Application of PSD
As mentioned above the PSD is used in wide range of applications. The purpose of its use, is to identify some physical process. This identification is based on the scale invariance that some fields exhibit. The symmetries of the governing equation (see Scale invariance courses) lead in Fourier space to the following expression of the PSD :
Where f represent the frequency and β represent the spectral scaling exponent. The above relation indicate that over the frequency interval considered, the process does not present a characteristic frequency (periodic fluctuations or peak ...). The spectra of the previous shape are characteristic by a cascade process. The best known example of such a result concerns the spectrum of turbulent wind fluctuations ( Kolmogorov, A. N, [1941][1])
