# Feasibility of Obtaining Surface Layer Moisture Flux Using an IR Thermometer
## 5 Conclusions  
This study describes a lower-cost, time-efficient method to obtain psychometric wet- and dry-bulb temperatures using an infrared thermometer, hand-held fan and paper towels. It also demonstrates the viability of replacing multiple, vertically-stacked dry- and wet-bulb thermometers with a single non-contact IR temperature sensor to measure temperature and moisture gradients/fluxes in the first 1-2 m of the surface layer. The materials and tools used cost less than 50 USD total to acquire and operate. The IR technique to obtain the ambient air and wet-bulb temperatures was validated with Kestrel 4000 (discontinued; the Kestrel 5000 replacement typically costs 259 to 319 USD) and Bacharach Sling Psychrometer (typical cost: \(\sim\)85 USD) measurements under various atmospheric conditions, as well as over different surface types to test the versatility of the method. Standard meteorological surface data were collected during each experiment, and moisture parameters were derived via psychometric equations and were further compared to the results obtained with a USAF psychrometric whiz wheel. The IR method described herein was shown to be robust in many environmental settings--both indoors (see Appendix A, trials 54-62) and outdoors--if the IR Thermometer is shaded from direct sunlight, shielded from strong winds (\(>\)5 m s\({}^{-1}\)) and in near equilibrium with its immediate surrounding environment. Moreover, wet-bulb measurements were on average \(-\)0.3 K different from the control Kestrel wet-bulb values. Significantly, when the seven trials with high winds are removed,this average Kestrel wet-bulb to IR wet-bulb difference is reduced to approximately the same average difference as it is when comparing Kestrel to Sling Psychrometer wet-bulb differences (<0.1 K). In general, it took at least two minutes of whirling/spinning the Sling Psychrometer to obtain a steady dry- and wet-bulb set of readings, whereas the IR Thermometer typically steadied in less than 30 s. Finally, the possible utility of using a single IR Thermometer/detector to evaluate moisture and heat fluxes near the surface was explored. Indeed, the case was made suggesting that the IR sensor can be used to sense wet- and dry-bulb temperature changes of 0.7 K and 0.6 K, respectively, over vertical distances as small as 50 cm, thus allowing surface layer temperature and moisture gradients/fluxes to be quantified. The feasibility of this single IR detector method to provide values of surface layer heat and moisture fluxes with reasonable certainty suggests the technique can be exploited with more efficiency and accuracy with a calibrated imaging IR camera or sensor array. Conceptualization, S.F. ; methodology, S.F. ; validation, S.F., L.T. and Y.R. ; formal analysis, S.F., L.T., J.S. and Y.R. ; investigation, L.T and J.M. ; resources, S.F., L.T. and J.M. ; data curation, S.F., J.S. and Y.R. ; writing--original draft preparation, S.F., J.S., Y.R. and K.K. ; writing--review and editing, S.F., J.S., Y.R., K.K. and J.M. ; visualization, L.T., J.S. and Y.R. ; supervision, S.F. ; project administration, S.F. ; funding acquisition, S.F. All authors have read and agreed to the published version of the manuscript. This work was supported by the Joint Directed Energy Transition Office (DE-JTO). Not applicable. All experimental data collected and described in Section 3 can be found in Appendix A. The authors would like to thank the Joint Directed Energy Transition Office for sponsoring this research through the Directed Energy Summer Intern (DESI) program. The views expressed in this paper are those of the authors and do not necessarily reflect the official policy or position of the Air Force, the Department of Defense or the U.S. Government. The authors declare no conflict of interest. The measured and derived experimental data from trials conducted in Dayton OH in June-July 2020 are shown. In addition to the date and time, sky conditions and surface types were documented to explore the versatility and limitations of the IR Thermometer technique.