UNCERTAINTIES OF APPARENT THERMAL DIFFUSIVITY OF ALLUVIAL-MEADOW SOIL ESTIMATED BY DIFFERENT NUMERIC METHODS

Milena Kercheva, Katerina Doneva

Abstract: The apparent thermal diffusivity (a) of Fluvisol was estimated by applying the Amplitude, Phase, Arctangent, Logarithmic and Harmonic methods on soil temperature data measured at 0.10 and 0.20 m depth with automatic meteorological station in 92 clear sky days under different soil moisture conditions. The uncertainty between these method was high (Cv = 31% in average). Our results showed that there was not significant difference between the apparent thermal diffusivity obtained by the Amplitude, Logarithmic and Harmonic methods. The Phase and Arctangent methods produced higher values of the apparent thermal diffusivity and with a higher coeffi cient of variation. The lowest variation of a was obtained by the Harmonic method (Cv = 15%), which can be recommended for estimation of thermal diffusivity on a daily basis. The obtained results were compared with direct measurement in laboratory conditions with KD2-Pro device, and with estimation by de Vries model (de Vries, 1963), and by the annual soil temperature wave method based on 10 years records (Marinova et al., 1990). The minimum values of a obtained on a daily basis coincided with the highest values predicted by de Vries model for high soil moisture content. It was not found dependence of the apparent thermal diffusivity from soil moisture content. The prediction of a by the annual soil temperature wave method was close to the average values obtained on a daily basis. This study demonstrate the possibility
of using soil temperature data registered by automatic weather station to produce reliable estimates of soil thermal diffusivity for relatively shorter time period.

Keywords: numeric methods; soil thermal diffusivity; thermal properties

Date published: 2017-07-07