|Horton, Robert - IOWA STATE UNIV|
Submitted to: ASA-CSSA-SSSA Annual Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: July 26, 2004
Publication Date: November 1, 2004
Citation: Ochsner, T.E., Sauer, T.J., Horton, R. 2004. Measurement of near-surface soil heat storage in energy balance studies [CD-ROM]. ASA-CSSA-SSSA Annual Meeting Abstracts, November 1-4, 2004. Technical Abstract: In energy balance studies, the rate of change of soil heat storage (S) and an estimate of the reference soil heat flux (Gr) at some depth are typically used to determine the surface flux (G0). Soil volumetric heat capacity (C) must be determined to calculate S. Our objective is to quantify the effects of the method of C determination on S. At three field sites, we compared determination of C by soil sampling every 2-3 days, by Theta Probe water content measurements every 2-3 days, and by hourly measurements using heat pulse sensors (HPS). When C was determined using all three techniques simultaneously, the estimates agreed to within 6% on average. However, sampling three times per week was not frequent enough to consistently record the temporal variations in C. With sampling intervals of 2-3 days, the rate of change of C with respect to time is unknown and neglected. This introduced errors occasionally exceeding 200 W m-2 during infiltration and persistent but smaller errors during soil drying. Hourly measurements using HPS avoided these errors. We recommend that automated techniques, such as the HPS, be used in long-term energy balance studies for frequent determination of C. We also recommend that S be measured in all energy balance studies. Neglecting S introduces unnecessary and relatively large errors in G0.