1. A method for automatically detecting fires on Earth's surface and atmospheric phenomena in Earth's atmosphere by means of a satellite system, the method comprising: acquiring multi-spectral images of the Earth at different times by means of a multi-spectral satellite sensor, each multi-spectral image being a collection of single-spectral images each associated with a respective wavelength (λ), each single-spectral image being made up of pixels each indicative of a spectral radiance (R λ ) from a respective area of the Earth; computing an adaptive predictive model predicting spectral radiances (R PRD,λ ) at a considered time for considered pixels on the basis of previously acquired spectral radiances (R λ ) of the considered pixels and of spectral radiances (R PRD,λ ) previously predicted for the considered pixels by said adaptive predictive model; comparing acquired spectral radiances (R λ ) of the considered pixels at a considered time with spectral radiances (R PRD,λ ) predicted at the same considered time for the considered pixels by the adaptive predictive model; and detecting a fire in areas of the Earth's surface or an atmospheric phenomenon in areas of the Earth's atmosphere corresponding to the considered pixels on the basis of an outcome of the comparison, wherein computing an adaptive predictive model includes: computing, for each considered pixel, a temporal harmonic analysis of the spectral radiances of the pixel related to different times, and acquired at, or predicted for the same wavelength (λ); and computing the adaptive predictive model based on computed low-frequency components of the spectral radiances so as to filter out high-frequency changes in the spectral radiances due to fires on Earth's surface or atmospheric phenomena, wherein computing, for each considered pixel, a temporal harmonic analysis includes: forming a vector (λ) containing the spectral radiances related to different times, and acquired at or predicted for the same wavelength (λ); and computing the temporal harmonic analysis of the vector (h λ ) classifying as valid or invalid acquired spectral radiances (R λ ) according to a given criterion; and wherein forming a vector (h λ ) further comprises: updating the vector (h λ ) with the acquired spectral radiances (R λ ) if they are classified as valid or with the corresponding predicted spectral radiances (R PRD,λ ) if the acquired spectral radiances (R λ ) are classified as invalid.