Improved Analysis of Heat Pulse Signals for Soil Water Flux Determination

Soil water flux (J) can be estimated from the velocity (V) of a pulse of heat introduced into the soil. Here we consider a method in which V is measured with a three-probe sensor. The center probe heats the soil, and the outer probes measure temperature increases downstream (T(d)) and upstream (T(u)) from the heater. An equation was recently proposed for approximating J from the ratio T(d)/T(u). In this note we show that the accuracy of this equation can be improved by adding a term to correct for the time dependence of T(d)/T(u). This term is simple to evaluate and requires no additional measurements. Example calculations (three cases) are used to evaluate improvement in accuracy. When T(d)/T(u) is measured at a time of 45 s, relative errors in flux estimates are reduced from 10.5, 2.6, and -10.5% to 0.23, 0.06, and -0.23%, respectively, by using the correction term.