Improved Soil Heat Flux Assessment Using a Penta-Needle Heat Pulse Probe.

Soil transport processes including hydraulic and thermal fluxes are fundamental to hydrology, ecology and agriculture. Soil heat flux estimates are challenging measurements due to highly dynamic moisture redistribution processes close to the soil surface. Measurements are generally conducted with soil heat flux plates, which, because of their installation depth, are relatively insensitive to near-surface heat flux. We evaluated a novel array of penta-needle heat pulse probes (PHPP) as an alternative method for multi-layer heat flux measurements. Each penta-needle heat pulse probe is capable of measuring soil temperature and thermal properties (conductivity and diffusivity) as well as providing calculated heat capacity and volumetric water content estimates for each depth increment. These measurements and calculated properties facilitate estimation of soil heat flux and sensible heat storage. We evaluated a 3-PHPP array in a sand column where two different brands of soil heat flux plates were installed for comparison. Applications for the PHPP array include weather stations, eddy covariance stations and other subsurface soil monitoring needs.