EN
Introduction to the Hilbert-Huang transform. The Hilbert-Huang transform (HHT) is an empirically based data-analysis method. Its basis of expansion is adaptive, so that it can produce physically meaningful representations of data from nonlinear and non-stationary processes. The advantage of being adaptive has a price: the difficulty of laying a firm theoretical foundation. This paper is an introduction to the basic method, which is followed by brief descriptions of the recent developments relating to the normalized Hilbert transform, a confidence limit for the Hilbert spectrum, and a statistical significance test for the intrinsic mode function (IMF). These problems include the general method of adaptive data-analysis, the identification methods of nonlinear systems, the prediction problems in nonstationary processes, which is intimately related to the end effects in the empirical mode decomposition (EMD), the spline problems, which center on finding the best spline implementation for the HHT, the convergence of EMD, and two-dimensional EMD, the optimization problem or the best IMF selection and the uniqueness of the EMD decomposition.