Quantifying surface layer moisture flux from MWIR imagery

Abstract

Psychrometric measurements via sling psychrometers have long been the standard for quantifying thermodynamics of near-surface atmospheric gas-vapor mixtures, specifically moisture parameters. However, these devices are generally only used to measure temperature and humidity at one near-surface level. Multiple self-aspirating psychrometers can be used in a vertical configuration to measure temperature and moisture gradients and fluxes in the first 1-2 meters of the surface layer. This study evaluates the feasibility of a method using infrared (IR) imagery, and a mini-tower of wet and dry paper towels to psychometrically obtain surface layer temperature and moisture gradients and fluxes. First, the possible utility of using a single IR thermometer/detector to evaluate moisture and heat fluxes near the surface was explored, and it was found that the single IR sensor could 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 with reasonable certainty values of surface layer heat and moisture fluxes suggests the technique could be exploited with more efficiency and accuracy with a calibrated imaging IR camera or sensor array. The surface layer dry- and wet-bulb temperatures obtained using an MWIR camera system are compared to Kestrel 4000 Weather Meter and Bacharach sling psychrometer measurements under various atmospheric conditions and surface types to test the viability of the method. Uncertainty statistics are calculated and evaluated to quantify effectiveness.