Research and Implementation of Noise Suppression in Sea Clutter of X-band Radar
|School||Harbin Engineering University|
|Keywords||X-band marine radar noise suppression ocean surface current band-pass filter significant wave height|
Ocean wave is a common ocean fluctuation phenomenon, and it has an importantinfluence on human activities about ocean, such as exploration, development, militarytechnology, safe navigation and so on. Making omnibearing and comprehensive-meansmonitor on the ocean environment enables human to understand the variation of ocean motiontimely and accurately, and it also meets the needs of both the military and the civilian aspects.With the advantages of high resolution and ease of use, the X-band marine radar has been animportant branch of ocean remote sensing gradually. And it has been attracting more and moreattentions of the ocean remote sensing scientists. Therefore, it has important theoretical andpractical significance to research wave information extraction technology and equipmentdevelopment based on the X-band marine radar.Based on the studied project of our research group, some key problems in the waveparameters inversion progress of X-band marine radar are deeply studied, such as the noisesuppression of co-channel interference, fixed target and rain, the ocean surface currentinversion, the band-pass filter design, the significant wave height inversion and so on. Themain contents are as follows:1．A noise detection method combined the Laplace operator with the improved Laplaceoperator is proposed. Suppression methods of co-channel interference are mostly based onhardware. And most of the software methods lose the wave information while progressing. Soa noise detection method is proposed, and a noise processing method based on anti-distanceweighted interpolation and triangulation grid interpolation are applied. Compared with theresults of median filter and mean filter, the experiment results show that the new methods areeffective.2．After the parameters of the distribution model estimated by Adaline neural network, adetection method based on the spatial and temporal distribution characteristics of the radarecho signals and with the radar time sequence images is proposed. Detection methods oftargets are mostly based on single SAR image. In SAR images, targets have clear edgecontour features, while the edges of the targets in radar images of this experiment changegradually, and do not have obvious boundaries. In order to meet the needs of our project, thispaper gives a detailed analysis of the spatial and temporal distribution characteristics of theradar echo signals, and designs a new detection method. The experiment results show that thenew method can detect the targets quickly and efficiently. 3．A rainfall identification method taking advantage of quality control, surface roughnessparameter, signal to noise ratio and echo intensity mean is proposed. Existing suppressionmethods of rain interference are mostly making use of hardware. And identification methodwith mean and difference coefficient of images can not effectively identify rainfall images inexperiments. So, on the basis of previous research results, the new identification method isdesigned. The noise images slightly affected by the rainfall are filtered in frequency domain.Experiment results show that the new method can identify and filter the rainfall interferenceefficiently.4． An extraction method of the ocean surface current based on Particle SwarmOptimization and a band-pass filter combined with both the fundamental mode dispersionrelation and the boundary of dispersion relation are proposed. Existing band-pass filters havethe shortcoming that the extracted information is not accurate, so the improvement is needed.The ocean surface current plays an important role in the dispersion relation, which is the basisof band-pass filter. So, the first task of band-pass filter improvement is to improve the oceansurface current estimation. Several currently used ocean current extraction methods based onthe principle of least squares method are introduced. Then some existing band-pass filters aredescribed. Experiment results show that these new methods can improve the accuracy ofextracted wave parameters efficiently.5．Methods of outliers rejection and data rarefaction based on the minimum radius and anew piecewise linear inversion method of the significant wave height based on PSO areproposed. The traditional linear modeling method and the basic piecewise linear modelingmethods are introduced, and the detailed basic principles and processes are illustrated. Thispaper proposes demand of outliers rejection and data rarefaction, also gives the correspondingmethods based on minimum radius. Finally experiments on these modeling methods withdealt data are carried out, and the results show that the designed methods are effective.