A Fourier Spectral Method to Measure the Thermal Diffusivity of Soil

Abstract

It is well established that amplitude decays and phase shifts as a function of depth, frequency, and thermal diffusivity when a periodic surface temperature signal conducts into the ground. In historical practice, this principle has often been employed to estimate soil thermal diffusivity using observations of the dominant diurnal and annual temperature signals. We describe and demonstrate a method to infer thermal diffusivity over a broad bandwidth in the frequency domain using high fidelity time-series ground temperature records. We draw information from thermal signals generated by meteorological events over weeks and months, as well as the dominant diurnal signal. Both the decay in ampli..