| With the development of science and technology, considerable interest has been inspired in the ocean .The ocean area takes about two in three of the earth surface. There are various and ample resource in the ocean, such as biologic and mineral resource and energy. The exploitation of these sources seems especially urgent nowadays. As complex as the ocean environment be, ocean work, transition on sea , disaster prediction and national marine security all rely on the mastery and prediction of the basic data of the physical oceanography elements and their variety disciplinarian, including wind, wave, current, tidal, etc.The ship-based X-band radar can be used not only to detect the moving aim but also to determine ocean wave and current. The prominent advantage of this technology is low price, and it's convenient to monitoring the dynamic ocean condition factors in time and all day by using the nautical radar on ship.The writer has attended the research process of the subjects"Wave remote technology based on X-band radar"(4071010404) and"Ocean wave detection technology with X-band radar"(2004AA639670).The ocean wave and current field has been inversed on the basis of"X-band based wave and current monitoring system"principium radar. The writer's work is to estimate the surface current, and to validate the rationality and the accuracy of the method through the numerical simulation and the experiment on sea .The"sea clutter"is formed by radar back signals. Several successive radar images are chosen and changed into digital signal which represents space-time distribution of the back signal intense. The three-dimension spectrum can be obtained by applying FFT to image series. After filtering, integral, and multiplying the transfer function, finally the sea wave spectrum is achieved, and further sea state parameters, such as peak periods, peak frequency wave direction, can be estimated.Current causes the Doppler Effect between observed radar frequency and wave intrinsic frequency. It is necessary to determine the current value for performing the dispersion relationship to filter the radar back wave signal before inversing sea wave field information.This paper carries the Fourier transform to extract wave and current field messages when it is homogeneous. First, the least square multiplication based basic surface current arithmetic is introduced. As the wave bin which has bigger spectra energy is more likely to locate on the dispersion relationship, the most appropriate weighed variance should be chosen in the application of LSM, while the weight is the corresponding spectrum values. It is found that higher harmonics of the dispersion and aliasing effects take great affection on current estimation. To improve the accuracy, retrieving the signal and considering an iterative method can take effect.The accuracy of wave and current extraction method can be tested by numerical simulation. This paper chooses P-M wave spectrum to simulate image series of sea surface on the basis of linear theory. Shadowing and tilt modulation are main imaging mechanisms which affect the formation of"sea clutter", considering this with current together,"sea clutter"images series is simulated. Applying wave and current extraction arithmetic to obtain wave and current information, and comparing with input values, and then the arithmetic is proved feasible.The precision of the Fourier method is obtained by the experiment on sea, the mean error of surface current velocity and direction, peak frequency and direction separately are 0.13m/s,13o, 10% and 5o。It's proved that the arithmetic accuracy is rather satisfying, especially in wave direction detection, which is far advanced than other remote sensing method.
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