# Feasibility of Obtaining Surface Layer Moisture Flux Using an IR Thermometer
## 1 Introduction  
This study evaluates a method whereby a single non-contact infrared (IR) thermometer can be used to obtain both the vertical gradients and fluxes of air temperature and moisture content in the first 1-2 m of air above the ground. Since the IR Thermometer primarily quantifies the emissive temperature of material surfaces within its field of view (FOV), this paper outlines methods that allow the IR Thermometer to measure objects that are representative of the thermodynamic dry-bulb and wet-bulb temperatures. Standard psychometric relationships and calculators can then be used with the obtained dry- and wet-bulb temperatures (and pressure) to obtain standard meteorological quantifications of air temperature and humidity from a single IR Thermometer. The technique used in this experiment involves an IR Thermometer and paper towel material, along with a Kestrel 4000 Weather Meter and Sling Psychrometer for validation. Infrared thermometers are used to measure the temperature of the surface in the FOV within which the pointinglaser (that typically is part of an IR Thermometer) is directed. A chief goal of this experiment is to establish how accurately a low-cost, procedurally simple, and relatively low maintenance IR Thermometer can quantify wet-bulb temperature when compared to standard psychometric wet-bulb measurements and those derived from other moisture sensing devices. The wet-bulb temperature, the temperature of an air parcel if cooled to a steady state via evaporation at constant pressure, provides a measure of the water vapor content of the air and is used to derive meteorological parameters, such as dew point temperature and relative humidity. Sling Psychometers, (sometimes denoted as \"Spsychometers\" or \"Spsych\" in this paper) are devices composed of two thermometers: one bulb is covered in a wet wick, whereas the other remains uncovered, utilized to quantify the physical and thermal properties of moist air. The dry-bulb temperature, which is essentially the ambient air temperature, is measured with the non-wick thermometer, whereas the wet-bulb temperature is obtained by evaporative cooling (a result of the slinging motion) of the moistened wick. To adequately measure the wet-bulb temperature, the psychrometer must be spun around at a speed of 2-3 revolutions per second for approximately 1.5-2 min until the wet-bulb thermometer reaches a constant value [1]. The World Meteorological Organization guidelines provide a broader range for acceptable ventilation rates, between 2.2 and 10 m s\({}^{-1}\)[2]. Inconsistencies in measurements are generally associated with insufficient moistening of the cotton wick, low spin velocities or contaminated wicks. Furthermore, Sling Psychometers can be affected by solar radiation, and measurements with direct sunlight on the thermometers during the ventilation process should be avoided. Additionally, to prevent physical damage to the device, measurements < 1 m above the ground are rarely performed. The technique to use IR Thermometers is based on the same principles used by the Sling Psychometer method and offers a fast, low risk and cost-effective method to measure temperature [3]. IR Thermometers exploit the property of all materials to emit electromagnetic radiation at temperatures above absolute zero [4]. The amount and primary wavelengths of the emitted energy are based on the temperature through Planck's Law [5; 6; 7]. IR Thermography is a measurement technique based on the detection of radiation in the IR spectrum, generally in the ranges of 2.0-5.6 and 8.0-14.0 \(\upmu\)m [5]. These two spectral bands are commonly utilized because atmospheric absorption is relatively small, thus enabling sufficient broadband radiation to reach the sensor.