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Estimating Thermal Diffusivity Near the Soil Surface Using Laplace Transform: Uniform Initial Conditions¹

ABSTRACT

A simplified method based on the numerical integration of the Laplace transform of the one dimensional heat conduction equation in porous media was used to estimate the thermal diffusivity near the surface. The method is based on the analytical solution of the equation of heat conduction and accepts any functional relationship that realistically describes the surface soil temperature as a boundary condition. An optimization scheme was suggested for selecting proper values of Laplace transform parameter s based on maximum duration of the experiment. The method was used to compute thermal diffusivities of two different soil types for a wide range of soil moisture and temperature conditions. Thermal conductivities for each soil were calculated using the computed diffusivities and heat capacities. A comparison of the conductivities estimated with the Laplace transform and the measured values by a transient method showed good agreements between the two methods. A similar comparison between the Laplace transform and the DeVries' model showed significant differences between the two methods.

¹ Contribution no. 82-545-J from the Dep. of Agronomy, Kansas State Univ., Manhattan, KS 66506. This project was supported by NASA Johnson Space Center, Contract NAS 9-16457.

² Research Associate and Agricultural Climatologist, Evapotranspiration Laboratory, Kansas State Univ., Manhattan, KS. 66506.

Received for publication August 31, 1982. Accepted for publication January 10, 1983.