A New Low-Cost Sensor for Determining Heat and Moisture Fluxes

Eddy covariance measurements from micrometeorological towers have long been used to determine heat and moisture fluxes. Installing and maintaining high-quality eddy covariance measurements, however, is costly monetarily and is labor intensive. In the present study, we evaluated a UPSI F-TUTN fast-response temperature and humidity sensor, which is a new, low cost sensor that may be used to help derive fluxes of latent and sensible heat once knowledge of the sensor’s performance is achieved. To this end, we installed the sensor inside a Thunder Scientific 2500 two-pressure humidity generator and compared the sensor’s measurements with those from a Vaisala HMT330 temperature and relative humidity sensor. We further assessed the performance of the fast-response sensor over a nine-day period near Oak Ridge, TN in June 2017 by comparing mean and turbulent quantities with those obtained from an EC155 CO₂ and H₂O Closed-Path Gas Analyzer and RM Young sonic anemometer. The fast-response sensor showed a consistent bias when compared with the EC155; water vapor mixing ratios from the fast-response sensor were typically 6 mmol mol^-1 larger than those from the EC155. We corrected the bias using a linear transfer function and applied the correction to the 10 Hz water vapor measurements to compute 30 min covariances. Additional testing is underway to further evaluate the sensor and will also be presented. The evaluations conducted so far, however, are encouraging and indicate that the fast-response sensor may be reliably used for applications requiring low cost, low weight, yet high quality flux measurements, e.g. small unmanned aircraft systems (sUAS) for deriving horizontal and vertical variations in heat and moisture flux.