The Research And Application Of Signal Analysis Based On HHT And Its Improved Method

In recent years, Hilbert Huang Transform is a new method developed for analysis of non-stationary signal, unlike FFT using predetermined basis functions, the core of HHT is empirical mode decomposition (EMD)through which we can gain a group of their own intrinsic mode function (IMF), then by transforming the IMFs we can construct the Hilbert spectrum. Although HHT is adaptive, multi-resolution and has other unique advantages, it is very suitable for analyzing non-linear, non-stationary signal, but it also some disadvantages.Marine magnetotelluric method is similar to magnetotelluric method, because of the particularity of the ocean environment, marine magnetotelluric signal is not only weak, susceptible to noise interference, but also because of the movement of the water, complex ocean background, its SNR is low, here we analog a signal on the basis of characteristics of marine MT signal, and its time-frequency concentration and resolution of short-time Fourier transform, the Winger-Ville distribution, Choi-Williams distribution, wavelet transform and HHT is compared, it is proved that HHT has better adaptive and higher resolution, it can be very good at handling the marine magnetotelluric signals.Then this paper discusses the mode mixing problem existing in EMD algorithm which has serious impact on signal analysis results and presents the improved method-ensemble empirical mode decomposition (EEMD), by adding white noise in the signal then as a whole being decomposed, the different scale signals can be collated in the proper IMFs, using white noise with zero mean value properties, the white noise to the signal influence is eliminated, we can see EEMD can solve mode mixing problemhas better by marine MT signal simulation.At last marine MT simulation signal was reconstructed by EMD and EEMD through Hlibert spectrum and marginal spectrum results we can know, although the EMD denoising can suppress many noise, but due to mode mixing problem, low-frequency signal chaos, the EEMD denoising, not only eliminates the most noise, but also eliminates low frequency confusion caused by he mode mixing, and leads to fewer low frequency harmonic and reappears the marine magnetotelluric signal characteristics more clearly.