Sequence of the spectral parameters β_i = [β_i, s, β_i, d] used in our experiments and derived from the maximization of the spectral likelihood, Eq. (16). The panels in clockwise order show consecutive zooms on the sequence that converged on the likelihood peak values of β = [− 3.006, 1.584], slightly off the true values marked by the blue solid point in the top left panel and given by Eq. (45) (with T_d fixed in our test cases). The sequence was generated as described at the end of Sect. 4.1.2.