APPLICATION OF HHT IN TIME SERIES ANALYSIS FOR IGSFIDUCIAL STATIONS
1)School of Geodesy and Geomatics,Wuhan University,Wuhan 430079
2)Chinese Academy of Surveying and Mapping, Beijing 100830
3)Satellite Surveying and Mapping Application Center, NASMG, Beijing 100830
Abstract Taking the GPS fiducial stations, BJFS and BJSH as the examples, the time series in elevation direction from 2000 to 2006 were decomposed into a finite number of intrinsic mode function，whose frequency was decreasing, and the residual representing the trend of the time series. The linear rates of the two stations were -0.533 mm/a, -2.083 mm/a respectively. Furthermore every component is transformed with Hilbert algorithm, though the procedure twodimensional marginal spectrum and three-dimensional Hilbert spectrum in time-frequency-energy space were obtained and analyzed. The marginal spectrum has perfect timefrequency concentration; and then the frequency of high amplitudes is no more than 3 cycle/a. The main components in time series of the both stations are a secular nonlinear trend，and semiannual signals, and annual signals which is obvious and about 351 days. Moreover, Hilbert spectrum has high resolution and the ability of outlier detection. Afterwards the time series was processed by EMD lowpass filtering and the result is compared to that of sym6, db8 wavelet. De-noising results by EMD was much superior, slick and no glitch, which indicates that this method is more efficient in eliminating instantaneous strong noise
