Study On Remote Sensing Mechanism And Retrival Method Of Ocean Wave And Current With X Band Radar

X-band radar can image sea surface. By analyzing the temporal and spatial structure of the image sequences, the sea surface dynamic parameters related to ocean waves and sea surface currents can be calculated using corresponding inversion algorithm. In this research, which is Instrument Developing Project of the Chinese Academy of Sciences named'X band radar for ocean physical parameters', some problems related to retrieving ocean wave and surface current parameters from X band radar image sequences were investigated.In this dissertation, we briefly summarize the history 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. Based on this, the characteristics of radar sea echoes for different polarization at high incidence angle are analyzed in detail. Based on the fact that different polarization has different imaging mechanism, a wave and current monitoring system based on dual polarized X band radar, with independent intellectual property rights, is developed.An algorithm to retrieve sea surface current and wave parameters from X band radar images has been developed, and then the numerical simulation of land-based X-band radar sea clutter was done. The relevant ocean environment factors and the radar system noises that influence the observation of the sea surface current and ocean wave are analyzed and discussed. The key factors that influence the inversion accuracy were given by extracting the ocean wave parameters and surface current from the simulated radar image sequences.An experiment lasted six-month is carried out in the North of Yellow Sea using the newly developed X-band dual-polarization radar system. A great number of radar image sequences were obtained simultaneously with observations of ocean wave and current by wave buoy and sea current meter. Following the inversion algorithm described 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 the standard mean square roots of significant wave height, dominant wave direction, average wave period, sea surface current speed and direction for HH polarization are 0.18m, 21o, 0.55s, 0.15m/s and 21.1o, respectively and For VV polarization, they are 0.18m, 15o, 0.49s, 0.12m/s and 19.4o, respectively. It is shown that VV polarization has the advantage over HH polarization to measure the ocean wave parameters and sea surface current based on our experiment. The reliability and practicability of the remote sensing system of X band radar are also demonstrated.In addition, a Radon transform algorithm for retrieving ocean wave parameters from X band radar images is proposed. First, the textural feature of radar sea clutter images are transferred by Radon transform to retrieve wave parameters, which are ocean wave direction, wave length, velocity and period from radar image series. The inherent 180°ambiguity of wave direction is resolved directly from radar images based on the cross correlation technology. Compared with other analysis method, the new algorithm has high accurate and simple.Finally, a set of software for acquiring the radar data and extracting sea surface dynamics parameters from X band dual-polarized radar system is developed using Visual C++ under Windows XP.