Predicting temperature and heat flow in a sandy soil by electrical modeling

A model based on an electrical analogy between a soil column and an electrical transmission line was developed to predict temperature and heat flow as functions of depth and time in a sandy soil, taking into account changes in soil thermal conductivity and volumetric heat capacity due to variations in water content. The model was excited alternatively by both measured soil temperature at the 1-cm depth and solar radiation [S-r(t)], and solved with available electrical analysis software. The results were compared with field data collected during a 35-d field experiment carried out in the Lido beach, Venice, Italy. A very simple transfer function was identified for using measured S-r(t) as the input signal. This transfer function turned out to vary inversely with S-r(t). When the model is excited by temperature, and soil water content corrected every 5 d, the root mean square error (RMSE) for the calculated temperature at the 5-cm depth is less than 1 degreesC. When it is excited by S-r(t), the RMSE at the 1-cm depth is less than 2 degreesC. Hourly temperatures at different depths were found to depend strongly on surface phenomena, and to a lesser extent on other factors like soil water content below the top layers.