Remote Sensing And Numerical Modeling Of Oceanic Internal Waves

In-situ measurements and remote sensing have showed that internal waves are ubiquitous in the ocean. It is one of the main mechanisms of tidal energy dissipation and ocean mixing. The development of the research of oceanic internal waves would greatly promote the developments of ocean acoustics, ocean sediments, military oceanography etc. It is also very important for the safety of ocean facilities, marine exploitation, and marine traffic and so on. Ocean remote sensing provides much valuable data for the research of oceanic internal waves, which breaks the data shortage from in-situ measurement. However, the remote sensing data cannot be used directly in the research of IWs as in-situ data. Satellite images capture ocean signals from the ocean surface, which cannot provide the vertical profile of oceanic internal waves directly. Therefore, methods must be studied to retrieve oceanic inernal waves from satellite images. So far, almost all the methods to retrieve IWs from satellite images are based on horizontal one-dimensional propagation model, such as Kdv model, which can only extract little information of internal waves. The spatial coverage of a satellite image is more than tens of thousands square kilometers, but the methods so far to retrieve internal wave can only get the information of a certain small area, which is a waste of information. So, methods to retrieve horizontal fully two-dimensional information of internal waves must be developed. To achieve this, the first challenge is to establish a horizontal fully two-dimensional numerical model to simulate the propagation of internal waves. To meet this challenge, the propagation model of internal waves was studied in this paper. A horizontal fully two-dimensional model including the effect of Earth rotation, viscosity and bottom friction is deduced. By this model, the effects of environmental coefficients on the propagation of internal waves are analyzed. Particularly, it is the first time that the role of the horizontal part of Coriolis force played in the propagation of internal waves was studied. According to our research, the vertical part of the Coriolis force was balanced by the pressure gradient of interface, furthermore, the Coriolis force itself has no effect on the propagation speed of internal waves. The horizontal part of the Coriolis force suppressed the nonlinearity of internal waves; and the wavelength was broadened. The number of the fission waves is decreased as well as the wave amplitude by the viscosity effect and bottom friction effect, which leads to the dissipation of wave energy. During the propagation of internal waves, turbulence viscosity cannot be neglected. It plays an important role in suppress the nonlinearity effects of internal waves. The characteristics of the propagation of oceanic internal waves are greatly influenced by bottom topography and water depth. Refraction occurs in the domain of inhomogeneous ocean depth; the shallower the ocean, the obvious the topography effect. When internal wave propagates to the continental shelf, the direction of the IWs is changing perpendicular to the isobath. The numerical model established in this paper can simulate the effect of both environmental coefficients and bottom topography on the propagation of internal waves. Furthermore, this model can be used to simulate the fully two-dimensional propagation of internal waves, such as refraction, reflection etc. The spatial distribution of internal waves in the north-west of South China Sea (SCS) is studied, and the mixing layer depth was retrieved from satellite images. Using the knowledge of polarity conversion of IWs, the accuracy of the retrieved mixing layer depth is evaluated. Most internal waves in the north-west of SCS are coming from the north-east of SCS, propagating westward and north-westward. Both elevation and depression internal waves exist in this sea area, and polarity conversion occurs in certain domain. Based on the dynamical model established in this paper and imaging mechanisms of internal waves, the simulation pro...