水泥路面激光散射特性研究

为了通过激光散射特性识别不同粗糙程度水泥路面,设计了路面粗糙度测量系统.使用千分表测量水泥路面高度分布,计算高度均方根与相关长度.根据以上参量采用功率谱频域滤波生成随机粗糙表面以模拟水泥路面,通过切平面近似将粗糙面离散为大量微面元,由菲涅耳公式计算本地场,利用蒙特卡罗方法获取不同偏振光入射条件下粗糙面双向与后向散射光强...     

A Parameterization of the Effect of Surface Roughness on Microwave Emission

A simple model is developed to represent the net effect of surface roughness on the microwave emission from soils. The reflectivity of a rough soil surface is defined in a theoretical model that includes both coherent and incoherent reflectivities in terms of the statistical properties of the rough surface, i.e., the surface height standard deviation ? and its horizontal correlation length l. It is shown that the rough surface reflectivity obtained from this theoretical model can be presented in a form that is simply the reflectivity Ro of a smooth surface attenuated by a "rough thickness" G. It is found that the rough thickness G can be parameterized as a function of the statistical slope ratio m (=?/l) of a rough surface by a simple power-law relationship. Since the slope of a rough surface can be determined experimentally, the rough thickness G can be quantitatively estimated from the parametric representation. Model calculations show that this simple model can provide reasonably accurate results of predicted brightness temperatures that agree well with field measurements within experimental uncertainty.     

Experimental study of propagation characteristics on roads on asnowy mountain

Experimental results of radio propagation characteristics on roads on snowy or snow-capped mountains are discussed. Propagation tests were carried out on the horizontal and vertical polarization characteristics in a frequency range from VHF to X-band (150 MHz to 4.7 GHz). Field strengths along the road and field distributions in the cross section were measured. The attenuation constants in a straight-road section were obtained by the least-squares method using measured data. It is shown that the attenuation constants are experimentally minimum in a frequency range of 1-3 GHz for each polarization, and that field strengths in the cross section are close to cosine distribution in the horizontal direction, and in the vertical direction increase nearly monotonically with increasing elevation     

Polarimetric characterization of debris and faults in the highwayenvironment at millimeter-wave frequencies

In this paper, measurements and models for the polarimetric backscatter response of various paint targets on roads and road surface faults are presented. Of particular interest are debris and faults that could lead to fatal accidents and damage of property. A desired safety feature for automotive radar sensors is the capability of detecting such debris and faults. The detectability of a point target is evaluated by comparing its RCS value with the RCS threshold value defined by the backscatter response of the road surface. Extensive backscatter measurements at W-band were conducted to obtain the backscatter response of typical debris and faults on asphalt surfaces at near grazing incidence angles (76°-86°). On the other hand, theoretical models, based on diffraction from impedance wedges and scattering from impedance cylinders, respectively, as well as physical optics approximation, were developed to predict the backscatter response of road surface faults and targets with planar facets on road surfaces. Experimental results indicate that detectability in all cases is a function of target size, its azimuthal angle with respect to radar boresight, and the polarization state of the system. The measured backscatter response is used to verify the validity of the theoretical models. Angular polarimetric backscatter measurements of targets defining roadside boundaries such as a concrete curb, a guardrail, and a pebble surface are also presented. The results of these measurements could be used to alert fatigued drivers should their vehicles be heading sideward     

Propagation factors controlling mean field strength on urban streets

Calculation of mean field strength for urban mobile radio has been made on a ray-theoretical basis assuming an ideal city structure with uniform building heights. The result shows that building height, street width, and street orientation as well as mobile station antenna height are controlling propagation parameters in addition to the ordinary factors. The major theoretical characteristics agree approximately with experimental data including conventional empirical predictions. This suggests a way of theoretically predicting mean field strength in an urban area.     

A comparison of theoretical and empirical reflection coefficientsfor typical exterior wall surfaces in a mobile radio environment

This paper presents microwave reflection coefficient measurements at 1.9 GHz and 4.0 GHz for a variety of typical smooth and rough exterior building surfaces. The measured test surfaces include walls composed of limestone blocks, glass, and brick. Reflection coefficients were measured by resolving individual reflected signal components temporally and spatially, using a spread-spectrum sliding correlation system with directional antennas. Measured reflection coefficients are compared to theoretical Fresnel reflection coefficients, applying Gaussian rough surface scattering corrections where applicable. Comparisons of theoretical calculations and measured test cases reveal that Fresnel reflection coefficients adequately predict the reflective properties of the glass and brick wall surfaces. The rough limestone block wall reflection measurements are shown to be bounded by the predictions using the Fresnel reflection coefficients for a smooth surface and the modified reflection coefficients using the Gaussian rough surface correction factors. A simple, but effective, reflection model for rough surfaces is proposed, which is in good agreement with propagation measurements at 1.9 GHz and 4 GHz for both vertical and horizontal antenna polarizations. These reflection coefficient models can be directly applied to the estimation of multipath signal strength in ray tracing algorithms for propagation prediction     

大粗糙度表面激光散射特性实验研究

本文利用激光散射自动测量系统,对经喷丸处理后的钢基粗糙表面及其喷漆表面的后向激光雷达散射截面(LRCS)进行了测量。测量波长分别为λ=633nm和λ=904nm.在λ=904nm,利用粗糙面电磁散射理论的基尔霍夫方法对上述样片进行了理论计算,其中将粗糙表面视为双尺度模型,根据驻留相位法和标量近似法理论计算双尺度模型随机粗糙表面的散射强度角分布,其理论值与实验测量结果有较好的吻合。     

Electromagnetic scattering interaction between a dielectriccylinder and a slightly rough surface

An electromagnetic scattering solution for the interaction between a dielectric cylinder and a slightly rough surface is presented in this paper. Taking the advantage of a newly developed technique that utilizes the reciprocity theorem, the difficulty in formulating the secondary scattered fields from the composite target reduces to the evaluation of integrals involving the scattered fields from the cylinder and polarization currents of the rough surface induced by a plane wave. Basically, only the current distribution of isolated scatterers are needed to evaluate the interaction in the far-field region. The scattered field from the cylinder is evaluated in the near-field region using a stationary phase approximation along the cylinder axis. Also, the expressions for the polarization current induced within the top rough layer of the rough surface derived from the iterative solution of an integral equation are employed in this paper. A sensitivity analysis is performed for determining the dependency of the scattering interaction on the target parameters such as surface root mean square (RMS) height, dielectric constant, cylinder diameter, and length. It is shown that for nearly vertical cylinders, which is of interest for modeling of vegetation, the cross-polarized backscatter is mainly dominated by the scattering interaction between the cylinder and the rough surface. The accuracy of the theoretical formulation is verified by conducting polarimetric backscatter measurements from a lossy dielectric cylinder above a slightly rough surface. Excellent agreement between the theoretical prediction and experimental results is obtained     

Self-limiting MBE growth and characterization of three-dimensionally confined nanostructures on patterned GaAs (311)A substrates

The formation of triangular-shaped dot-like (TD) structures grown by molecular beam epitaxy on GaAs (311)A substrates patterned with square- and triangular-shaped holes is compared. On substrates patterned with square-shaped holes, TD structures are formed via the pinch-off of two symmetrically arranged {111} planes which develop freely in the regions between the holes on the original substrate surface, while the (111)A sidewalls of the as-etched holes develop a rough morphology during growth. The evolution of the rough (111)A sidewalls is eliminated on substrates patterned with triangular shaped holes resulting in similar TD structures with highly improved uniformity over the entire pattern. Spectrally and spatially resolved cathodoluminescence spectroscopy reveals the lateral variation of the quantum-well confinement energy in the TD structures generating distinct lateral energy barriers between the top portion and the nearby smooth regions with efficient radiative recombination. Formation of TD structures provides a new approach to fabricate three-dimensionally confined nanostructures in a controlled manner.     

复杂陆地粗糙面及其上方坦克目标复合散射研究

研究了复杂陆地粗糙面及其上方坦克目标的复合散射特性.基于Monte Carlo方法,利用高斯谱函数模拟不同统计特性的陆地表面,运用加权反正切函数滤波处理以构造边界和连接相邻区域,构建了复杂陆地分区域复合粗糙面的几何模型.提出了一种快速精确求解复杂陆地粗糙面及其上方坦克目标复合散射的混合方法,利用迭代物理光学法求解目标与环境间的多次耦合,运用等效电磁流法修正棱边绕射.分析了复杂陆地粗糙面的散射特性,研究了入射角、均方根高度、相关长度和粗糙面表面结构对复合散射特性的影响.本研究为探测复杂环境上方的坦克目标提供了理论基础,数值仿真结果对雷达目标的探测与识别具有借鉴意义.     

GaN-based light-emitting diode structure with monolithically integrated sidewall deflectors for enhanced surface emission

To improve the overall surface emission efficiency, the structure of a standard GaN light-emitting diode (LED) was modified; the mesa sidewalls were etched at an angle, and deep enough to reach the sapphire substrate. Photoexcitation experiments, including photoluminescence and near- and far-field emission patterns, were performed on LED-like test devices, and results indicated that the angled sidewalls efficiently deflect photons that are initially guided laterally within the GaN epilayer in the off-surface direction. For a sidewall angle of 30/spl deg/, the total surface emission strength was improved by a factor exceeding three. Computer simulations produced results consistent with the experimental observations.     

粗糙海面建模及其在蒸发波导传播中的应用研究

海上蒸发波导微波超视距电波传播对舰载雷达的运行具有重要的影响. 本文基于粗糙海面电波散射特征和海面高度分布概率密度函数,提出了一种考虑海面遮蔽影响的海上电波传播计算方法,并与两种不包含遮蔽影响的粗糙海面建模的计算结果进行了模拟和试验对比. 计算结果为:1）随着计算频率和风速的增大,不同粗糙海面处理方法的计算结果差异增大,对应位置的路径损耗差异可达10 dB;2）基于试验数据的对比初步显示采用考虑遮蔽影响改进的抛物方程模型预测的路径损耗精度相对较高,粗糙海面对电波的遮蔽效应是蒸发波导传播损耗计算中的一个重要因素;3）试验结果为不稳定大气时采用NPS蒸发波导模型、稳定大气时采用PJ蒸发波导模型预测大气折射率剖面,所预测的路径损耗要优于采用单一蒸发波导模型的结果. 本文所得结果对海上电波传播计算和大气波导的反演等具有参考价值.     

典型粗糙表面激光后向散射特性实验

对现有的粗糙度比较样块和其他典型粗糙目标进行了后向光散射特性的实验。实验结果表明,当入射光为632.8 nm波长时,随着入射角的增大,不同的被测目标的散射强度变化得比较明显。如果被测目标的表面斜率均方根比较接近,可以发现它们整体的散射光强度变化趋势几乎一样,而且它们的偏振度也相差不大。表面斜率很小的被测目标,相对其他被测目标,其散射光光强明显大很多,其偏振度也是最大的,说明相对光滑的表面探测到的后向散射光强度比相对粗糙表面探测到的散射光强度大得多。文中关于典型粗糙表面后向散射偏振特性的研究结果对于探讨进行目标识别的理论及应用方面有一定的价值。     

Road extraction from aerial images using a region competition algorithm.

In this paper, we present a user-guided method based on the region competition algorithm to extract roads, and therefore we also provide some clues concerning the placement of the points required by the algorithm. The initial points are analyzed in order to find out whether it is necessary to add more initial points, and this process will be based on image information. Not only is the algorithm able to obtain the road centerline, but it also recovers the road sides. An initial simple model is deformed by using region growing techniques to obtain a rough road approximation. This model will be refined by region competition. The result of this approach is that it delivers the simplest output vector information, fully recovering the road details as they are on the image, without performing any kind of symbolization. Therefore, we tried to refine a general road model by using a reliable method to detect transitions between regions. This method is proposed in order to obtain information for feeding large-scale Geographic Information System.     

高分辨率SAR 图像道路交叉口检测与识别新方法

道路交叉口是道路网的重要组成部分,对GIS 数据更新、影像匹配、目标检测等具有重要作用。由于受各种干扰以及道路与周围地物对比度不明显等影响,传统道路交叉口检测方法很难应用于高分辨率SAR 图像。该文提出一种直接检测识别道路交叉口的新方法。该方法先根据交叉口的灰度特征,利用形态学变换,全局搜索交叉口候选区域中心点位置|然后以此为局部窗口中心,采用多阈值Otsu分割出各个局部窗口内道路目标|接着根据交叉口的几何特征,通过矩形旋转得到角度均值图,获取与交叉口相连的道路个数,最终识别出交叉口的类型。使用1 m 机载高分辨率SAR 图像进行实验,结果证明该方法可有效提取出各种干扰下的交叉口目标。      

全尺寸目标激光脉冲后向散射回波功率测定和建模

运用粗糙面散射、激光脉冲散射理论,结合复杂目标粗糙表面相关建模参数,建立用于计算全尺寸复杂目标激光脉冲后向散射功率的理论模型.实验测量一种空中缩比目标模型后向散射激光脉冲回波功率,获取该缩比目标激光脉冲后向散射功率随接受天顶角的变化曲线.比较理论建模与实验测量数据,分析实验误差,证明了该理论模型的正确性.将建立的理论模型进一步应用于计算非合作空间全尺寸目标的激光脉冲回波功率.计算结果能够预估空间目标的激光散射特征,解决一些关于空间目标激光脉冲光学特征工程的应用问题.     

基于双层网格的海上电磁波传播模型研究

针对分段线性地形变换模型运算量较大的问题,该文提出基于双层网格的计算方法,实现了海上大尺度区域复杂电磁环境下电磁波传播特性快速精准的求解。在对宽角抛物方程模型和分段线性地形变换模型的分步傅里叶积分算法研究的基础上,将电磁场计算空间分为上下两层,通过降低计算高度和优化步长的方法,在保证计算精度的同时显著提高了运算效率。通过仿真,在光滑海面和粗糙海面两种条件下对双层网格模型的计算结果与原有模型进行比较,结果表明,所提方法计算误差较小,在粗糙海面条件下运算时间缩短到原模型的1/10。     

Plane wave pulse propagation through random media

The theory of plane wave pulse propagation through a random medium, under the forward-scattering assumption is presented. Since pulse propagation characteristics are determined by two-frequency mutual coherence functionGamma, a set of normalized curves is given forGammafor different propagation parameters (operating frequency, propagation distance, turbulence strength or density of scatterers, etc.). From the curves one can obtain the coherence bandwidth of a wave for a variety of situations. A received pulse form due to an input delta function is given in a normalized form which is applicable to the whole range of strong fluctuation. The results are applied to optical pulse propagation in dense clouds. It is shown that the high data rate optical pulse communication through clouds may be limited due to a narrow coherence bandwidth of the order of megahertz. A good agreement between the theoretical prediction and the available experimental data has been demonstrated for both the received pulse shapes and the pulse durations of an optical pulse in clouds.     

A Study of Nonlinearities and Intermodulation Characteristics of 3-Port Distributed Circulators

Results of a study of nonlinearities and intermodulation characteristics of 3-port distributed circulators are presented. Based on a rigorous theoretical analysis of the third-order nonlinearity in ferrites, analytical results are derived for the field strength and the power level of the intermodulation signal. These explicit results are applicable to high-power distributed circulators operating in VHF, UHF, and microwave frequencies. Measured intermodulation characteristics of an experimental distributed VHF high-power circulator are also presented.     

基于分形的粗糙海面三维抛物方程模型及其应用

风驱海浪随机起伏变化是海面环境的典型特征之一, 而较大的风浪通常会给海面无线通信带来重要的影响.传统的抛物方程(Parabolic Equationmethod, PE)模型在预测粗糙海面的电波传播时, 未能充分考虑海浪的电磁散射以及阴影效应等.针对以上不足, 文中基于三维抛物方程, 引入动力学分形方法, 对传统的抛物方程模型进行了改进研究.相比传统的Miller-Brown近似方法, 改进后的预测模型能更好地反映出海浪几何特征对电磁波传播的影响.最后以舰载雷达的有效探测范围为计算背景, 对粗糙海面的电波传播特性进行了仿真分析, 结果表明了该模型在区域级海面环境电波预测的可行性.