Some of Recent Developments of HHT

Some of the new developments of HHT have been summarized in a recent review paper on HHT (Huang and Wu 2008) in the Reviews of Geophysics . The related developments that are integrated into our MATLAB program of EMD include:


  1. The confidence limit of EMD (Huang et al. 2003) that provides a measure of the robustness of EMD.  This approach was based on stoppage criteria.  Our results showed that the stoppage criteria could be stable over a wide range of values.


  1. The characteristics of EMD (Flandrin 2004, Wu and Huang 2004) and the statistical test of intrinsic mode function (IMF) (Wu and Huang 2004), which provides a method to determine whether an IMF contains true signals based on statistical comparison with the white nose.  This paper is not only the base for statistical significance test, it is also the foundation for the Ensemble EMD to be discussed below.


  1. The direct quadrature method (DQ) for the calculation of instantaneous frequency (Huang et al. 2008 (link to be added)) that is based on the definition of IMF. This method has been demonstrated to be superior to the traditional instantaneous frequency calculation methods such as Hilbert transformed based method, which is limited by both Bedrosian and Nuttall theorems. 


  1. The Ensemble Empirical Mode Decomposition (EEMD) (Wu and Huang 2005, 2008) that overcomes largely the scale (mode) mixing problem of the original EMD and provides physically unique decompositions, essentially overcome the main drawback of original EMD when it is applied to data with mixed and intermittent scales.


  1. A new definition of adaptive trend and a new detrending method (Wu et al. 2007) based on EMD/EEMD that provide more physically and logically consistent trend as well as detrending.


  1. A new end-point approach and a new sifting stoppage criterion (Wu and Huang 2008) that have some logical and physical justifications.