W. Iqbal, M. . Shoaib, J. . Ahmad, M. A. . Butt, A. . Khalid, and M. Adnan, “Parametric and Non-Parametric Spectral Signal Processing Techniques for Estimation of Periodicity in Sunspot Numbers: Spectral signal processing techniques for estimation of preiodcity in sun spot numbers”, PPASA, vol. 56, no. 1, pp. 9–20, Mar. 2021.