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United States Department of Agriculture

Agricultural Research Service

Title: Improved Analysis of Heat Pulse Signals for Soil Water Flux Determination

Authors
item Kluitenberg, Gerard - KANSAS STATE UNIV
item Ochsner, Tyson
item Horton, Robert - IOWA STATE UNIV

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 23, 2006
Publication Date: January 1, 2007
Citation: Kluitenberg, G.F., Ochsner, T.E., Horton, R. 2007. Improved analysis of heat pulse signals for soil water flux determination. Soil Science Society of America Journal. 71:53-55.

Interpretive Summary: The rate of water flow in soil is difficult to measure accurately. One approach being explored by scientists is the heat pulse ratio method which uses a three-probe sensor. The center probe is used to heat the soil, and the outer probes measure changes in temperature downstream (Td) and upstream (Tu) from the heater. An equation was recently proposed for calculating the soil water flow rate from the ratio Td / Tu. We found an improved equation that includes a term to correct for the time dependence of Td / Tu. This term is simple to evaluate, requires no additional measurements, and can improve the accuracy by 10%. This new equation will help scientists obtain more accurate measurements of soil water flow when using the heat pulse ratio method.

Technical Abstract: Soil water flux (J) can be estimated by measuring 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 is used to heat the soil, and the outer probes measure changes in temperature downstream (Td) and upstream (Tu) from the heater. An equation was recently proposed for approximating J from the ratio Td / Tu. 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 Td / Tu. This term is simple to evaluate and requires no additional measurements. Example calculations (three cases) are used to evaluate improvement in accuracy. 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. Calculations using published data show similar improvements in accuracy.

Last Modified: 12/28/2014