Influência do posicionamento de sondas térmicas na determinaçao da difusividade térmica e do fluxo de calor do solo em condiçoes de campo

Thermal diffusivity of a floodplain soil without vegetation, located at Coxixola, State of Paraiba, Brazil, was determined under field conditions. Temperature evolution at several soil depths under different moisture conditions was measured from February to October 1995. The influence of distance (Δz) between thermal sensors on the diffusivity values was evaluated. Δz was calculated by the following methods: amplitude, phase, logarithmic, arctangent, and harmonic methods. The values obtained by the harmonic method for Δz = 11.0 cm were 13% and 100% higher than those for Δz = 2.5 cm under moist and dry conditions, respectively. For positioning errors of±1 cm, the relative variation in the diffusivity values for Δz = 2.5 cm was -66% and +101%, respectively, and -17% to +19% for Δz = 11.0 cm. In addition to the identification of significant discrepancies between the values obtained by the different methods, it was also found that values of thermal diffusivity and, therefore heat flux on the soil surface, may be significantly affected by positioning errors of the thermal sensors.