Modelling the spectrum of the fourier transform of the texture in the solar EIT images

We present a phenomenological parametric model for the spectrum of the discrete Fourier transform (DFT) of the images obtained from the Extreme UV Imaging Telescope (EIT) of the SOHO mission. As this spectrum decays very fast, we model its logarithm rather than the original spectrum. The proposed model is rotation-invariant. The vicinity of the direct current (DC) component of the logarithm of the spectrum is modelled by the sum of two exponential functions, while the region of high frequencies is modelled by a single exponential function summed with a constant. We discuss a method for fitting the model to the experimental data, show the results of numerical experiments, and discuss various measures of goodness of the fit. The fitting of the described model was carried out for a sequence of images covering one year, and the time evolution of the measures of goodness of fit is also presented.