5Huang N E, Shen Z, Long S R. The empirical mode decomposition and the Hilbert spectrum for nonlinear and non2stationary time series analysis[J]. Proc. R. Soc. Lond. A, 1998,454:903-995.
6Daniel J Y, Matthias G I, John E F, et al. Analysis and application of coal-seam seismic waves for detecting abandoned mines [J]. Geophysics, 2007, 72(5):7-15.
