海上湍流对雷达波传播影响模拟研究

基于海洋大气近地层相似理论,给出了大气折射指数和微波波段湍流强度垂直廓线模型;基于一维Kolmogorov湍流谱,数值模拟随机瞬变大气折射指数,并将其叠加在大气折射率垂直廓线上,建立了海洋大气近地层考虑湍流影响的大气修正折射率垂直廓线模型.利用海面水文气象观测数据和美国海军高级传播模型,数值模拟了蒸发波导和湍流对雷达波传播和雷达探测性能的影响,发现:海洋大气近地层湍流在一定程度上增大了蒸发波导内雷达波传播损耗,减弱了雷达对海面目标的超视距探测能力;而在蒸发波导高度以上部分空域,湍流效应在一定程度上减弱了雷达波传播损耗;因此,在定量评估舰载雷达探测性能时有必要考虑蒸发波导和湍流的综合影响.     

近海面光学与微波波段大气折射率结构常数比较分析

大气湍流的变化影响红外和雷达波的传输,红外波段和微波波段在近海面受大气湍流的影响不同。折射率结构常数表征大气湍流强度,本文对近海面大气环境下的光波段和雷达波段传输的湍流强度做了理论计算和仿真分析,结果表明,在近海面气象条件下,各种光波长湍流强度比较接近,且大于微波波段湍流强度;光波段和微波波段湍流强度都随气海温差增大而增强。     

海上湍流效应对大气波导传播的影响

海上的湍流大气会引起海上大气波导传播中能量的严重泄漏,进而影响雷达对目标回波信号的正确判断。文中通过利用微波测距机进行连续测距,反算出海面上大气折射率的起伏变化,继而得到能够反映湍流特征的折射率随机扰动项,再将折射率扰动项分别加入到抛物方程模型和射线追踪技术中进行了湍流环境下的传播损耗和射线轨迹计算。计算结果表明,在海上波导传播计算模型中考虑折射率扰动项,可以更加合理地进行雷达系统效应评估,准确地反映大气湍流对海上电波传播的影响。     

海上蒸发波导PJ模型在我国海区的适应性初步研究

 本文简述了海上蒸发波导的测量方法,分析了气象水文参数测量误差对Paulus-Jesk(PJ)模型的影响,利用近两年海上实验采集的我国部分海区在各种气象条件下蒸发波导大气折射率剖面和海面气象水文数据,研究了PJ模型的适用条件,以及PJ模型估计出的蒸发波导高度与实测结果的偏差情况,可为蒸发波导模型的修正和蒸发波导条件下雷达最大探测距离的预测提供参考.     

基于蒸发波导传播的雷达定位误差研究

大气参数满足一定条件(修正折射率梯度小于0)时会形成大气波导,利用大气波导可实现雷达的超视距探测。由于近海面易形成蒸发波导,利用蒸发波导实现雷达的超视距探测已成为目前舰船雷达最实用的方法之一。雷达电波射线在不均匀大气中传播时会产生折射误差,为提高舰船雷达的定位精度,必须研究雷达在蒸发波导中超视距探测时的大气折射误差。根据电波传播理论,利用电波射线描迹技术,建立了舰船雷达在蒸发波导中实现超视距探测时的大气折射误差模型。仿真实验表明,蒸发波导条件下雷达超视距探测目标时的大气折射误差较大,且计算时不能采用常规的折射误差计算方法。     

空间目标监视雷达大气折射修正技术研究

无线电波在大气层中传播时,大气介质的不均匀分布会对电波产生折射效应,从而影响雷达的探测精度。对于航天目标的雷达探测,影响无线电波的介质主要是电离层。本文利用实时TEC数据同化的方式,建立了电离层电子密度现报模型,实现了电离层折射率剖面的实时构建。在此基础上,利用射线描迹法完成了航天目标雷达探测的折射误差修正。结果表明,相对于单纯使用电离层经验模型-国际参考电离层(International Reference Ionosphere, IRI)模型,利用电离层同化现报模型建立的电离层折射率剖面可大大提高折射误差修正的精度。     

一种蒸发波导预测的改进模型

利用大概率的近海面蒸发波导效应实现雷达超视距探测已成为目前岸基、舰船无线电测量系统的关键技术之一。在实际应用中,需要由蒸发波导参数建立大气修正折射率剖面的预测模型。针对目前常用的蒸发波导预测只含波导高度和海面修正折射率两个参数,没有考虑波导强度的影响,使得该模型存在一定的误差的现状,通过在原有模型的基础上增加波导强度的影响,建立了高精度的改进模型,使得蒸发波导预测模型的精度得到了有效提高,进而可进一步提高雷达超视距探测精度。实验验证表明,蒸发波导预测改进模型的精度远远高于常用的模型,且波导强度越强,则改正模型的精度越高。     

基于多波长激光探测海洋大气波导机理及实验研究

海洋大气波导是能够影响侦察预警探测装设备和常用民用航型保障设备的重要大气环境因素。本文采用一种基于激光探测遥感探测大气波导的技术,通过分析计算典型海洋大气多波长激光传输特性、光波波段折射率结构常数与激光探测大气波导机理模型。同时通过自主研制的激光雷达在三亚等地进行大量实践大气波导探测,并同步开展探空气球探测低空100m范围内的温度和湿度剖面,采用温度和湿度剖面获取折射率剖面和激光传输的消光系数垂直分布以及光波段的折射率结构常数分布,实验分析初步表明用激光探测大气波导尤其是海上大气波导尤其是蒸发波导的可行性。     

全国大气折射率剖面预测方法

地球上空的不均匀大气对雷达探测性能具有较大的影响,为提高雷达探测精度,首要问题是能够精确预测到雷达作用区内的大气折射率剖面.针对我国国土面积大、地形复杂、大气环境参数变化多样的特征,根据无线电气象学理论,采用全国大气环境栅格技术,提出了一种全国大气折射率剖面预测方法.根据我国大气环境分布特征,把全国分成1 840个栅格...     

负折射对海上光电传播特征的影响分析

由于可见光、红外等光电设备对近海面(50 m范围内)的低空目标进行跟踪探测时受大气折射效应影响显著,导致探测距离增大或缩短,伴随出现多目标现象,增加了系统的虚警概率,干扰目标的跟踪.基于近海面海气通量算法与射线跟踪算法建立海上光电传播特征评估模型,并利用2009年12月在黄海北部某海域开展的负折射环境下光电探测的实验数...     

基于雷达海杂波的大气折射率剖面估计技术

基于雷达海杂波的海洋大气折射率剖面估计简称为RFC,RFC技术能实时地将雷达海杂波中携带的大气折射率空间分布信息提取出来,为舰载雷达和通信系统提供环境评估信息.从Bayes参数统计估计和多参数最优理论的角度简要介绍了RFC的基本原理,其次对其研究历史和研究现状作了介绍,对其有待解决的四个关键问题:传播模型、环境模型、海杂波模型及反演算法作了重点探讨,对其下一步的研究方向作了展望.     

Tropospheric radio propagation assessment

The status of tropospheric radio propagation assessment is reviewed and recent advances in this area are described. Special emphasis is given to anomalous propagation in a marine environment. Modeling and measurements of ducting phenomena caused by the oceanic evaporation duct and by elevated refractive layers are discussed. The modeling involves extensive numerical calculations of waveguide propagation, ray-tracing techniques, and empirical relationships. Effects such as sea-surface roughness and horizontal inhomogeneity are also addressed. The models have been compared with extensive measurements in a variety of geographic locations. Worldwide radio refractivity climatologies have been compiled. A propagation assessment system, called the "Integrated Refractive Effects Prediction System" (IREPS), has been developed and successfully tested. It uses a small computer with interactive graphic displays and provides the user with performance assessment of communications and radar equipment based on prevailing atmospheric conditions. Environmental inputs into the system consist of surface measurements and profiles of atmospheric refractivity either calculated from radiosonde balloon data or measured by microwave refractometers. Status and shortcomings of direct and remote sensing techniques for measurement of atmospheric refractivity are also discussed.     

Estimation of radio refractivity structure using matched-fieldarray processing

In coastal regions the presence of the marine boundary layer can significantly affect RF propagation. The relatively high specific humidity of the underlying “marine layer” creates elevated trapping layers in the radio refractivity structure. While direct sensing techniques provide good data, they are limited in their temporal and spatial scope. There is a need for assessing the three-dimensional (3-D) time-varying refractivity structure. Previously published results indicate that matched-field processing methods hold promise for remotely sensing the refractive profile structure between an emitter and receive array. This paper is aimed at precisely quantifying the performance one can expect with matched-field processing methods for remote sensing of the refractivity structure using signal strength measurements from a single emitter to an array of radio receivers. The performance is determined via simulation and is evaluated as a function of: (1) the aperture of the receive array; (2) the refractivity profile model; and (3) the objective function used in the optimization. Refractivity profile estimation results are provided for a surface-based duct example, an elevated duct example, and a sequence of time-varying refractivity profiles. The refractivity profiles used were based on radiosonde measurements collected off the coast of southern California     

Theoretical performance limits on tropospheric refractivityestimation using point-to-point microwave measurements

Ducted propagation above the ocean surface can seriously impact shipboard radar and communications. Point-to-point microwave measurements have been proposed as a means of estimating tropospheric refractivity for the purposes of characterizing surface-based ducts. This paper addresses the theoretical performance of refractivity estimates that can be made by combining field measurements at different frequencies with prior statistics of refractivity variation. Parameterizing the refractivity profile using empirical orthogonal functions derived from a historical database, both Cramer-Rao performance bounds and the maximum a posteriori (MAP) estimate are discussed using coherent or incoherent signals. Results obtained using a realistic model of refractivity conditions off Southern California suggest that multifrequency propagation measurements can significantly improve the estimation of refractivity and propagation loss profiles     

海面大气环境下雷达作用距离的预报方法

研究了海洋大气环境条件下雷达对已知散射截面积目标作用距离的预报方法。通过气象信息得到大气折射率剖面,利用抛物型方程计算出电磁波传播单程损耗,利用雷达方程得到目标的传播损耗门限,最后得到雷达对目标的最远作用距离。实测结果表明,此方法是可行的。     

蒸发波导折射率剖面数据采集系统设计

计算估计蒸发波导折射率剖面是雷达部队比较关注的问题。本文设计的海上蒸发波导折射率剖面数据采集系统采用小火箭发射技术和单片机、传感器与无线数据传输技术,克服了现有的探空气球等系统的缺点,为海上蒸发波导折射率剖面估计提供一种更准确实用的方法,以满足研究和作战的需求。     

海洋大气近地层折射指数模式及其在蒸发波导分析上的应用

利用Ｍｏｎｉｎ－Ｏｂｕｋｈｏｖ相似理论给出了不同大气结条件下海洋大气近地层折射指数模式，并利用这些模式分析了蒸发波导内可能存在的波导模，给出了确定蒸发波导所能捕获最大电磁波波长及相应最低频率的计算式并对其在不同大气层结条件下的计算结果进行了比较，发现在不稳定、中性和近中性层结条件下，其计算结果比较接近，但在强稳定层结条件下，差异显著，最后给出了射线追踪方程，并通过用多层线性模式来近似蒸发波导内大气     

纯转动拉曼激光雷达反演低层大气折射率廓线

大气折射率是影响光电探测领域测量精度的重要因素.为了提高光电测量精度,提出利用纯转动拉曼激光雷达信号反演低层大气折射率廓线的方法.通过接收N2和O2的纯转动拉曼回波信号,由双光栅单色仪分光后获得高低量子信号.根据高低量子信号的比值反演得出大气温度和大气压强廓线,从而获得大气折射指数垂直分布.通过与折射指数理论模型相比较,表明纯转动拉曼激光雷达反演对流层折射指数有较高的精度.给出了多组折射指数廓线的反演结果,得出多天夜晚不同时刻折射指数的特性.结果表明一天中不同时刻折射指数变化较小,7.5 km内最大相对误差约为0.4%;不同月份之间折射指数波动较为明显,4.5 km内相对误差可达3.5%左右.     

Stratified refractivity effects on microwave propagation near the earth's surface

The effects on microwave radar performance of a horizontally stratified refractive index within the first 8 m of the earth's surface are considered. The radar propagation paths examined are near horizontal and about 1 km in length. The effects of several assumed refractivity profiles on the antenna pattern and on the interference produced by ground reflection are shown. Field test results compare the predicted radar performance obtained from a knowledge of the refractivity profile with the observed performance.