岸基X波段宽带相参雷达海浪信息提取技术研究

发布时间：2019-01-26 13:10

【摘要】：海洋是大自然的天然屏障，它拥有丰富的水资源、生物及矿产资源，对其进行探索和开发利用，是拓展我们人类生存空间的重要途径。我国海岸线绵长，临海广阔，海洋资源十分丰富，这使得研究海洋遥感技术有着非常重要的意义。X波段雷达（XBR）可以对海面成像，是目前监测海洋环境的重要手段。其工作频率为8GHz~12GHz，它以价格低廉、方便可靠、实时全天候以及高时空分辨率等优点在各国引起了不小反响。本文简要叙述了XBR在海洋遥感获取海态参数技术应用上的发展历程以及目前国内外的研究状况。国内外的研究都是基于X波段非相参雷达的，本文提出X波段宽带相参雷达的海浪反演方法。相比于非相参雷达，一方面它可以通过相参积累直接得到海浪的径向速度信息，并且形成的海面图像为复序列，，另一方面采用大带宽可以获得更高的距离分辨率，从而可以更小尺度观测波浪。模拟仿真中采用200MHz大带宽，距离分辨率可以精确到0.75m。本文的主要工作是对岸基X波段宽带相参雷达反演海浪特征参数算法进行分析讨论，提出对雷达回波进行相参积累（二维FFT处理），对同一距离门的海浪速度加权平均得到海浪的径向速度，并对得到的径向速度进行单站矢量合成，即可得到海表层流场。进而对雷达图像进行基于傅氏变换频谱分析的反演算法提取海浪参数。首先，对XBR成像机理进行了理论分析。雷达发射的电磁波以几乎与海平面平行的方式到达到粗糙的海表面，海浪的波动起伏，与相近波长的毛细波发生Bragg共振散射，而同时毛细波又受到较长波长的海面重力波的调制。后向散射回波到达雷达天线，生成海杂波图像。对一系列连续的随时间演变的海杂波图像序列做三维离散傅里叶变换得到雷达图像谱。利用频散关系设计带通滤波器对图像谱滤波，从背景噪声中分离出海浪能量。对图像谱积分，并用MTF对其进行校正得到海浪方向谱，从而可以提取出海浪的一维频谱以及特征参数等信息。仿照SAR图像中提到的有效波高与雷达接收到的回波SNR有线性关系，估计出海浪有效波高。最后，对提出的X波段宽带相参雷达的海态参数反演算法进行了仿真验证。选取P-M谱的派生形式ITTC双参数谱作为海浪靶谱以及选择余弦平方函数作为海浪方向函数，建立三维随机海浪模型。对考虑阴影调制影响以及加入了系统噪声的雷达图像进行相关算法处理仿真。将反演得到的参数与输入参数进行对比分析，结果显示在误差允许范围内，反演算法是合理可行的。
[Abstract]:The ocean is the natural barrier of nature. It has abundant water resources, biological resources and mineral resources. Exploring and exploiting it is an important way to expand the living space of human beings. China has a long coastline, vast coastal area and abundant marine resources, which makes the study of marine remote sensing technology of great significance. X-band radar (XBR) can image the sea surface, and it is an important means to monitor the marine environment at present. Its operating frequency is 8 GHz and 12 GHz. It has the advantages of low price, convenient and reliable, real-time all-weather and high spatial and temporal resolution. This paper briefly describes the development of the application of XBR in marine remote sensing technology for obtaining marine parameters and the current research situation at home and abroad. The research at home and abroad is based on X-band non-coherent radar. In this paper, a wave inversion method for X-band wideband coherent radar is proposed. Compared with non-coherent radar, on the one hand, it can obtain radial velocity information of ocean waves directly by coherent accumulation, and the resulting sea surface image is a complex sequence, on the other hand, it can obtain higher range resolution by using large bandwidth. Thus, waves can be observed on a smaller scale. In the simulation, 200MHz is used for large bandwidth, and the range resolution can reach 0.75m. The main work of this paper is to analyze and discuss the algorithm of wave characteristic parameter inversion of shore-based X-band wideband coherent radar, and propose the coherent integration of radar echo (2-D FFT processing). The radial velocity of the ocean wave is obtained by weighted mean of the wave velocity of the same distance gate, and the ocean surface current field can be obtained by the single station vector synthesis of the obtained radial velocity. Furthermore, the inversion algorithm based on Fourier transform spectrum analysis is used to extract ocean wave parameters from radar images. Firstly, the imaging mechanism of XBR is analyzed theoretically. The electromagnetic waves emitted by radar reach the rough sea surface almost parallel to the sea level. The waves fluctuate and Bragg resonance scattering occurs with the capillary waves of similar wavelengths. At the same time, the capillary waves are modulated by the gravity waves at longer wavelengths. The backscattering echo reaches the radar antenna to generate sea clutter images. Three dimensional discrete Fourier transform (DFT) is used to obtain radar image spectrum for a series of successive sea clutter image sequences. A band pass filter is designed to filter the spectrum of the image by using the dispersion relation, and the wave energy is separated from the background noise. The spectral integral of the image is corrected by MTF to obtain the directional spectrum of the ocean wave, so that the information of the one-dimensional spectrum and the characteristic parameters of the wave can be extracted. The effective wave heights mentioned in the SAR images are linearly related to the echo SNR received by the radar, and the wave effective wave heights are estimated. Finally, the proposed algorithm of sea parameter inversion for X band wideband coherent radar is simulated. A three-dimensional random wave model was established by selecting the P-M spectrum as a derived form of the ITTC two-parameter spectrum as the wave target spectrum and the cosine square function as the wave direction function. Simulation of radar image processing with shadow modulation and system noise is carried out. The inversion parameters are compared with the input parameters. The results show that the inversion algorithm is reasonable and feasible within the range of error.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TN957.52

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