Study On Retrival Algorith Of The Ocean Wave Parameters Information With X Band Radar

There are not only various and ample natural resources in the ocean, such as biologic and mineral resource, but also is a broad space for kinds of activities, marine transportation, offshore platform operations, navigation vessels and so on. As extremely complex as the ocean environment be, exploitation of marine resources, national security and disaster prediction all rely on the accuracy mastery and prediction of the physical oceanography elements information and their variety disciplinarian, including ocean winds, waves, current, etc.Moreover, oceanographic monitoring is the essential work of study of ocean environmental elements. Therefore, the development of oceanographic monitoring technology and information extraction technology is of great significance.Then X-band radar went into people’s horizons with the advantage of high space-time resolution. and was promptly applied to the oceanographic monitoring field.The outstanding characteristic of X-band radar is low price, stable performance,, easy installation on the working platform and convenient to monitoring the dynamic ocean condition factors in time and all day, such as ocean wave, one of the most basic factors of the ocean environment.As the electromagnetic waves emitted by X-band radar arrive on ocean surface,they would be interacted with the short waves,whose wavelength are equal to the integer times of one half of the radar electromagnetic, then Bragg resonance scatteringis accomplished. When the backscatter scattering echo signals are received by radar antenna and shown on the radar screen. The phenomenon called sea clutter is done.Moreover, the longer waves become visible in the radar images by modulating the short Bragg scattering waves. In thistreatise, we briefly summarize the advantages and disadvantages of several commonly methods used for oceanographic monitoring and recent status of the research on ocean remote sensing using X band radar,and present the ocean remote sensing principle and imaging mechanism of sea surface by X band radar firstly.Based on this, the algorithm for determining the wave information from X band radar images was studied, especially in the surface current determination. In this dissertation, LSM(Least Squares Method),iterative LSM and NSP(Normalized ScalarProduct) are used to obtain the surface current respectively, the inversion results proved the advantages of NSP. It is worth mentioning that variable step method was adopted in NSP, which reduces the calculation time greatly. Then,the dispersion relation current velocity took into account was used to filter the wave spectral components, and the wave directional spectrum was acquired by modifying the radar image spectrum with the experiential transfer function.Finally, the other parameters included by the wave information were determined based on wave directional spectrum,such as peak period,peak wavelength,wave direction,etc.Numerical simulation is not only important for understanding X band radar imaging principle, but also can be used to test the accuracy of wave and current extraction algorithm.Based on linear theory,we select JONSWAP spectrum and a squared cosine distribution to simulate radar image series of sea surface under wind sea state and swell sea state combined with geometric imaging model.applying current and wave extraction algorithm to simulated radar image series for current and wave information,and comparing with input values,the inversion results is proved feasible.Moreover,comparative experiment at sea is carried out in North of Yellow using X band radar system.Following the inversion algorithm above,ocean wave parameters and sea surface current are retrieved from the collected X band radar images. The results are in a good agreement with these in-situ. It is shown that standard mean square roots of sea surface current speed and direction, significant wave height, dominant wave direction, average wave period for HH polarization are. The results show that the inversion algorithm used in this dissertation has obvious advantages.