Analysis And Modeling Of The Influence Of Ionosphere On Sea Clutter For Shipborne HF Hybrid Sky-surface Wave Radar

In the shipborne HF hybrid sky-surface wave radar,Electromagnetic waves are reflected by the ionosphere,and the time-varying and unstable ionosphere will have an impact on the signals,making the frequency shift and broadening of sea clutter spectrum after signal processing.At the same time,the change of bistatic angle and the movement of shipborne platform will also cause the sea clutter broadening.All these factors make the echo signal very complicated.In order to solve this problem,this paper mainly studies the influence of the ionosphere on the phase disturbance in the shipborne HF hybrid sky-surface radar.The establishment of the phase disturbance model in the propagation mode makes the influence of the ionosphere on the radio signals more intuitive and clear,and is also conducive to selecting the appropriate method to remove the ionosphere interference according to the phase disturbance model.The main work of this paper can be summarized as follows:Firstly,the structural characteristics of the ionosphere are analyzed.According to the changing characteristics of the ionosphere concentration,the ionosphere is divided into the background ionosphere with slow change and the fast random disturbance ionosphere.Meanwhile,the main background ionospheric electron concentration stratification models are classified and summarized according to their characteristics.The effects of ionosphere on signal and absorption attenuation are analyzed,and the absorption of ionosphere on signal energy is simulated and analyzed.Secondly,the background ionosphere is modeled.The QP/MQP model and analytical ray tracing are used to simulate the ionospheric model with horizontal stratification.For the ionospheric layer with uneven horizontal distribution,QP combined with the mathematical expression to describe the change of horizontal concentration and the numerical ray tracing are used for modeling and simulation.According to the IRI model,three ways of constructing the background ionosphere are put forward,and the advantages and disadvantages of the three methods in accuracy,time and computation are compared and analyzed.Subsequently,the disturbance ionosphere modeling is studied for the spatial and temporal disturbance of the signals in the disturbedionosphere.Analyzed the scintillation caused by the disturbance of ionosphere.The research methods of perturbed ionosphere are summarized and the applicable range of each method is summarized.This paper analyzes the research methods of perturbed ionosphere,and explains the applicable range of each method.Space-time phase perturbationmodeling is carried out for the perturbed ionosphere.The frequency shift and broadening phenomena of ionospheric disturbance are simulated and analyzed.Finally,considering the influence of background ionosphere and disturbance ionosphere,the modeling and simulation of sea clutter are carried out.According to the geometric layout and the generation mechanism of first-order sea clutter,the expressions are derived and the reasons for its broadening are briefly analyzed.Based on the Bragg frequency expression of the first order sea clutter,the signal model of the first order sea clutter,point target and noiseis established.Starting from the space-time perspective of sea clutter,the space-time spectrum model of sea clutter is constructed.Combining with the modeling work of phase disturbance,the influence of ionosphere is added to build the space-time spectrum model of sea clutter.