Abstract
An empirical calibration method for temperature dependence of a commercially available capacitance probe (ECH2O probe : Decagon Devices) was presented in this paper. A laboratory experiment was conducted to obtain probe outputs at different water contents (θ) and temperatures (T) using soil from Shaanxi Province, located in the Loess Plateau, China. The probe output showed strong positive response to T. A calibration equation describing the probe output as a function of θ and T was developed through an empirical curve fitting approach. The θ values were estimated by solving the calibration equation numerically. The root mean square errors between actual and estimated θ were 0.016 m3 m-3. We also discussed the theoretical background of the temperature dependence of the probe using the results from the experiment. The calibration equation was applied to field observation data in the Loess plateau. The equation significantly reduced the daily and seasonal fluctuations of the probe outputs to T. A linear calibration equation provided by the manufacturer, which neglects temperature dependence, caused incorrect interpretation of water movements, suggesting the importance for temperature calibration in arid environments.
