Moddeling and Analysis on Sea Clutter of Ship Borne High Frequency Surface Wave Radar
|School||Harbin Institute of Technology|
|Course||Information and Communication Engineering|
|Keywords||sea clutter shore-based HFSWR ship borne HFSWR radar crosssection digital spectrum simulation|
Marine resource is one of the most important resources of the21st century. It is asignificant issue faced by all countries how to exploit the marine resourcesrationally; what’s more, protection of the territorial waters from external violation isessential. Due to the fluctuations of the ocean surface, frequency shift on the echopower spectrum will be generated when the radar signal is transmitted to the oceanwaves, thus the detection of the target will be affected. The echo of the wave thatcauses the frequency shift of the spectrum is known as sea clutter, and the value ofthe frequency shift is known as the Bragg frequency. The research and applicationon the power spectrum of sea clutter is significant in decreasing the influence of thesea clutter on the detection of the useful target, extraction of the ocean surfacecurrent information, and ocean weather forecast.There are several forms of the High Frequency Surface Wave Radar (HFSWR)platform configurations: shore-based, ship borne, airborne et al. The powerspectrum densities of the sea echoes of shore-based and ship borne HFSWR aremainly researched in this paper. The power spectrum density of the shore-basedHFSWR has already been researched very sufficiently, and has gotten someachievements on both theory and experiment all over the world. The deduction ofthe sea clutter model and the radar cross section of shore-based HFSWR is studiedfirst. According to the boundary perturbation theory, the radar cross section of thesea clutter can be derived by making Fourier transformation of the ocean surface.With numerical calculation process such as normalization, solution of the nonlinearequations and Romberg integration, the first and second order radar cross sectioncan be simulated, and the graphics of digital spectrum of the sea clutter received byshore-based HFSWR can be derived. The influence of the sea conditions on theamplitude and shape of the sea clutter digital spectrum is also studied.Because of the fluctuation of the ocean, the actual ship borne platform willpresent motions of different level. Six oscillating motions of the actual ship borneplatform are included in this paper besides the forward motion. Movements of theship borne platform under different sea states are researched, and the influences ofthe platform motion on the detection of the radar antenna are also discussed.Different from the shore-based HFSWR, the power spectrum density of the shipborne HFSWR will be widened because of the motion of the ship borne platform.Under the assumption that the velocity of the platform is a constant on the foundation of the floating motion and that the source is imposed as a vertical dipole,the first-order radar cross section of the sea clutter is derived from the first-orderfield equation. The derived model is testified and the influence of different reasonson the first-order digital spectrum of the ship borne HFSWR sea clutter is simulated.On the other hand, the expression of the echo signal is derived from the analogsignal transmitted by radar, and the spectrum of the sea clutter can also be deducedby making Fourier transformation to the echo signal. The fluctuation of the oceanwave is random, thus the amplitude and phase of the echo spectrum are randomsequences. The statistic properties of the amplitude and phase of the echo spectrumare discussed in this paper, and a new quantitative correlation test method of therandom sequence is proposed in this paper: the differentiation method. Thetheoretical foundation of this method is given, and for Gaussian distributed andlognormal distributed colored noise sequence, the correlation test results are derivedfrom several tests.