Ocean Internal Wave Detection And Parameter Estimation On Spaceborne Interferometric SAR

Ocean internal waves have an important impact on the marine ecological environment,underwater submarine activities,maritime operations and blue ocean economy.With the continuous improvement of Synthetic Aperture Radar ocean remote sensing theory and the rapid development of remote sensing detection technology,it has become one of the important technical means of internal wave observation.At present,there are many researches on the generation mechanism,propagation path,wavelength,amplitude and other hydrodynamic parameters of internal waves,but few researches on the surface current field caused by internal waves.Synthetic aperture radar has the advantages of all-weather and all-weather remote sensing of sea surface.Interferometric SAR technology can obtain dynamic information of sea surface elements(waves,ocean currents,internal waves,etc.).This paper takes the inversion of internal wave parameters as the goal,establishing an internal wave interferometric SAR imaging system,using along-track interferometric SAR to obtain internal waves information and inverting the horizontal internal wave velocity field.The specific research content are as follows:Firstly,the internal wave model excited by the movement of underwater objects is studied,and the influence of the target's different navigation depth and speed on the internal wave height and horizontal velocity is analyzed.The sensitivity of the three wave spectrum models to wind speed is discussed,the sea spectrum model which is the most suitable for real sea surface is selected for random sea surface modeling,and the influence of wind speed and wind direction on the sea surface shape is analyzed.The interaction between internal waves and the sea surface is studied,and internal wave models under different sea conditions are obtained by simulation.Study three sea surface microwave scattering models and the applicable sea surface electromagnetic scattering distribution model is selected based on simulation analysis to calculate the RCS of ocean internal waves.Then,study the process of spaceborne interferometric SAR imaging of internal waves,and the interferometric SAR imaging processing method of internal wave based on dynamic sea echo simulation is designed,and the effectiveness of internal wave imaging is verified by simulation experiments.Furthermore,the influence of different radar parameters,sea surface wind field conditions and underwater target navigation state on internal wave imaging is analyzed,and the conclusion is beneficial to the design of optimal internal wave observation system.Next,the method of obtaining the surface wave flow field of along-track interferometric SAR is studied.The influence of radar parameters(frequency,incident angle,polarization)on interferometric phase measurement is analyzed,and the influence of baseline length on the accuracy and ambiguity of velocity measurement is discussed,which provides a basis for the simulation parameter setting of the interferometric flow measurement system.Based on the results of the internal wave imaging,the interferometric processing research such as image registration,interferometric phase filtering,phase unwrapping(as required)is carried out,and realize the extraction of mixed flow field of sea surface internal waves under simulated low sea conditions and high sea conditions.Finally,study the inversion method of internal wave parameters based on SAR images.Using empirical mode decomposition,complementary ensemble empirical mode decomposition and variational modal decomposition to extract internal waves and estimate the wavelength,compare the three algorithms on the measured image,the estimation results of variational modal decomposition are more accurate.Aiming at the 180° ambiguity in the inversion of the internal wave propagation direction,the wave direction is estimated by combining normalized Radon transform and wavelength estimation.Based on the previously obtained internal wave mixing flow field,the two-dimensional variational modal decomposition algorithm is used to extract the internal wave-induced sea velocity,analyzing simulation experiment and verifying the effectiveness of the internal wave field estimation method.