# Feasibility of Obtaining Surface Layer Moisture Flux Using an IR Thermometer
## 2 Methodology  
### Experimentation  
In this research, the dry-bulb temperature was measured by pointing a Centech infrared thermometer at a dry paper towel approximately 15 cm away, a distance in which the paper towel completely fills the measurement spot defined by the Centech's optical resolution [3]. By ensuring the paper towel completely filled the viewed spot, there was no additional thermal radiation sampled from the background environment, which could degrade the accuracy of the temperature measurement. To measure the wet-bulb temperature, the paper towel was wetted with water, and a handheld fan was oriented perpendicular to it to maintain airflow into the wet towel for up to 1 min to create proper ventilation and thus evaporative cooling. Similar to the guidelines associated with accurate Sling Psychrometer measurements, IR Thermometer data were collected in shaded conditions to avoid sunlight contamination. Experiments were conducted during the summer of 2020 near the University of Dayton campus, located in Dayton OH (39.7589\({}^{\circ}\) N, 84.1916\({}^{\circ}\) W). Dry- and wet-bulb temperatures were measured in various atmospheric conditions and over various surfaces (e.g., grass, concrete, sand), which influence those same atmospheric conditions. Experiments were conducted at different times of day and sky cover, as well as during rain events, to determine the applicability and limitations of the IR Thermometer technique. Simultaneous measurements were collected with a Bacharach Sling Psychrometer and Kestrel 4000 Weather Meter, which are shown in Figure 1. These instruments provided validation data. Dew point temperature, relative humidity and barometric pressure data were also collected by the Kestrel for comparisons to parameters measured and derived by the IR Thermometer and psychrometer. Relative humidity and dew point temperature were evaluated using psychrometric relationships and Bolton's equation (covered in Section 2.2). Data collection procedures consisted of measuring atmospheric variables (e.g., dry-, wet-bulb temperature, pressure, relative humidity) with a Kestrel, followed directly with the IR Thermometer and Sling Psychrometer. Initial trials were conducted with a two-person team under a covered patio. While one individual held the paper and directed the airflow from the handheld fan toward the paper towel, the other person took temperature measurements by pointing the IR Thermometer at the center of the paper towel from approximately 15 cm away. Sling Psychrometer measurements were made by spinning the device around for approximately two minutes at the same height above the ground in which the paper towel was held. Experiments were conducted in an outdoor, open environment. Shade was found to be a critical prerequisite, as is generally sought for psychrometer measurements, to ensure that sunlight and thus solar heating did not affect the data. The instrumentation required time to become acclimated to the surrounding environment; it was noted that the IR sensor yielded inaccurate measurements after being relocated from a warm to a cool environment or vice versa [3]. Eventually the experimental setup was modified to require only one individual to conduct measurements; this was conducted by securing paper towels to the arms and base of a lawn chair while allowing for unobstructed air flow from the fan to create evaporative cooling. The measurements were organized by surface type and were originally made by one device (e.g., Kestrel) over all three surfaces in succession prior to switching to another device. Subsequently, procedural modifications were made to measure temperatures above a surface with all three (i.e., Kestrel, Sling Psychrometer and IR Thermometer) instruments in succession prior to moving to another surface. This modification reduced data inconsistencies due to environmental changes occurring during the measurement period. Sand surface experiments were conducted on an on-campus volleyball court, where an umbrella was deployed to create a shaded environment.