# Feasibility of Obtaining Surface Layer Moisture Flux Using an IR Thermometer
## 2 Methodology
### Experimentation
The total time required to take all measurements over the various surfaces was approximately 30 min; therefore, environmental changes that occurred over the measurement cycle created subtle yet occasionally noticeable differences in data. As noted earlier, the IR Thermometer technique was applied during freezing conditions to evaluate the capability to measure ice-bulb temperature (trials 54-62 in Appendix A). Numerous attempts were made to use a walk-in freezer for testing; however, due to COVID-19 restrictions, this option was not available for experimental analysis. Therefore, experiments were conducted in the freezer of a standard-sized refrigerator. A Sling Psychrometer was not used due to limitations of the freezer space. The Kestrel and wet paper towel were placed in the freezer with the door closed for 45 s to acclimate to the extreme temperatures. Ice-bulb temperature was measured first with the IR Thermometer after opening the door to limit warm, higher moisture air intrusion into the freezer environment. However, this often yielded wet-bulb temperatures that exceeded the dry-bulb measurements, presumably due to deposition and/or condensation on the wet/frozen paper towel that resulted in latent heat release on that towel that did not affect the dry paper towel or dry Kestrel moisture sensor nearly as much. Data from the Kestrel were quickly recorded after the ice-bulb temperature was measured. Although it is possible to have ice-bulb temperatures higher than the dry-bulb temperatures in environments saturated with respect to liquid water, the differing Kestrel/IR results strongly suggest that  
Figure 1: Images of the instrumentation used to conduct and validate the infrared psychrometry experiment: (**a**) Control: Bacharach 0012-7012 Sling Psychrometer; (**b**) Control: Kestrel 4000 Weather Meter, and (**c**) Test: Centech infrared thermometer (also known as IR Thermometer). a walk-in freezer or below-freezing outdoor conditions are necessary to validate that the IR sensor technique can be applied in zero and sub-zero \({}^{\circ}\)C conditions. The means and standard deviations of the measured dry-bulb and wet-bulb temperatures obtained from the three instruments over the three different surface types are shown in Figures 2-4. Note that the depicted daily mean and standard deviation temperature measurements derived by each method are superimposed on each method's final daily measurement. Results from preliminary trials demonstrated that the IR Thermometer technique could be utilized to quantify wet-bulb temperature and thus was expanded to determine its applicability to quantify vertical variations in wet-bulb temperatures, yielding a novel technique to measure moisture flux. As seen in Figure 5, paper towels were positioned on a wooden pole at several heights (i.e., 28, 46, 64, 81 and 99 cm) above ground level in a grassy, shaded area. As before, measurements were taken at various times of day and under varying sky conditions. The Kestrel was the only device used for validation measurements at each height, as the Sling Psychrometer is not a practical instrument to differentiate wet-bulb temperatures at relatively small height increments all within a meter of the ground. Figure 2: (**a**) Individual observations, as well as the daily means and standard deviations (superimposed on the final daily observation) of dry-bulb (DB) temperatures as measured by the Kestrel, Sling Psychrometer and IR Thermometer over concrete. (**b**) Individual observations, daily means, and standard deviations of wet-bulb (WB) temperatures as measured by the Kestrel, Sling Psychrometer and IR Thermometer over concrete.