【作者】 吴敏；

【导师】 文必洋；

【作者基本信息】 武汉大学 ， 通信与信息系统， 2011， 博士

【摘要】 高频地波雷达作为超视距雷达的一种,由于其成本低廉并且使用方便,成为近五十年来发展起来的一种新型海洋环境动力学参数(如流场、风场、浪场)和海洋表面移动目标监测设备。特别地,它是对国家200海里专属经济区(EEZ)内大范围海域进行有效的实时监测的一种理想选择。因此,世界上许多国家都投入了大量的精力在高频地波雷达的研制工作上。尽管高频地波雷达具有重大的军事及经济意义,但是它的使用和发展却受到很大的限制,这主要是局限于高频段的生存能力。在高频段,充斥着大量的噪声,干扰及杂波。其中,射频干扰、电离层杂波及海杂波是对高频地波雷达影响最大的干扰,极大地降低了高频雷达的探测性能。尤其是电离层杂波,由于其复杂多变的特性,已经成为世界上限制高频地波雷达进一步发展的最大障碍。因此如何能有效抑制这些干扰及杂波在高频地波雷达未来的发展道路中至关重要。本文正是基于这样的课题背景,对高频地波雷达的射频干扰、电离层杂波及海杂波的抑制方法展开研究.全文的主要工作如下：1.详细的分析了射频干扰在信号处理过程中所表现的特性,为后续干扰抑制提供了有力的依据。同时结合大量的阵列式雷达及便携式雷达实测干扰数据,针对性地从空域及时域角度探讨了两种有效实用的射频干扰抑制方法,并对各方法的适用条件进行讨论。大量的实测干扰数据处理结果表明了算法能有效抑制阵列式及便携式雷达系统所遭遇的大部分射频干扰。2.简要介绍了电离层的结构及变化。基于大量的实测电离层杂波数据,对电离层杂波的特性进行了分析。提出了利用电离层距离／大尺度时间图来获取电离层宏观信息(如电离层的分层结构,层高,是否存在多跳和是否存在漂移等)及估计电离层水平漂移速度的方法。通过对高频地波雷达电离层杂波的时频分析,实现对电离层杂波扰动模式的检测,并在实测数据中成功捕捉到由电离层行进式扰动(TID)所引起的“S”形多普勒变化,同时对扰动的振幅及周期进行估计,且可以判断电离层内部是否出现不均匀体结构,这些都将大大有利于对电离层的预报。并由大量实测数据的观测得出了Es和F层杂波的时频分布规律,并初步分析了其时频变化产生的原因。3.根据电离层杂波在不同方面所呈现出不同特性,分别从空域、距离域及时频域方面对电离层杂波抑制方法进行了研究,并通过对实测电离层杂波数据的处理对各种算法进行了验证和比较。尤其是基于电离层杂波与有用信号俯仰角方向差异,本文提出了使用面阵的特征值分解法,实测结果证明该方法能有效抑制电离层杂波,大幅度改善电离层杂波内的目标检测性能,且使用局限性较小。而距离域及时频域电离层杂波处理方法由于对天线口径没有要求,特别适用于小口径天线,但是它们的使用具有一定的局限性：如距离域处理只能抑制距离相关性强的聚集区强电离层杂波；基于小波变换的时频域处理方法其处理效果严重依赖对小波母函数的选择；而采用S-Method分析的电离层杂波处理只能在扩展型电离层杂波中提取强目标,因此实际使用中可能需要将多种方法结合在一起才能取得较好的抑制效果。4.简要介绍海杂波的形成机理。结合实测海杂波与仿真目标数据,采用基于Hankel矩阵的SVD方法对海杂波进行抑制,该方法能在目标靠近一阶峰边缘,且具有一定信噪比前提下将目标信号提取出来。同时通过对实测海洋杂波的距离域特性分析,提出了一种海杂波距离相关抑制法。实测数据的处理结果证明了此方法能有效抑制一阶峰信号,并能在目标不完全落入一阶峰中心频率位置且具有一定信噪比时,将目标信号从一阶峰中提取出来,从而改善了一阶峰区目标探测性能。更多还原

【Abstract】 As a kind of the Over the horizon radars (OTHR), HF ground wave radar (HFGWR) becomes a new way to get access to the ocean kinetic parameters (such as the current,the wind and the wave etc)and surveille the moving target on the ocean surface for its con-venience and low-cost in the recent 50 years. especially,it is a perfect choice of the real-time and large-coverage surveillance for the 200 sea-mile of a nation. so a lot of nations in the world devote to the research of the HF ground wave radar (HFGWR). Although HFGWR is very important to the military and economic affairs,the develop-ment of HFGWR is quite limited because of the execrable electromagnetic environment in the HF band. There are many kinds of noise.clutter and interference in the HF band. Thereinto,the radio frequency interference,ionospheric clutter and sea clutter have the most significant impact on the HFGWR, and highly degrade the performance of the radar. especially the ionospheric clutter,it is the most serious impediment to the devel-opment in the world for its quite complex and capricious characteristic. Then how to suppress these kinds of interference and clutter is very important to the future of the HFGWR. just based on this background,the thesis research on the method to suppress the radio frequency interference,ionospheric clutter and sea clutter.The main content is as follows:1. The characteristic of the radio frequency interference in signal processing is analyzed in detail.Two effective radio frequency interference suppression method is discussed based on the lots of real interference data received by array and compact radar ,from the spatial and temporal aspect. The suited condition of each method is also discussed. Processing results of many real interference data prove the availability for the array and compact radar system in practice.2. The structure and transformation of the ionosphere is introduced. Some charac-teristic of the ionospheric clutter is analyzed based on the real ionospheric clutter data. Proposing a method using the range/time spectra to get the macroscopical information of the ionosphere (such as the layered structure,the height,the multiple bounce and drifting ionosphere etc)and the horizontal velocity of the drift iono-sphere can be estimated too. The disturbance mode of the ionosphere is detected by the time-frequency analysis. The "S" shape doppler movement induced by the TID(Traveling Ionospheric Disturbance)is captured in real clutter data, at the same time,the amplitude and period of the disturbance is estimated and the irregularity appearance is judged. It is very helpful to the ionosphere forecast. From the obser-vation of lots of the real data,the regular pattern in time-frequency of the Es and F layer is summarized and the reason of the pattern is explained shallowly.3. The method to suppress the ionospheric clutter is investigated from the spatial tem-poral and time-frequency aspects separately according to the different characteristic of the ionospheric clutter. These methods are also validated and compared by pro-cessing the real data. especially, a new method based on EVD using planar array is proposed, which is validated by the processing result of the real data. Processing in temporal and time-frequency domain has no request on the array aperture and quite fit for the small aperture radar system. Unfortunately,there are lots of limitation of these methods:processing in range domain can only remove the strong ionospheric clutter form concentrated area which has a highly correlation in range domain; The method based on wavelets is highly depends on the choice of the mother wavelet function;The method using SM analysis can only detect the target which has a high SNR in the spread ionospheric clutter.4. The mechanism about the sea clutter forming is introduced briefly. The HRR-SVD method is applied to the real sea clutter with synthetic target data,the processing result turn out that the method is effective when the target has high SNR and get near the edge of the bragg peaks. A new method to suppress the sea clutter is proposed based on the real data analysis in range domain.the processing result of the real data prove that the method is effective when the target has a relative high SNR,and out of the position of the center frequency of the bragg resonance.更多还原