height (z) of 2 m (using a RM-Young Wind Sentry Set and LI-COR 200SZ, respectively) using a datalogger (model CR10X, Campbell Scientific, Logan, UT) located in plot 12 ( Fig.…”

Wireless Sensor Network Effectively Controls Center Pivot Irrigation of Sorghum

“…Because the pivot was moving when canopy temperature measurements were obtained, the center pivot passed over each plot during different times of the day, requiring a method to determine canopy temperature, T s , throughout the daylight hours for each remote measurement. We used the scaling procedure described by Peters and Evett (2004) …”

Two-Source Energy Balance Model to Calculate E, T, and ET: Comparison of Priestley-Taylor and Penman-Monteith Formulations and Two Time Scaling Methods

“…With surface temperature typically measured at only one time of day for a given location, it is nonetheless possible to model diurnal surface temperature using the temperature scaling method of Evett (1989) and Evett et al (1994). This method was used by Peters and Evett (2004), who reformulated it for arrays of infrared thermometers aboard center pivots, which pass over different locations of the field at a single time of day, similar to satellites. The method has been successfully used to schedule center pivot irrigations and control crop water productivity for several crops, where the data thus generated were applied to algorithms such as the time-temperature threshold and time-integrated crop water stress index (e.g., Peters and Evett, 2008;O'Shaughnessy et al, 2011O'Shaughnessy et al, , 2012.…”

“…The time scaling methods were based on reference ET (Colaizzi et al, 2006) and a modeled diurnal surface temperature (Peters and Evett, 2004). Each time scaling method was tested using surface temperatures measured at five different times of the day.…”