Internal waves include soliton of period 10-20 minutes and tidal frequency waves. Large internal solitons with amplitude over 100 m were observed frequently in the South China Sea (SCS). There were convergence zones of 500-1000 m wide in the wave front of solitons which can be detected by satellite from the space. The hypothesis of this study is the internal wave signal can be extracted from the sea surface anomalies of satellite altimetry. Data analyzed include TOPEX/Poseidon altimeter from August 2002 to October 2005 in the northern SCS and Kuroshio regions. Methods applied include (1) standard deviation analysis, (2) harmonic analysis and (3) wavenumber spectrum analysis. The results show that¡]1¡^there is an annual variation in the sea surface height, which is explained due to water temperature changes in different seasons. (2) The results of harmonic analysis show that the amplitude of M2 aliasing is only a few centimeters on the sea surface. The different is small between internal active region and that of without. (3) The absolute values of slope, of internal wave energy and wavenumber spectrum, are 2-3 in the wave active region. This suggests that there are wave motions of scale 100 km or larger, which matches with the length scale of internal waves in the northern SCS.

In the traditional analysis of acoustic wave propagation in an ocean waveguide, it's generally assumed that acoustic properties, including density and sound speed profile at seabed are taken to be constant. However, recent experimental data provided by Hamilton~(1980)~ have shown that the sediment layer in the seabed experiences a transitional change in which the density and the sound speed vary continuously from one value at the top to another at the bottom of the layer. The objective of this study is to investigate the surface-generated ambient noise in an isovelocity waveguide with a non-homogeneous fluid sediment layer. The noise model was first proposed by Kuperman and Ingenito~(1980) in the study of surface-generated ambient noise using normal mode approach, and the model proposed by Robins (1993) in the study of the sediment layer change in which the density and the sound speed vary continuously. It is demonstrated that the noise intensity may be affected by the stratification mainly through the continuous spectrum, in that the continuous spectrum is equally important as the normal modes in the present analysis. The continuous variation of the sediment layer reduces the contrast of the interface, which in turn affects the wavenumber spectrum, particularly in the continuous spectrum region. The results show that the horizontal correlation length of the noise field increases as that of the noise random sourse increase, but the vertical correlation length of the noise field decreases as that of the noise random sourse increase.