【作者】 康士峰；

【导师】 葛德彪；

【作者基本信息】 西安电子科技大学 ， 电磁场与微波技术， 2000， 博士

【摘要】 在雷达设计和性能分析以及微波遥感应用等研究领域，十分关注地球陆地和海洋表面的微波电磁散射和传播特性。本文从以下几方面对地海面微波散射和传播特性进行了分析和研究，并讨论了在有关方面的具体应用： 首先介绍了我国第一部地基多波段全极化微波散射计、第一部L波段单通道HH极化机载杂波雷达和第一部L波段多通道VV极化机载杂波雷达的系统组成、校准、测试和性能分析方法。基于以上测量系统，组织了多次大规模的地面和空中试验，为本文研究内容和其它相关课题提供了大量有价值的数据。 散射计和雷达系统的校准是决定散射系数测量数据可靠性的关键问题。本文对散射计和机载杂波雷达的绝对校准技术进行了详细分析，采用无源或有源校准器（ARC）分别对其进行了实际测试、误差分析和修正，保证了多波段散射计数据2.0dB和机载雷达杂波数据2.5dB的较高精度。 对多波段全极化散射计的时—频域测量方法进行了研究，分析了典型地物的杂波特性并评价了相关模型的适用性；首次对海面散射特性（杂波）进行了长时间、多海态、多波段、多极化、大范围入射角的系统观测，对数据进行了统计处理并与Rayleigh分布、Log-normal分布、Rice分布、Weilbull分布和K分布进行了比较，揭示了海杂波特性与有关参数的一般关系。 使用机载杂波雷达对我国多种典型地形地貌和东南海域进行了多航线多架次系统的杂波测量，分别给出了不同类型下地海杂波的统计特性，提取了统计模型的特征参数。进一步用分形模型和Gaussian模型（Gaussian相关和指数相关）下的Kirchhoff近似并结合常数γ模型、指数模型和实测数据进行了分析比较，测量数据和研究结果对我国机载预警雷达的试飞区域选取和机载雷达的性能检验具有重要意义。 将电磁场数值算法即抛物型波方程（PE）的分步Fourier变换方法和空-时二维动态分形地海面的非线性动力学模型相结合，在考虑实际大气环境指数折射率模型情况下，分析计算了传播损耗或传播因子与大气参数和地海面分形参数的统计关系。结果表明，场强起伏可达20dB，传播距离越远、收发天线相对高度越大起伏越强且呈现与地海面相似的分形特征。 地海面散射特性的产生和演化可以从非线性混沌现象中得到解释，其外在几何表现又可以用分形来描述。本文运用混沌理论和分形几何对散射计和机载雷达杂波数据进行了混沌和分形特性分析，计算了Lyapunov指数、相关维数、谱维数、分形和多重分形参数，首次指出杂波的动态变化不仅对海杂波小擦地角同极化，而且对多波段较大入射角交叉极化地、海杂波特别是机载雷达杂波都可以用非线性方法来处理，但地、海杂波可能具有不同的特点和参数，揭示了杂波的短期可预测性和对杂波中目标检测的重要意义。 地海面微波散射和传播特性研究及其在雷达和遥感中的应用 小波分析优于Fourier分析之处在于它的时频二维自适应高分辨特点，本文利用小波的自相似性对杂波的多尺度分形特征进行分析。通过比较随机函数、确定性函数、分形函数以及杂波数据的连续小波变换特征，表明分形函数和杂波在较大尺度范围内都能表现出明显的自相似性。结果进一步揭示了杂波的分形特征和小波分析检测分形杂波的有效性，同时比较分析了对检测分形特征效果明显的小波基特点。根据分形杂波在多尺度小波变换域上的特征可以重构或生成杂波，为杂波的仿真提供了又一有效途径。 基于理论和实际测试，本文对任意姿态机载PD雷达体制下的三维地杂波算法进行了研究和实现。这种模拟方法根据雷达功率方程，综合考虑了三维数字地形信息、散射回波的频率模糊和距离模糊、地形地物散射特性建模、任意姿态载机和雷达坐标的变换以及地形遮蔽算法等，可以仿真出与理论分析和实际测试相一致的二维距离－多普勒杂波图以及散射系数图像和雷达可视区图像。 作为对理论和实验成果的具体应用，本文提出了对地球表面微波散射特征的遥感分类方法，基于多波段多极化多入射角相关测试数据和散射模型，利用人工神经网络（ANN）对八种地形地物进行了分类实验。结果表明AN－N在一定噪声干扰或散射系数的一定变化范围内仍然能够作出较好分类，显示了ANN作为遥感分类器的优越性和实用性。 在本文的最后，利用欧空局 ERS－l／2遥感卫星平台上的散射计所测得的全球范围C波段VV极化散射系数分布数据，结合中国陆地表面地形地貌特征，分析了我国散射系数宏观的分布特点和变化趋势，统计和比较了三种典型环境散射系数随时间的变化规律和动态范围等参数，首次提出我国陆地五种散射类型和相关地理区域的划分及环境特征。其结果可为我国陆地环境的微波遥感和军事雷达特别是机载和星载雷达的目标检测杂波背景评估提供重要的依据。更多还原

【Abstract】 Microwave scattering and propagation characteristics of terrain and sea surfaces are paid more attention in the design and performance analysis of radar and remote sensing. These problems are studied and some applications are discussed as follows: The first ground-based multi-band polarization microwave scatterometer, the first L- band single-channel HH polarization airborne radar and the first L-band multi-channel VV polarization airborne radar are developed in China to meet the needs for the theory study and applications. The specifications of system, calibration, measurement and analysis methods are introduced. Many tests have been made on the ground and in the air with these measurement systems and provide this paper and other research subjects with a lot of valuable data. The calibration of scatterometer and radar system is a key problem to the precision and reliability for the determination of scattering coefficient from experiment data. The absolute calibration techniques of scatterometer and airborne clutter radar are analyzed by using passive and active calibrators. The data precision is within 2.0dB or 2.5dB by means of error modification. The measurement methods of scattering coefficient in time and frequency domain are studied. Four kinds of terrain clutter and some models are analyzed. The scattering characteristics of sea surfaces are observed with long-term, multi-state, multi-band, multi-polarization, and multi-angle using the same one scatterometer for the first time. The obtained data are processed and compared with Rayleigh distribution, Log-normal distribution, Rice distribution, Weilbull distribution and K distribution. The general relation between clutter and the parameters of radar and sea states is obtained. Multi-course and multi-sortie airborne clutter measurement of many kinds of typical terrain and southeast sea area in China has been carried out. The statistical characteristics for different kinds of terrain and sea clutter are given and the model parameters are extracted. The Kirchhoff approximation based on fractal model and Gaussian model (Gaussian or exponent correlation) are analyzed and compared with constant y model, exponent model and experiment data. The data and results derived are more important to the choice of flight-test area of our AEW radar and to the test of airborne radar performance. Combined the Split-step Fourier transform of parabola equation (PE) with non-linear dynamic model of space-time 2D fractal terrain and sea surfaces, statistical relationships between propagation factors and fractal parameters are calculated and analyzed considering the exponent model of atmospheric refractive index. The results show that the field can vary as high as 20dB. The variation becomes stronger and shows some III fractal characters for longer transmitter-receiver distance and altitude difference. The production and evolvement of terrain and sea scattering may be explained from non-linear chaos and the geometry may be described with fractal. The chaos and fractal characteristics are analyzed using the data measured by scatterometer and airborne radar. Lyapunov index, correlation dimension, spectral dimension, fractal or multi-fractal parameters are calculated. It is pointed out for the first time that the clutters also show chaos and fracta~ character at larger grazing angles, multi-band, cross-polarization and in the conditions of airborne measurement, but their characters may be different. This is important to t更多还原