利用海杂波反演大气波导环境中折射率的关键技术研究

项目名称： 利用海杂波反演大气波导环境中折射率的关键技术研究

项目编号： No.61002008

项目类型： 青年科学基金项目

立项/批准年度： 2011

项目学科： 金属学与金属工艺

项目作者： 赵小龙

作者单位： 天水师范学院

项目金额： 7万元

中文摘要： 大气波导是由于近海面大气修正折射率随高度的反常下降，使电波射线向下弯曲的曲率大于地球表面的曲率，从而将电磁能量陷获在波导结构内的电磁波异常传播现象。大气波导的出现不仅可以使电磁波偏离原来的传播方向，而且能够使电磁波以较小的衰减沿波导传播到很远的地方，对无线电管理、雷达及微波通信等电子系统应用、电子战攻防手段等影响显著。因此，实时、准确地预测预报大气波导折射指数成为电子系统性能评估和系统设计的关键。海杂波反演技术由于实时性、保密性、设备简易等优点，是一种极具潜力的大气波导环境预测技术。 利用Helmholtz方程近似得到的抛物型方程能有效解决近水平小仰角的电波传播问题，结合遗传算法、神经网络等智能算法对中性层结蒸发波导的特征参量―#8213;波导高度进行了反演。以波导高度20米的中性层结蒸发波导为例，数值仿真结果表明遗传算法与抛物型方程傅立叶分步算法的结合是实现蒸发波导环境中折射指数分布预测预报的有效途径。

中文关键词： 大气波导；修正折射率；抛物型方程；遗传算法；神经网络

英文摘要： Marine evaporation duct is a nearly permanent propagation mechanism due to the abrupt changes in the vertical temperature and humidity profiles just above the large ocean surface. Its existence greatly strengthens or degrades the capability of the naval Radar, Communication, and Electronic Support Measures (ESM) system. Environmental information based on the effective duct can accurately predict the EM-wave propagation, and exactly assess the performance of electronic weapons systems. Based on the characteristic parameter of the atmospheric duct, such as modified refractivity, the ray-tracing technique and the parabolic equation by Fourier split-step method were introduced to analyze the anomalous propagation of electromagnetic wave in marine evaporation duct. The simulation results show that evaporation duct can significantly trap some radio rays to extend the propagation distance of EM wave and result in the appearance of radar blind zone. Therefore, the real-time, accurate forecasting and prediction of refraction index in atmospheric duct is key factor for performance evaluation and system design of electronic systems. By Genetic Algorithm (GA), Neural Network (NN) and Fourier split-step method (FSS) and for neutral layer of evaporation duct with the duct height 20m, Refractivity from Clutter (RFC) is used to predict and forecast the refractive index profile of evaporation duct. Inversion of atmospheric refractive index profile using radar sea clutter has an obvious advantage which can use ship-borne radar remote sensing equipment to estimate the current atmospheric refractive index profile of the vertical and horizontal distribution. Meanwhile, the inversion problem is converted to statistical estimation of parameters. In contrast with traditional meteorological measure, refractive index profile from radar sea clutter does not need to add additional measuring equipment, and real time, military secrecies is better. Therefore, the RFC technique is an efficient method to estimate atmospheric refractive index profile.

英文关键词： Atmospheric duct; modified refractivity; Parabolic equation;Genetic Algorithm; Neural Network