The Establishment Of Weakly Nonlinear Model For Deep-sea Internal Waves And Its Application In South China Sea

Ocean internal wave is a kind of wave which occurs in the density stratification sea water for thermohaline change. Internal wave has great influence on ocean acoustics, ocean engineering and ocean military affairs etc, so the study of internal wave propagation is of significant importance. In view of data acquisition means, there are mainly four internal wave study methods:field data analysis, laboratory methods, numerical simulation and remote sensing image analysis. But for deep-sea internal waves, data acquisition of field measure and laboratory experiments is more difficult, so appropriate model establishment, numerical simulation as well as remote sensing image analysis methods are used to study deep-sea internal waves in the thesis. The deep-sea internal wave nonlinear Schrodinger(NLS) equation is derived based on two-layer fluid basic equations, and deep-sea internal wave propagation is simulated in South China Sea, then internal wave Synthetic Aperture Radar(SAR) remote sensing detection model is proposed, deep-sea internal wave characteristic parameters in the northern South China Sea are inversed. The thesis are arranged as follows:Firstly, deep-sea internal wave NLS equation is derived. Deep-sea two layer fluid dynamic equations are obtained by introducing speed scalar potential; Under the condition of weakly nonlinearity, the NLS equation for deep-sea internal waves is derived adopting hierarchical method based on the dynamic equations of two-layer fliud; The coefficients of dispersion and nonlinearity are analyzed, and soliton solution of NLS equation is obtained.Secondly, NLS equation is applied in deep-sea internal wave study. The idea of chirps is introduced to study the function of dispersion and nonlinearity. The deep-sea area in the Northern South China Sea is studied, and the environmental parameters are analyzed; Internal wave propagation is simulated using NLS equation in this area, the results show that:internal waves are constantly broadening with their amplitudes gradually decreasing and strong dispersion effect exists; Compared with internal MODIS images, the internal waves evolution simulated is in good agreement with the MODIS images.Finally, deep-sea internal wave SAR detection model is established on the basis of NLS equation. Adopting deep-sea internal wave NLS equation in combination with SAR imaging mechanism, SAR detection model is proposed and the method of deep-sea internal wave parameters inversion is given. Half-width and amplitude of internal waves are obtained respectively from the selected SAR images of internal waves in the northern South China Sea using SAR detection models based on NLS equation and KdV equation, and the comparison with in situ data is made. The results show that the former consists well with the field measurement, while the latter has greater difference with measured data. From the research above, the conclusion can be achieved that NLS model is better than KdV model for deep-sea internal waves study and The rationality of NLS model is verified.