An Empirical Method of Estimating Soil Thermal Inertia

Abstract EN

A method of estimating soil thermal inertia (STI), which uses midday soil heat flux ( G m ) and diurnal surface temperature amplitude as the inputs, is presented in the paper.

G m is 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 diurnal G .

By comparing diurnal G estimates and diurnal G measurements, the STI method is evaluated indirectly.

The results show that the diurnal curve of G estimates can coincide with that of G measurements for bare soil, with the correlation coefficient ( R 2 ) 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, R 2 is 0.56, bias is −11.9 W·m−2, and RMSE is 49.2 W·m−2.

The large uncertainty in the estimation of G m resulting from the wider variation of the empirical relationship between Rn and G and 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 between G estimates and G measurements for the vegetated surface.