Abstract
Methods for determining the thermal diffusivity coefficient from a point value of soil temperature of a given thickness based on the results of analyzing the temperature dynamics at one depth based on eight daily observations with an interval of 3 hours have been developed. The proposed methods are based on solving (with two harmonics on the soil surface) inverse problems of the heat transfer equation. Experimental studies on the temperature of the layers (0, 5, 10, 15, 20 and 40 cm) of gley floodplain soil (Calcaric Gleyic Pantofluvic Fluvisol) in the Igdır region (Eastern Turkey) were carried out using Elitech RC-4 sensors during the summer season. Using the obtained data, various methods were used to calculate the thermophysical properties of the soil – thermal conductivity, thermal diffusivity, attenuation depth, heat transfer, and heat flux. Based on statistical criteria, it has been proven that the proposed point model is the best one. It has been established that for the studied soil, the thermal diffusivity is Ƙ = 1.1035 × 10⁻⁶ m²/s, thermal conductivity λ = 1.7612 W/(m °C), damping depth d = 17.42 cm, and thermal effusivity e = 27.9431 Wh0.5/m² °C. In addition, in accordance with the model obtained, it was determined that the largest heat flux on the soil surface occurs at 12:00 pm (q = 106.85 W/m²), and the lowest heat flux occurs at 03:00 am (q = –64.62 W/m²).