Research On Ionosphere Decontamination And Maneuvering Target Detection In Skywave OTH Radar

Skywave Over-The-Horizon(OTH)radar launches high frequency electromagnetic wave into the air and receives the reflected echo from the ionospheric for target detection.OTH radar has characteristics such as the far detection distance,the high cost-effectiveness,and the ‘Four resist ability'.OTH radar has been widely applied in the field of strategic warning,drug smuggling,air-sea traffic management,environmental remote sensing,nuclear explosion monitoring,etc.OTH radar has many advantages at the same time many problems and challenges.First,because its working mechanism is ionospheric reflection,the echo signal is polluted by ionospheric phase contamination,which makes the strong sea clutter spectrum broadening thus brings difficulties to ship target detection.Moreover,the maneuverability of target leads its Doppler spectrum spread,and the long coherent accumulation time of OTH radar increases the degree,which is unfavorable for the estimation of target parameters.In addition,no prior error information about ionosphere is considered,and the errors of ionospheric sounding equipment are ignored when the target parameters are calculated in skywave OTH radar,which makes the estimated parameters not accurate enough.Based on the above problems,this paper has carried on the thorough research,the main work is as follows:(1)Ionospheric decontamination algorithm based on Maximum-Likelihood method.A ionospheric phase decontamination algorithm in OTH radar is proposed based on the Maximum-Likelihood(ML)method.In this algorithm,the Bragg peak is modeled as a phase polynomial,and estimation of the perturbation phase is achieved by maximizing the likelihood function.To avoid matrix inversion in the ML method,the ML issue is further transformed to a least-squares issue in this algorithm.The coefficients of phase are solved by the genetic algorithm.The results of this experiment show that this algorithm is better than the existing algorithms.(2)Maneuvering target detection algorithm based on Hankel matrix decompositionA maneuvering target detection algorithm is proposed based on Hankel matrix decomposition.In this algorithm,the estimation of target parameters is transformed into the convex optimization problem based on linear principal component analysis(PCA).The echo signal is constructed as a Hankel matrix which is decomposed into a Low-Rank matrix plus sparse matrix.Then the time-frequency distribution of the matrices are solved to realize the simultaneous detection of multiple targets.The simulation results show that the proposed algorithm has higher accuracy than the existing algorithms.(3)Joint estimation algorithm of target and ionospheric parametersA joint estimation algorithm of target and ionospheric parameters in OTH radar is proposed.In this algorithm,the priori error information about ionospheric sounding equipment is taken into account.The parameters are set as the joint parameters of the target and ionosphere.Using the analytical model,the error of ionospheric sounding equipment is transformed into the target parameter error in order to achieve joint estimation.The simulation results show that the proposed method can obviously improve the accuracy of the existing algorithms,and has more advantages than the traditional algorithms.