一种低空突防中的雷达探测盲区预测方法

为了提高低空突防中雷达探测盲区预测的可靠性,提出了一种雷达探测盲区预测方法。该方法在分析雷达探测性能的基础上,基于数字地图抽取地形剖面,采用抛物方程法计算电波在空间的传播损耗,根据雷达探测门限预测某高度平面上的雷达探测盲区。仿真结果表明,该方法能够有效预测复杂环境下的雷达探测盲区,提高飞行器低空突防的成功概率。     

岸基雷达的大气波导特性及其影响分析

对于低空探测的岸基雷达,希望能尽早准确判知低空威胁目标,但在出现大气波导效应时,雷达探测性能往往会受其影响。从大气波导效应的成因、类型以及传播条件出发,分析了大气波导效应对岸基雷达正常工作的影响,初步提出了在大气波导情况下改善和提高岸基雷达低空检测性能的技术措施。     

提高雷达低空探测能力的措施研究

针对未来战争的作战系统应采用多种探测手段相结合,以形成较为完善的低空防御能力的问题。文中分析了影响雷达低空探测性能的主要因素,并针对各因素提出了改善雷达低空探测性能的各项措施,如减少地球曲率影响、减少多路径效应影响的措施,采用各种新技术和多探测手段有机组合,以提高雷达低空探测性能的方法,并通过功能互补的方式,形成了较为完善的低空防御能力。     

电子干扰掩护下隐身飞机低空突防战术仿真分析

为研究电子干扰掩护条件下隐身飞机低空、超低空突防战术作战效能，基于某典型隐身飞机动态雷达散射截面（radar cross section, RCS）和地面对电磁波的反射效应，研究了低空突防战术对雷达探测性能的影响.首先，采用坐标转换矩阵计算不同时刻雷达照射飞机角度，通过高频近似算法计算突防过程中飞机的动态RCS序列；其次，引入雷达和干扰机天线方向图传播因子F和Fj，表征地面对电磁波的反射效应，推导雷达方程，得到雷达探测距离和探测概率；最后，针对构建的隐身飞机突防场景，通过计算机进行仿真，分析飞行高度、地面起伏等参数变化对雷达探测性能的影响.仿真结果表明，在电子干扰掩护下，利用隐身飞机在鼻锥方向的低可探测性能，采用低空、超低空突防战术能显著降低雷达对隐身飞机的探测性能，而地面反射效应对雷达探测性能具有明显影响.研究结果可为作战训练中灵活运用该战术提供理论参考.     

海洋大气波导对雷达探测性能影响的研究

建立了海洋环境中典型波导的经验模型,用电磁波传播的地型抛物方程以及分步傅里叶算法对电磁波在各种波导情况下的传播衰减情况进行了数值模拟,并构建了雷达性能评估模型,应用该方法评估了不同波导环境下雷达的探测性能,分析了由于大气波导环境的影响所产生的雷达低空异常探测特征。     

雷达网低空探测能力评估方法

针对雷达网反低空、超低空突防的低空探测能力评估的需求,在综合分析雷达网低空探测威力和地形、地物影响的基础上,提出了一种基于数字地图的雷达网低空探测能力评估方法,即运用各高度层飞机的飞行区域面积和雷达网的飞行区域探测面积进行综合性的定量描述,最后进行了程序设计并给出了仿真结果。     

基于雷达高度表信号的低空目标检测技术

针对低空目标突袭的威胁,根据低空目标普遍携带雷达高度表的特征,提出了基于雷达高度表信号探测的低空目标检测技术。针对海面飞行环境,根据双基地雷达的原理,对海面雷达散射信号进行了理论计算,从功率角度对低空目标检测可行性进行了分析,并给出了将侦察系统升空探测低空目标所携雷达高度表信号的方法,达到了对低空突防目标预警探测的要求。     

表面波导对雷达低空探测误差影响的研究

电磁波在海洋大气环境中传播,受表面波导这种异常现象的影响常常呈现出复杂的折射特征,这对雷达定位的精确性具有重要影响,针对这一问题,文中建立了表面波导环境下电磁波传播真实轨迹的精确算法,利用仿真手段研究了表面波导对雷达低空探测(仰角<5°)误差的影响,仿真结果表明,表面波导环境下电磁波出现“陷获”传播时,射线的真实轨迹明显偏离视在轨迹,形成了雷达低空探测时极明显的异常高度误差和仰角误差。     

雷达的低空探测威力

讨论了影响雷达低空探测威力的一些因素，介绍了计算雷达低空探测威力的方法，并提出了提高雷达低空探测性能的措施。     

太赫兹频段的近程ISAR成像系统

介绍了一种THz频段的近程逆向合成孔径雷达(ISAR)成像系统.该系统采用EIO作为THz功率源,工作频率345 GHz,探测距离5～20 km,探测精度可达3.75 m,并具有较小的波束宽度、较高的分辨率和突出的抗干扰能力.在此基础上,对ISAR成像系统的技术指标进行分析.包括天线增益与探测距离和雷达发射功率之间的关系.该近程ISAR成像系统,可以进一步改进低空目标探测技术,未来随着太赫兹技术的发展,将会在低空探测和近程反导方面得到广泛应用.     

Limitations on oceanographic use of beam-limited target-referenced radars

A general development is undertaken to determine the limitations on the use of beam-limited target-referenced radars in the measurement of ocean wave height. This class of radars is concerned only with the range extent of the target, not the range to the target. The nonzero range extent of a flat waveless sea and the compounding effect of pointing errors due to radar platform instability cause difficulty in measuring low wave heights and impose a maximum operating altitude on such systems. It is seen that it is impractical to obtain accurate measurements for wave heights of interest at altitudes above those used by commercial aircraft (10 000 m). Additionally, the typical ratio of dominant wavelength to significant wave height (SWH) of 30 for wind-driven gravity waves imposes an upper limit on the (SWH) measurable for a given altitude and beamwidth.     

The impact of satellite altitude on the performance of LEOS based communication systems

Low earth orbit satellite (LEOS) systems promise to provide global communication, including voice and data services from Iridium and high capacity broadband services from Teledesic. In design of LEOS systems, the choice of satellite altitude is an important consideration, which has a significant impact on system performance. Among the factors affected by satellite altitude choice are system capacity, user‐to‐user delay, power system design and communication services that can be offered. This paper analyzes the effects of satellite altitude on quality of service, frequency reusability and power system sizing. It is found that a choice of low altitude has a positive impact on system capacity and power system requirements. As a consequence, satellite mass and launch cost can be reduced for satellites in lower orbits due to the lower power requirements. In terms of user‐to‐user delay, the results are in favor of medium altitudes, while very high altitudes are not a good choice relative to these measures. This revised version was published online in June 2006 with corrections to the Cover Date.     

Mobile P-service satellite system comparison

Several future operators of the mobile handheld telephone (P-service) satellite communications systems are gearing up for system implementation to compete for the mobile handheld telephone market of the future. While these companies are proceeding with system realization, they are also looking for partners to finance these huge satellite projects. Potential partners or bulk users are administrations of national communication systems and operators of national communication satellites. These future partners ask themselves which P-service satellite communication system they should choose. There is not an easy answer because P-service satellite systems come in many varieties. There are the low altitude earth orbiting satellites (LEOs), the medium altitude earth orbiting satellites (MEOs), and the geosynchronous altitude earth orbiting satellites (GEOs). Each system has a different type of satellite repeater: digital regenerative, transparent digital, and the bent-pipe. And each satellite system uses its own modulation/multiple access system. The fact that satellites circle the earth at different altitudes has an impact on speech quality, and, because systems vary in satellite as well as constellation complexity, there are different price tags attached. All systems display ingenious features and will eventually work. Mobile users will decide which system will best serve their purposes. This article attempts to compare six P-service satellite systems and find a method for system selection. By use of self-established system criteria, it is possible to arrive at a P-service system selection. By weighing the system criteria, the sensitivity of system selection can be tested. The results or the selection of a particular system should not be considered a recommendation; rather, the process of selection should be used as a possible guideline.     

基于调频广播的单站无源定位系统的威力估计

基于调频广播的单站无源定位系统实际相当于收发分置的双基雷达,其直达波和地杂波的传播为小擦地角的低空传播,且影响威力范围的因素随基线长度的变化而有所不同.本文考虑低空传播,分析了不同基线长度时影响观测范围的主要因素,推导了对应情况下对高空飞行目标的观测面积的计算公式.结合上述公式以及对参考天线的要求可以得到最优的基线距离.仿真实验验证了上述的分析,并指出降低收发天线的高度可以进一步提高观测面积.     

中高层大气临边红外辐射的LTE与non-LTE模拟对比

利用战略高空辐亮度代码(Strategic high-altitude radiance code, SHARC) 和通用大气辐射传输代码 (Combined atmospheric radiative transfer, CART) 模拟分析中高层大气临边红外辐射的算法适用范围。 通过模拟结果的对比,初步验证了CART临边模式的有效性。模拟结果表明,在主要的红外波段上,至少45 km以 下的平流层区域内临边红外辐亮度的计算都可以采取局域热力学平衡模式(Local thermodynamics equilibrium, LTE);不同的红外波段在不同的大气条件下,需要采用非局域热力学平衡模式 (Non-local thermodynamics equilibrium, non-LTE)的高度不同,其中15 $\mu$m波段在至少80 km的切点 高度以下都可以使用LTE模式模拟,但是对于CO$_2$ 4.3 $\mu$m带主导的3$\sim$5 $\mu$m波段和O$_3$ 9.6 $\mu$m带 主导的8$\sim$12 $\mu$m波段,在中间层的多数区域内就必须采用non-LTE模式。     

EMI／EMC／EME以及测试（续4）

冷却的损失 电子系统依靠冷却来阻止过热引起的性能降低或失效。这些系统被设计工作在某种环境和气流条件下，由外部源吸收的热量会造成问题。温度条件可以降低元件和电路的性能。如问题1的例子，电源滤波器的元件值会在某些温度或高度下改变。这些改变会使正常工作环境下的滤波器的效率降低，因此电源线的噪声不再被有效地衰减。外部的射频干扰会打断设备的正常工作。     

瑞利-拉曼散射激光雷达探测大气温度分布

介绍一台用于夜晚探测大气温度分布的L625瑞利-拉曼(Rayleigh-Raman)散射激光雷达。采用Nd：YAG激光器三倍频输出355nm作为发射激光，利用弱光子计数技术检测大气中分子的瑞利散射和N2分子振动拉曼散射回波，分析得到了平流层和对流层中上部大气温度的垂直分布廓线。其观测结果分别与HALOE／UARS卫星和无线电气象探空仪结果进行了对比分析。其中，激光雷达观测的平流层温度与HALOE卫星的结果对比表明，它们在高度25～65km内显示出较好的一致性，20个夜晚的平均温度差别基本上小于2K。激光雷达与无线电气象探空仪探测的对流层温度在高度为5～18km内反映了较为一致的分布趋势，15个夜晚的平均温度差别在6～16．5km高度内小于3K。这些结果表明，L625瑞利-拉曼散射激光雷达观测数据可靠，可用于大气温度分布的常规观测和分析研究。     

A global message network employing low Earth-orbiting satellites

A global message communication network for low-density traffic, using satellites at low altitudes, is described. This network affords around-the-clock service to any part of the globe, including the polar regions. Such a network can accommodate static and mobile user terminals simultaneously. The oblate globe is modeled as a regular polyhedron with 12 facets for setting up the orbits. Satellites are positioned uniformly in low-altitude symmetrical orbits. The symmetrical orbits are those whose axes are symmetrical in the three-dimensional space. The authors study the coverage aspects of the 6-orbit scheme and the 10-orbit scheme, each with satellites deployed at an altitude of 5000 km. At this altitude, the terrestrial user terminals can access satellites at a grazing angle of 45°. The method of access over the crosslinks is the slotted ALOHA scheme. For low-density traffic, the downlink and uplink throughput rates are estimated. Simulation results agree with these analytical estimates for low values of network offered load     

安徽省分钟降雨率分布特征

利用安徽省2017—2019年81个国家级气象站实测分钟降雨率资料，统计站点分钟降雨率累积分布，对安徽省分钟降雨率的时空分布特征进行分析，并将实测降雨率与ITU降雨率模型预测结果进行对比.结果表明:安徽省山区的分钟降雨率累积分布整体上高于其他地区，淮北平原东部在小于0.03%时间概率点时呈现出较高分钟降雨率累积分布；山区受地形降雨影响，高海拔处分钟降雨率总体上高于低海拔处；平原地区的R（0.01）年际变化较其他地区显著；2017年、2018年和2019年的降雨最坏月份分别为8月、7月和6月.实测分钟降雨率分布与ITU模型预测结果总体上保持一致，在0.03%时间概率点以内，模型预测结果整体偏低；在淮北平原和山区高海拔处，模型预测结果误差较大.     

用瑞利散射激光雷达探测平流层中上部温度

介绍了一台用于平流层中上部温度探测的双波长激光雷达 ,分析了数据处理方法及其过程。该激光雷达获得的结果与NOAA NMC及MSISE 90模式资料对比表明 ,在 30～ 40km高度范围内三者反映了较一致的温度分布特征。一般情况下 30～ 40km范围内它们的温度偏差小于 3K ;低层 30km以下很可能主要受气溶胶的影响 ,相对偏差小于 6K。