Assembly and Evaluation of a Modified Multi-Functional Heat Pulse Probe.
Andrew C. Sherfy, Jaehoon Lee, Stacy Worley, Wesley Wright, and David Smith. Biosystems Engineering and Soil Science, University of Tennessee, 2506 E.J. Chapman Dr., Knoxville, TN 37916
A multi-functional heat pulse probe (MFHPP) has been previously presented and consists of a single central heater, four thermistors, and four electrodes which compose a Wenner array. The MFHPP allows for simultaneous in situ measurements of soil heat capacity, thermal conductivity, thermal diffusivity, volumetric water content, soil water flux density and bulk electrical conductivity. However, previous studies found limitations and manufacturing issues which reduced the measurement resolution and accuracy of the probe. This study will seek to determine the direct sources of measurement error which will in turn allow for possible refinements to probe construction and post data analysis. These will include methods to reduce errors stemming from probe construction, specifically variations in radial distance of the four thermistors as well as maximizing the heat flux to the soil. Currently, we believe a partial solution to the problem is in the construction and design process through the use of precision cut electronic boards to minimize sensor spacing variation and a precision timing and current circuit for the probe heater which will accurately quantify the amount of heat applied directly to the soil. Another objective is to improve post data analysis. Sensitivity analysis will be performed to better understand the importance of each parameter used; such knowledge can be used for choosing proper independent determination of the parameters and analytical and numerical techniques. The study might involve fractal modeling of the probe-soil system.