Improved Fourier modeling of soil temperature using FFT algorithms

In general, the temperature field and the heat flow of bare soils are controlled by two coupled, first-order differential equations, with the boundary condition defined by the heat flow through the surface due to net radiation and the sensible and latent heat exchange between the soil and the atmosphere. Periodic diurnal temperature variations have previously been studied using Fourier modeling techniques. In this paper, it is shown how this method can be extended to nonperiodic diurnal temperature variations and heat flows due to changing weather conditions. The time interval covered can be selected from hours up to weeks or years. The calculations are speeded significantly using fast Fourier transform (FFT) processing. The algorithms are generalized to multiple soil layers as well.