Wingtip generated wake vortices as radar target

Previous radar wake vortex detection experiments have resulted in measured beam averaged values of radar reflectivity from wake vortices in clear air. We have employed average wind and thermodynamic variable output from a two dimensional wake vortex model in clear air and fog to predict radar reflectivity in a wake vortex on a one meter grid. The results agree well, compared to data in the literature. In the clear air case, scales of turbulence were analyzed at each grid point to determine the appropriate maximum radar frequency for detection, initial wake structure, transport, and vortex persistence are related to atmospheric winds, atmospheric stability, and generating aircraft characteristics     

Spiky sea clutter at high range resolutions and very low grazingangles

X-band (9.5-10.0 GHz) backscatter at near grazing incidence (0.2 deg) from the sea off the coast of Kauai, Hawaii, was measured with a radar characterized by a high spatial resolution in range (0.3 m) and a high temporal resolution (2000 Hz pulse repetition frequency (PRF)). Extensive amounts (over 20 min per measurement) of vertically and horizontally polarized sea clutter data were taken with upwind (UP) and crosswind (CR) transmit geometries during the collection campaign. Specific but representative examples of the clutter were statistically and phenomenologically analyzed over time scales varying from long (200 s), to intermediate (5 s), to short (50 ms), and over range swaths varying from full (160 m), to partial (30 m), to a single range cell (0.3 m). All analyses and results presented here are noncoherent, involving only the clutter amplitudes. Each type of clutter exhibited the characteristic spiky behavior which has come to be expected from microwave sea backscatter observed at low grazing angles and high range resolutions, while showing, between themselves, marked transmit geometry and polarization dependent contrasts, with the horizontally polarized clutter, measured with an UP transmit geometry, being especially notable for its frequently occurring, significant high frequency spectral content. Within the same clutter type, differences were observed in the probability distributions of radar cross sections (RCS) of spatially and temporally extended spiking events     

某复杂构型导弹高速风洞部件测力实验研究

在2m×2m超声速风洞开展了某复杂构型导弹部件测力实验研究,实验的迎角范围为-6°~10°,侧滑角范围为-6°~6°,测力部件包括保护罩、左侧翼、大整流罩和小整流罩等部件。使用五分量天平对保护罩在风洞实验中所受到的载荷进行了测量,并利用分断面缝隙处的压力测量结果对保护罩测力实验结果进行了修正,获得了保护罩在实验条件下的真实部件气动特性数据;使用3台三分量天平,直接获得了左侧翼、大整流罩和小整流罩在实验条件下的部件气动特性数据。研究结果表明：实验结果可以作为结构设计的依据;保护罩测力实验结果修正方法合理可行,能够为今后类似部件测力实验结果的修正提供借鉴。     

Effects of polarization and resolution on SAR ATR

Lincoln Laboratory is investigating the detection and classification of stationary ground targets using high resolution, fully polarimetric, synthetic aperture radar (SAR) imagery. A study is summarized in which data collected by the Lincoln Laboratory 33 GHz SAR were used to perform a comprehensive comparison of automatic target recognition (ATR) performance for several polarization/resolution combinations. The Lincoln Laboratory baseline ATR algorithm suite was used, and was optimized for each polarization/resolution case. Both the HH polarization alone and the optimal combination of HH, HV, and VV were evaluated; the resolutions evaluated were 1 ft/spl times/1 ft and 1 m/spl times/1 m. The data set used for this study contained approximately 74 km/sup 2/ of clutter (56 km/sup 2/ of mixed clutter plus 18 km/sup 2/ of highly cultural clutter) and 136 tactical target images (divided equally between tanks and howitzers).     

基于激光吸收光谱层析技术的超燃冲压发动机氢气引导煤油燃烧过程分析

为了解超燃冲压发动机引导点火过程中燃烧流场截面参数分布特征和传播规律,利用激光吸收光谱技术对氢气引导煤油燃烧过程进行测量和分析.在约200ms的引导燃烧过程中,激光吸收光谱层析测量系统对流场截面温度二维分布进行了全程的测量,时间分辨率为1ms.对于测量结果,重点分析了氢气加注、上壁面煤油加注和下壁面煤油加注三个关键阶段...     

In-orbit demonstration of rendezvous laser radar for unmanned autonomous rendezvous docking

The National Space Development Agency of Japan (NASDA) performed unmanned autonomous rendezvous docking (RVD) experiments using the Engineering Test Satellite VII (ETS-VII) in 1998 and 1999. In these experiments, a rendezvous laser radar (RVR) was used as the primary navigation sensor during the final approach phase (relative distances from 500 m to 2 m). The RVR functioned properly, and its characteristics, which are measurement accuracy, optical propagation, and acquisition/tracking, satisfied the requirements. The experimental results show that RVR is effective for autonomous rendezvous docking.     

周期性供油气助雾化直喷喷嘴雾化特性试验

对一种典型的周期性供油气助雾化直喷喷嘴的雾化特性进行试验研究,分析总结了喷油脉宽、间隔时间、喷气脉宽以及空气压力对雾化性能的影响规律.试验中使用RP-3航空煤油作用工质,使用压缩空气作为介质;用激光粒度分析仪对油雾场进行测量并进行处理分析;喷油脉宽与喷气脉宽变化范围为2～8ms,间隔时间为-2～5ms,空气压力为0.1～0.65MPa.研究结果表明:随着气油比的增加,索太尔平均直径减小,均匀程度增加,雾化性能提高;增加空气压力,可以使空气密度增加,加大空气与燃油的气动作用力,有利于雾化性能的提高;增加间隔时间也可使雾化性能有小幅度的提升;在较大的平均粒径下,更加分散的粒径分布仍然可以具有较大的均匀度分布指数.对试验数据进行分析,在较高空气压力下,得到了该周期性供油气助雾化直喷喷嘴的平均粒径的经验计算模型.      

雾化激波管研制和煤油点火延时测量

为测量雾化煤油点火延时和得到火焰自发辐射光强分布,研制了雾化激波管和燃料雾化、进气系统。采用“管外预混”思想形成煤油气溶胶,通过连续进气和抽吸方法使气溶胶均匀分布,未出现明显的液滴沉降和壁面吸附。当点火温度为1000K,缝合接触面运行的实验时间大于10ms。由压电传感器PCB和光电倍增管PMT测量指定点压力、OH基光强时间曲线。利用Mie散射测量煤油气溶胶散射光分布,采用ICCD拍摄自点火发射光强。结果表明：该雾化系统可形成粒径为2～5μm煤油气溶胶。当压力为0．1MPa、温度为1300K～1700K,测得化学计量比≠=1．0煤油气溶胶点火延时τig为0．07—6ms,In（τig）和10000／τig近似呈线性关系。与气态煤油相比,该文高温点火延时和已有文献数据接近,但低温点火延时偏大,表明了低温下煤油点火的两相效应。     

VSAR: a high resolution radar system for ocean imaging

The velocity synthetic aperture radar (VSAR) is a conceptual synthetic aperture radar (SAR)-based sensor system for high resolution ocean imaging. The VSAR utilizes data collected by a multielement SAR system, to extract information not only about the radar reflectivity of the observed area, but also about the radial velocity of the scatterers in each pixel. This is accomplished by making use of the phase information contained in multiple SAR images, and not just the magnitude information as in conventional SAR. Using this velocity information, the VSAR attempts to compensate for the velocity distortion inherent in conventional SAR and to reconstruct the ocean reflectivity. We present the basic theory of the VSAR system and its performance. We also provide an analysis of the VSAR imaging mechanism for a statistical model of the radar returns, designed to capture the effects of speckle and of resolution degradation due to the decorrelation of the radar returns     

基于广义Kalman估计的机载雷达高精度控制系统

 研究了在某型现役机载雷达系统中, 采用广义Kalman 滤波器方法来预估目标机的俯仰角和方位角,产生跟踪目标用的雷达天线驱动信号, 替代传统的速率陀螺测量元件来补偿本机机动所造成的扰动的方法,同时对探测信号本身所具有的延迟起到了补偿作用。对目标的运动采用直角坐标系中的Singer 模型描述, 而对测量信号则是应用极坐标系中的描述, 采用广义Kalman 滤波器来完成估计, 即在每一步的估计和控制中对计算测量方程进行线性化结果, 实现两种坐标系的转换。通过应用Matlab/ Simulink 软件对整个系统的建模、设计及仿真研究, 得到了满意的结果。     

The ELDORA/ASTRAIA airborne Doppler weather radar: results fromrecent field tests

The ELDORA/ASTRAIA airborne Doppler weather radar was recently placed in service by US and French atmospheric sciences research laboratories. The ELDORA/ASTRAIA radar is designed to provide high resolution measurements of the air motion and rainfall characteristics of atmospheric storms which are too large, remote or fast-moving to be adequately observed by ground-based radars. This paper discusses the measurement requirements and the design goals of the radar and presents sample measurements from a recent weather research field program     

两电极等离子体高能合成射流流场及其冲量实验研究

两电极等离子体高能合成射流激励器通过腔体内电极间的瞬时电弧放电加热腔内气体,在激励器出口产生压差并喷出高速射流,从而产生反作用力和冲量。针对两电极等离子体高能合成射流响应快、持续时间短的特点,设计了单丝扭摆式微冲量测量系统,并结合高速阴影系统,对两电极等离子体高能合成射流的流场发展过程及其单脉冲冲量特性进行了实验研究。实验结果表明,两电极等离子体高能合成射流响应时间小于10μs,射流持续时间约为1ms,射流前锋最大速度约为190m/s,射流流场发展过程中存在多道强压缩波,并以当地声速向下游传播。单丝扭摆式微冲量测量系统可实现μN·s量级冲量测量精度,单脉冲冲量约为32μN·s,并且在低频状态下射流总冲量随激励器放电频率成线性增加。     

Synthetic aperture radar image formation from compressed data usinga new computation technique

A convolution technique is proposed that allows direct reconstruction of the processed synthetic-aperture radar (SAR) image from the digitally-sampled, block-encoded raw data. This computational compression technique reduces the number of arithmetic operations from that required by fast Fourier transform (FFT) convolution for SAR processing. SAR phase histories are block encoded and directly processed into an image where only arithmetic additions are required for the processing. For SAR data previously block encoded, the processing time is reduced by a factor of 100 or more. A speed-up of three times over SAR processing by FET convolution has been demonstrated when both computation of the block encoding and subsequent direct processing are included in the time. SAR image quality measurements for a method of block encoding called vector quantization at compression ration ranging from 5:1 to 50:1 show image degradation proportional to the compression ratio. For a 5:1 compression radio, image quality measurements show minimal degradation     

典型雷达信号对瞬时测频接收机的影响

瞬时测频接收机通常工作在复杂的电磁环境中,宽带的接收特性使其极易受到影响。针对瞬时测频接收机的工作机理,选取了连续波信号、高占空比信号、同时到达信号、低截获概率雷达信号等典型雷达信号样式,对瞬时测频接收机产生的影响,分析引起工作性能下降的原因和现象,并对部分结论进行了仿真实验验证,得到了与分析结论一致的实验结果。对雷达侦察装备研制和使用具有一定的借鉴意义。     

Aerodynamic force and moment measurement of 10° half-angle cone in JF12 shock tunnel

An aerodynamic force and moment measurement was conducted in JF12 long-testduration detonation-driven shock tunnel of Institute of Mechanics,Chinese Academy of Sciences.The test duration of JF12 is 100–130 ms.The nominal Mach number is 7.0 and the exit diameter of the contoured nozzle is 2.5 m.The total enthalpy is 2.5 MJ/kg which duplicates the hypersonic flight conditions of Mach number 7.0 at 35 km altitude.The test model is the standard aerodynamic force model of 10° half-angle sharp cone.The length of the test model is 1500 mm and the weight is 57 kg.The aerodynamic forces were measured with a six-component strain balance.The angles of attack were set to be à5°,0°,5°,10° and 14°,respectively.The experimental results show that in the 100–130 ms test duration,the signals of strain balance have 3–4 complete vibration cycles.So,the aerodynamic forces and moments can be obtained directly by averaging the signals of balance without acceleration compensation.The force measurement error of repeatability of JF12 is less than 2%.The aerodynamic force coefficients of JF12 are in good agreement with those of conventional hypersonic wind tunnels.For this test model at Mach number 7.0 and total enthalpy of 2.5 MJ/kg,the real-gas effects on aerodynamic force characteristics are not very evident.     

On scheduling a multifunction radar

Among several other tasks, the radar of a fighter has to search, track and identify potential targets. The waveforms used by the radar for each of these tasks are most often incompatible and hence, cannot be processed simultaneously. Moreover, these tasks are repeated several times in a cyclic fashion. Altogether, this defines a complex scheduling problem that impacts a lot on the quality of the radar's output. In this paper, we define a formal framework for this real time scheduling problem and we introduce several techniques to compute efficient schedules for the radar. Experimental results are provided.     

A mean track approach applied to the multidimensional assignment problem

The primary contribution of this paper is the introduction of a new preprocessing method to eliminate unlikely observation-to-track pairs with medium size target-measurement spacings before filter gating is carried out. The proposed method follows a track-oriented approach, with the different track hypotheses being contained in target trees. A mean track is computed for each target tree to capture as much variability as possible from the track hypotheses which are in the tree. Each newly received measurement is first gated with the mean track; only if the outcome of the test is positive, the measurement is gated with all the track hypotheses in the tree. The experimental results support the theoretical claims in the paper and show that a significant reduction in the number of observation-to-tracking pairing tests is achieved.     

Distance estimation at 60 GHz

An FM-CW radar front-end was fabricated in an integrated manner at 60 GHz by using the NRD guide. Main emphasis was placed on compactness in size and high-precise operation in performance. The fabricated radar consists of an FM Gunn oscillator, a balanced mixer, and a planar antenna fed by leaky NRD guide with a mechanically beam-scanning performance. All circuit components and the antenna were contained in a compact housing of 170 /spl times/ 140 mm in area and 25 mm in thickness, and thus, a thin type of millimeter-wave radar front-end was successfully developed. Moreover, an error of distance estimation was measured to be less than a distance of 0.7 m.     

Correlation between horizontal and vertical monopulse measurements

Many radar systems use the monopulse ratio to extract angle of arrival (AOA) measurements in both azimuth and elevation angles. The accuracies of each such measurement are reasonably well known: each measurement is, conditioned on the sum-signal return, Gaussian-distributed with calculable bias (relative to the true AOA), and variance. However, we note that the two monopulse ratios are functions of basic radar measurements that are not entirely independent, specifically in that the sum signal is common to both. The effect of this is that the monopulse ratios are dependent, and a simple explicit expression is given for their correlation; this is of considerable interest when the measurements are supplied to a tracking algorithm that requires a measurement covariance matrix. The system performance improvement when this is taken into account is quantified: while it makes little difference for a tracking radar with small pointing errors, there are more substantial gains when a target is allowed to stray within the beam, as with a rotating (track-while-scan) radar or when a single radar dwell interrogates two or more targets at different ranges. But in any case, the correct covariance expression is so simple that there is little reason not to use it. We additionally derive the Cramer-Rao lower bound (CRLB) on joint azimuth/elevation angle estimation and discover that it differs only slightly from the covariance matrix corresponding to the individual monopulse ratios. Hence, using the individual monopulse ratios and their simple joint accuracy expression is an adequate and quick approximation of the optimal maximum likelihood procedure for single resolved targets.