Research On Sea Clutter Supression In Hybrid Sky-surface Wave Radar Based On Space Time Adaptive Processing

Based on the hybrid operating mode of sky-wave transmitting gand ground-wave receiving,high-frequency(HF)hybrid sky-surface wave radar is a bistatic radar.It's capable of detecting targets thousands of kilometers away,covering millions of square kilometers and detecting stealth aircraft.HF hybrid sky-surface wave radar can be achieved on our vast sea area for effective and economically remote monitoring and maritime remote sensing.However,the clutter background of HF hybrid sky-surface wave radar is complex,and the sea clutter pollution is serious,which affects the effective detection of ship targets seriously.Therefore,the research on spread sea clutter suppression is of great theoretical and practical value to improve the performance of radar.Firstly,this paper study the internal mechanism and characteristics of the broadening sea clutter for HF hybrid sky-surface wave radar.The firs-order sea clutter spectrum characteristics are related to incident angle,bistatic angle and ionospheric state.Among them,two methods are used for the analysis of the influence of ionosphere on sea clutter broadening.On the one hand,under the different accumulation time,the ionospheric disturbance makes the influence of the first-order sea clutter different;on the other hand,the influence of ionospheric perturbation on the first order sea clutter is analyzed by highorder ambiguous function(HAF).Based on this criterion,the criterion of the existence of ionospheric disturbance is put forward.Secondly,this paper theoretically analyze the space-time coupling of first-order sea clutter,meanwhile derivate the rank of the first-order sea clutter in ideal situation for the first time.The reduced dimension STAP(RD-STAP)algorithm with multiple training snapshots need to analysis the correlation between the snapshots,so the correlation between the test snapshot and the train snapshots is analysis from Doppler dimension,azimuth dimension and distance dimension.The results of correlation of Doppler dimension and azimuth dimension determine the local processing freedom of the RDSTAP algorithm.The result of distance dimension is based on multiple snapshots selected,the correlation coefficient threshold is set to 0.7,which provides a theoretical basis for the following algorithm research.Thirdly,in the cases that there are multiple training snapshots,this paper study three RD-STAP algorithm: Joint Domain Localized STAP,Improved Joint Domain Localized STAP and Space-Time Multiple Beam STAP.In this paper,the performance of the three algorithm is compared with the change of the target SNR and main calculation before and after the sea clutter is suppressed.Finally,it is difficult to find a case where multiple snapshots(those snapshots and test snapshot are independent and identically distributed(IID))are found in the adjacent snapshots when the detection snapshot is disturbed by the fast phase-path disturbance.In this paper,a Single-snapshot STAP algorithm based on fast approximation power iterative algorithm(FAPI)is proposed.Unlike the airborne radar,the clutter background of HF hybrid sky-surface wave radar is complex,and the clutter subdomain dimension of its clutter covariance matrix can't be determined.Based on the objective function of FAPI algorithm,this paper presents the FAPI-STAP algorithm data construction evaluation criteria and the clutter subspace dimension estimation algorithm based on dichotomy method.The improved algorithm not only estimate the clutter dimension quickly,but also the calculation speed is fast.Meanwhile,this paper evaluates the performance of the FAPI-STAP algorithm from two aspects: the change of the target SNR before and main calculation before and after the sea clutter is suppressed.