Suppression Of First-Order Sea Clutter For Shipborne Hf Hybrid Sky-Surface Wave Radar

With the continuous development of high-frequency radar technology,the hybrid system high-frequency radar based on sky-wave launch-ground wave reception(shipboard platform)combines the advantages of h igh-frequency ground wave and high-frequency sky wave radar,which greatly improves the detection power compared with traditional high frequency radar,and the coverage is wider.Because the transmitter is located in the inland area,it has better concealm ent and stronger survivability;and because the shipboard receiving platform has more flexibility and maneuverability,it also effectively improves the detection capability of high-frequency radar due to the increased time for early warning,has significantly improved our response capabilities.Under the system of the shipborne high-frequency hybrid sky-surface wave radar,the electromagnetic wave is obliquely incident into the ionosp here,reflected by the ionosphere to the sea surface and detected targets,and then propagated along the surface of the ocean in the form of ground waves to the receiver located on the ship.Therefore,the sea clutter is affected by the superposition of fa ctors similar to the bistatic angle of the shore-based bistatic radar and ionospheric disturbances,which causes the first-order sea clutter spectrum to be more complicated after strong interference,and the clutter broadening and frequency shift will be s erious Affecting targets located near the clutter area is not conducive to effective target detection in the later period.In this paper,based on the detection principle of the shipborne high-frequency hybrid sky-surface wave radar,the characteristics of the sea clutter under the high-frequency radar collection system of the Tianfa ship are combined with the measured data.The time-frequency analysis tool is used to preprocess the sea clutter data,and then combined with the sea clutter model,the measured sea clutter and ionospheric clutter are suppressed.The research in this paper can provide a certain reference and technical support for the direction of clutter suppression in the hybrid system of sky-wave launch-ground wave reception(shipboard platform)in the future.This article revolves around the above analysis.The main research contents include:First,based on the system of the shipborne high-frequency hybrid sky-surface wave radar,because the propagation path of electromagnetic waves is induced by ionospheric reflection,ionospheric interference is introduced;the radar receiving platform also has motion,resulting in different relative speeds o f sea clutter relative to the ship across the sea,resulting in broadening of sea clutter.Secondly,the sea clutter suppression technology of the shipborne high-frequency hybrid sky-surface wave radar is divided into two steps.The first is pretreatment,because the electromagnetic wave is reflected by the ionosphere,the ionosphere has time-varying non-stationary characteristics,linear and nonlinear concentration Clutter will cause frequency shift and broadening of the sea clutter spectrum in post-processing.Common methods include time-frequency analysis,including short-time Fourier transform(STFT),Winger-Will distribution(WVD),and S-method method.Finally,it is based on a single-dimensional clutter suppression process in the early stage,such as the spatial domain processing method.Subsequent clutter suppression methods mainly study space-time joint processing,namely space-time adaptive processing(Space-Time Adaptive Processing,STAP).The data processing dimension covers the distance-Doppler(R-D)domain and the angle-Doppler(Angle-Doppler)domain.As for the idea of space-time processing,there are two aspects of dimension reduction and rank reduct ion.And after the verification of the measured data,performance evaluation is proposed.