The Modeling Of Evaporation Duct And Investigation Of Microwave Propagation Characteristics

The evaporation duct has significant effects on electromagnetic wave propagation above the ocean.As a result,timely and accurate assessments of evaporation ducts and their impacts on electromagnetic wave propagation are very important for ship borne electromagnetic system design and application.Meanwhile,the communication range above the ocean can be extended by utilizing evaporation duct.However,the current methods of monitoring and forecasting evaporation duct are not accurate.The spatial resolution of these methods are low and the decision aid methods of communication utilizing evaporation duct are lacked.Thus,this thesis does a comprehensive research on hind cast,now cast and forecast methods of evaporation duct by using the up-to-date reanalysis product,marine boundary layer experiment results and mesoscale forecast model.By using these methods,the reanalysis,now-cast and forecast of evaporation duct for large sea areas can be realized.The electromagnetic wave propagation in evaporation duct can also be analyzed.There are three parts of research contents in this these: the monitoring,modeling and forecasting of evaporation duct;microwave propagation characteristics;and the decision aids methods of communication utilizing evaporation duct.These methods are all verified by both the computer simulation and experiment at sea and the decision aids method are verified by the experiment at sea using the communication systems.The works of this thesis are summarized as follows:1.The evaporation duct model is improved in the stable condition by using the stability function measured in the recent marine boundary layer experiment.The improved model are more accurate in the stable condition.Meanwhile,based on the improved evaporation duct model,the impacts of atmospheric factors(sea surface temperature,air temperature,pressure,wind speed and relative humidity)on evaporation duct height are investigated.2.The new evaporation duct climatology are studied based on the up-to-date reanalysis product and the improved evaporation duct model.The buoy data and the microwave path loss data are used to verify the climatology.The spatial and temporal distributions of the evaporation duct in the South China Sea and all over the world are obtained based on the new climatology.This new climatology provides better evaporation duct data,at a higher resolution of 0.312°×0.313°.3.The evaporation duct real time monitoring method is proposed based on the improved evaporation duct model.The method is used to sense the evaporation duct environment along the ship's cruise.The reliability of the shipboard observation is analyzed based on the experiment in the South China Sea in 2012.The sensitivity of evaporation duct model is analyzed and the sugguestion of sensor selection and installation are given.The short term forecast method of evaporation duct are proposed utilizing the GFS products and the WRF mesoscale prediction model.The spatial resolution are improved by using multi-scale nested method.The accuracy of this method is also improved by selecting the appropriate parameterization scheme.4.The influences of horizontal inhomogeneity and the obstacles on microwave propagation in evaporation duct are studied by the parabolic equation model and ray optics model.The relevant experiments were held in the South China Sea to verify the conclusion.The frequency response of evaporation duct channel is investigated both from numerical simulation and experiment verification.It is shown that the frequency response of evaporation duct channel is similar to that of the high pass filter.The relevant conclusions are important for the ship borne electromagnetic system designs and applications.5.The decision aid methods for the communication systems utilizing evaporation duct are investigated.The communication range,bandwidth,optimal frequency and optimal antenna height can be obtained by the decision aid method.The proposed method are verified by the experiments at sea using real communication systems.The communication probability of communication systems utilizing evaporation duct are investigated based on the evaporation duct climatology.The communication probability is calculated in the typical sea area and are significant for the ship borne communication systems design and applications.