An Empirical Method of Estimating Soil Thermal Inertia

Abstract

A method of estimating soil thermal inertia (STI), which uses midday soil heat flux (Gm) and diurnal surface temperature amplitude as the inputs, is presented in the paper.Gmis achieved from an empirical relationship between net radiation (Rn) and soil heat flux (G). To validate the STI method, a method proposed by Verhoef, which requires STI and a Fourier series analysis on surface temperature, is used to estimate diurnalG. By comparing diurnalGestimates and diurnalGmeasurements, the STI method is evaluated indirectly. The results show that the diurnal curve ofGestimates can coincide with that ofGmeasurements for bare soil, with the correlation coefficient (R2) of 0.64, bias of 10.1 W·m−2, and root mean squared errors (RMSE) of 40.9 W·m−2. For the vegetated surface,R2is 0.56, bias is −11.9 W·m−2, and RMSE is 49.2 W·m−2. The large uncertainty in the estimation ofGmresulting from the wider variation of the empirical relationship between Rn andGand the difference between mixed surface temperature and soil surface temperature may be the two primary factors for the larger deviation of the diurnal shape and the magnitude betweenGestimates andGmeasurements for the vegetated surface.