Premium
Soil Heat Storage Measurements in Energy Balance Studies
Author(s) -
Ochsner Tyson E.,
Sauer Thomas J.,
Horton Robert
Publication year - 2007
Publication title -
agronomy journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.752
H-Index - 131
eISSN - 1435-0645
pISSN - 0002-1962
DOI - 10.2134/agronj2005.0103s
Subject(s) - heat flux , energy balance , soil science , water content , volumetric heat capacity , thermal energy storage , flux (metallurgy) , heat transfer , sensible heat , environmental science , soil water , chemistry , thermodynamics , physics , geotechnical engineering , geology , organic chemistry
Energy balance studies require knowledge of the heat flux at the soil surface. This flux is determined by summing the heat flux at a reference depth ( z r ) some centimeters below the surface and the rate of change of heat storage in the soil above z r . The rate of change of heat storage, or heat storage for short (Δ S ), is calculated from soil volumetric heat capacity ( C ) and temperature. The objectives of this study were to determine how choices regarding z r , C measurements, and Δ S calculations all affect the accuracy of Δ S data. Heat transfer theory and data from three field sites were used toward these ends. In some studies, shallow reference depths have been used and Δ S neglected. Our results indicate that when z r is sufficiently deep to permit accurate heat flux measurements, Δ S is too large to neglect. Three methods for determining C were evaluated: soil sampling, the ThetaProbe soil moisture sensor, and heat pulse sensors. When C was determined using all three methods simultaneously, the estimates agreed to within 6% on average; however, the temporal variability of C was best recorded with the automated heat pulse sensors. Three approaches for calculating Δ S were also tested. The common approach of letting C vary in time but neglecting its time derivative caused errors when soil water content was changing. These errors exceeded 200 W m −2 in some cases. The simple approach of assuming a constant C performed similarly. We introduce a third approach that accounts for the time derivative of C and yields the most accurate Δ S data.