Improved Fourier modelling of soil temperature using the fast Fourier transform algorithm

In the general case, the temperature field and the heat flow of soils are controlled by two coupled first-order differential equations with the boundary condition defined by the heat flow through the surface boundary due to the net radiation and the sensible and latent heat flows between the surface and the atmosphere. Periodic diurnal temperature variations have earlier been studied using Fourier modelling techniques. In this paper, it is shown how this method can be extended to non-periodic diurnal temperature variations due to changing weather conditions. The calculations can be speeded up significantly using FFT-processing. Furthermore, the algorithms are generalized to multiple soil-layers.