| Marine atmospheric duct has a strong temporal and spatial distribution, according to the statistics of Patterson, the average appearance probability of surface duct on the world scale is 15% which varies greatly in different regions, and the probability of evaporation duct is much higher than surface duct. By using the spatial and temporal distribution parameters of atmospheric duct in sea battlefield, it can significantly improve the actual performance of ship-borne radar remote detection and upgrade the long-range strike capability of vessels, it has a great significance for warship fight aided decision-making.The large-scale atmospheric duct parameters are difficult to continuously obtain by using conventional means. It is a rapidly developed new technology for using radar sea clutter to inverse atmospheric duct parameters in recent years, the technology can be used for real-time and continuously inversing atmospheric duct parameters from sea clutter power information and diagnosing whether atmospheric duct is existing in the current sea area or not. If it exists, then the height of atmospheric duct, intensity, thickness and other parameters can be further inversed, and the distribution of these parameters with the radar action distance.First, this article describes the types of atmospheric refraction and the conditions, the reasons, the classification and the impact of atmospheric duct on the propagation of radar wave. Then, we introduce three kinds of electromagnetic wave propagation model theories:The electromagnetic propagation losses under the standard atmosphere environment and the evaporation duct environment are simulated by using ray tracing technology, which points out that the simulation process can basically determine the propagation path of electromagnetic waves and preliminarily ascertain whether atmospheric duct propagation occurs in the marine atmosphere or not and the positions. The principle of parabolic equation is recommended, the initial field and boundary conditions problems are discussed, and the numerical solution of parabolic equation is given by using the split-step Fourier transformation method. The electromagnetic propagation loss model in the marine atmospheric environment is shown, and changes of one-way electromagnetic propagation loss with distance and height are calculated by using it. Introduce the duct modal theory and points out the advantages and disadvantages of the theory. At last, we discuss the inversion method of marine atmospheric duct parameters and provide the flow chart of Particle Swarm Optimization. The five-parameter atmospheric duct model is introduced, the objective function is constructed by using the discrete clutter power data in the direction of 135 degrees in radar images and the theoretical calculation of sea clutter by using parabolic equation model. The atmospheric duct parameters of the five-parameter model are inversed by combining with the Particle Swarm Optimization algorithm and the test collected sea clutter data and the radiosonde data. As an important component of the atmospheric duct, evaporation duct is a unique form of duct in marine atmosphere. Evaporation duct height is one of the important parameters of evaporation duct which can characterize the duct intensity and can determine the evaporation duct effects on electronic equipment. The inversion of evaporation duct height is 13.4m, while the theoretical height is 12.5m, the relative error is 7.2%, it can be seen that the inversion results compare well with the measured values which can reflect the change of atmospheric refractive index profile with height above the sea surface. Analysis shows that there are many reasons contributed to these errors, such as test venues selection, the impact of the offshore nonlinear heterogeneity factors, etc. Believe that through strengthening the ship-based test and collecting more abundant test data, the very satisfactory results can be obtained.In short, this thesis implements atmospheric duct parameters inversion by using Particle Swarm Optimization algorithm which proves the scientific nature and feasibility of its, provides the algorithm basis to further develop detection equipments which can adapt to many radars and inverse a wide range of atmospheric duct parameters. Marine atmospheric duct has a strong temporal and spatial distribution, according to the statistics of Patterson, the average appearance probability of surface duct on the world scale is 15% which varies greatly in different regions, and the probability of evaporation duct is much higher than surface duct. By using the spatial and temporal distribution parameters of atmospheric duct in sea battlefield, it can significantly improve the actual performance of ship-borne radar remote detection and upgrade the long-range strike capability of vessels, it has a great significance for warship fight aided decision-making.The large-scale atmospheric duct parameters are difficult to continuously obtain by using conventional means. It is a rapidly developed new technology for using radar sea clutter to inverse atmospheric duct parameters in recent years, the technology can be used for real-time and continuously inversing atmospheric duct parameters from sea clutter power information and diagnosing whether atmospheric duct is existing in the current sea area or not. If it exists, then the height of atmospheric duct, intensity, thickness and other parameters can be further inversed, and the distribution of these parameters with the radar action distance.First, this article describes the types of atmospheric refraction and the conditions, the reasons, the classification and the impact of atmospheric duct on the propagation of radar wave. Then, we introduce three kinds of electromagnetic wave propagation model theories:The electromagnetic propagation losses under the standard atmosphere environment and the evaporation duct environment are simulated by using ray tracing technology, which points out that the simulation process can basically determine the propagation path of electromagnetic waves and preliminarily ascertain whether atmospheric duct propagation occurs in the marine atmosphere or not and the positions. The principle of parabolic equation is recommended, the initial field and boundary conditions problems are discussed, and the numerical solution of parabolic equation is given by using the split-step Fourier transformation method. The electromagnetic propagation loss model in the marine atmospheric environment is shown, and changes of one-way electromagnetic propagation loss with distance and height are calculated by using it. Introduce the duct modal theory and points out the advantages and disadvantages of the theory. At last, we discuss the inversion method of marine atmospheric duct parameters and provide the flow chart of Particle Swarm Optimization. The five-parameter atmospheric duct model is introduced, the objective function is constructed by using the discrete clutter power data in the direction of 135 degrees in radar images and the theoretical calculation of sea clutter by using parabolic equation model. The atmospheric duct parameters of the five-parameter model are inversed by combining with the Particle Swarm Optimization algorithm and the test collected sea clutter data and the radiosonde data. As an important component of the atmospheric duct, evaporation duct is a unique form of duct in marine atmosphere. Evaporation duct height is one of the important parameters of evaporation duct which can characterize the duct intensity and can determine the evaporation duct effects on electronic equipment. The inversion of evaporation duct height is 13.4m, while the theoretical height is 12.5m, the relative error is 7.2%, it can be seen that the inversion results compare well with the measured values which can reflect the change of atmospheric refractive index profile with height above the sea surface. Analysis shows that there are many reasons contributed to these errors, such as test venues selection., the impact of the offshore nonlinear heterogeneity factors, etc. Believe that through strengthening the ship-based test and collecting more abundant test data, the very satisfactory results can be obtained.In short, this thesis implements atmospheric duct parameters inversion by using Particle Swarm Optimization algorithm which proves the scientific nature and feasibility of its, provides the algorithm basis to further develop detection equipments which can adapt to many radars and inverse a wide range of atmospheric duct parameters. |
PDF Full Text Request