Research On Electromagnetic Scattering Of First-order Sea Clutter For Shipboren High Frequency Sky-surface Wave Radar

The shipborne high frequency sky-surface wave radar is a further extension and development of the sky-surface wave radar system under the traditional fixed platform.The mobility is raised than the high frequency sky-surface wave radar.However,due to the influence of shipboard platform movement,the first order sea clutter,which is the source of sea surface parameter inversion and the background of sea target detection,presents more features.Therefore,the study of the first-order sea surface echo spectrum is helpful to the theory and application of the shipborne high frequency sky-surface wave radar in the field of target detection and ocean remote sensing.In this paper,the space-time distribution and widening characteristics of the first-order sea clutter are analyzed from the perspective of signal processing.From the perspective of electromagnetic scattering theory,the radar cross section of the first-order sea clutter radar is studied.Firstly,the geometric model of the hybrid propagation path of the high-frequency radar is established,and the elliptic distribution of the sea-surface scattering trajectory is explained.The first-order sea clutter doppler frequency formula is deduced,and the influence of the system layout on the space-time distribution curve is analyzed.In addition,under the arrangement of two arrays,the first-order sea clutter broadening effect under the influence of grazing angle and bistatic angle,ship motion and ionospheric phase pollution is studied for single antenna and uniform linear array.The first-order sea clutter broadening effect under multi-factor complex is analyzed.Then,from the perspective of electromagnetic scattering,the electric field of the frequency domain is deduced from the geometric relationship of the hybrid propagation path and the electric dipole is used as the excitation source to propagate through the hybrid path.According to Walsh's electromagnetic scattering theory,the ionospheric and sea surface are assumed to be stochastic processes,and the first-order sea-clutter RCS equations of monostatic and bistatic high frequency radar under mixed propagation path are deduced.The effects of different ionospheric disturbance states,system layout,wind direction and radar operating frequency on the first-order spectrum are simulated and analyzed.And the first-order sea clutter model is validated by the measured data collected by the bistatic high frequency sky-surface wave radar.Finally,according to the geometric displacement relation of shipboard platform motion,the electric field equation of mixed propagation path is fixed,a nd the first-order sea clutter RCS equation of the ship-borne high-frequency ra-dar is derived in the uniform linear motion of the shipboard platform.The influence of different parameters on the first-order sea clutter spectrum is studied by simulation experiment.Due to the complex environment of the sea,the ship in the process of uniform movement must exist in the ship's six-dimensional movement.Based on the definition of six-dimensional motion of the ship and the six-dimensional motion model,the influence of six-dimensional motion on the scattering path of the sea surface is analyzed.On the basis of the above work,the first-order sea clutter RCS equation under six-dimensional motion is deduced,which indicates that the six-dimensional motion makes the first-order sea clutter produce the modulation spectrum,and the influence of sea state on first order spectrum is analyzed.