Analysis of cross-beam resolution effects in rainfall rate profileretrieval from a spaceborne radar

The performance (stability and accuracy) of a range profiling algorithm (kZS), using the measurement of surface echo as a constraint on total path integrated attenuation, for rainfall retrieval from a spaceborne radar was presented and discussed by C. Matzler (1987). Omitting other causes of errors previously examined, the present authors focus specifically on possible bias due to nonuniform beam filling effects. This problem is studied analytically to identify the physical origin of the biasing terms. In addition, bias in rainfall profile estimates is quantified through simulations of Ku-band spaceborne radar data processing, featuring the intercept of a raincell model by the downward looking radar beam     

A novel multicast routing algorithm in sparse splitting WDM network with power attenuation constraint

With the increasing requirement for communication bandwidth, all-optical network has been more and more important owning to its large traffic capability. Multicasting is an important technology in wavelength division multiplexing (WDM) optical network, and has been studied in many works. In this paper, we consider the multicasting technology on all-optical metropolitan area network (MAN) with maximum power attenuation constraint. The objective is to minimize total cost of a multicasting request. This problem is NP-hard. We propose a heuristic, named Power-Constraint Fix-Destination-Path (PC-FDP) algorithm, to solve this maximal power-loss constrained minimizing cost multicasting problem. It means that, during the process of building a multicasting tree, when a destination is reached and its power satisfies the constraint, the path from source to it would be fixed in the tree. Simulation results show that, all multicasting trees building the proposed algorithm satisfy the power constraint, with slight increasing of the total cost.     

雨衰减预测中的降雨率调整因子概念

利用ITUR数据库地面视距链路和地空链路雨衰减数据,分析了传统雨衰减预报中所使用的基于柱状雨胞模型的雨衰减物理模型导出的路径调整因子与实测数据之间的矛盾.在此基础上,基于指数雨胞建立的雨衰减物理模型,通过理论分析导出了降雨率调整因子的概念.利用降雨率调整因子,可以解释实测数据的主要特征,表明：基于指数雨胞的雨衰减物理模型是合理的,利用降雨率调整因子的概念,可为发展新的地面视距链路和地空链路雨衰减预报模式和方法提供理论依据.     

基于低秩稀疏约束的穿墙雷达成像算法

针对穿墙雷达(TWR)成像过程中墙杂波与成像空间分别具有低秩性和稀疏性的特点,提出了一种基于低秩稀疏约束的穿墙雷达成像算法.所提成像算法通过奇异值软阈值法和l1范数最小化技术进行迭代求解低秩稀疏约束优化问题,实现在墙体强反射波存在的探测环境中基于压缩感知框架对墙后隐蔽目标的准确成像重建.仿真和实验数据的处理结果验证了所提成像算法的有效性和准确性.     

求解约束满足问题的改进蚁群优化算法

为了克服传统的回溯算法在求解大型的约束满足问题时效率低,难以在合理的时间内求解这一问题。提出了基于启发式搜索的不完备性算法。结合不同算法特性,主要在蚁群优化元启发式约束求解算法的基础上提出了改进：一是在搜索之前用弧相容检查进行预处理以压缩搜索空间,二是提出了一种新的蚁群算法参数设置方案,提高算法的适应性。最后将改进后的算法应用于求解随机问题和组合优化问题。实验结果表明,改进后的算法求解效率得到大幅度提高。     

一种基于改进Hough变换的雷达检测方法

Hough变换是一种用于雷达长时间积累的有效方法,提出一种改进的Hough变换方法.与传统的方法不同,新方法把数据空间中的点映射到由斜率和截距定义的参数空间中,并通过对同一时刻到来的所有数据进行整体平移,实现对数据的映射.该方法降低了Hough变换的计算量.理论分析和仿真试验验证了新方法的有效性.     

Spatial correlation coefficients of rainfall intensity inferred from statistics of rainfall intensity and rain attenuation

On the basis of the reliable statistics of rainfall rate and rainfall attenuation for 8 localities in Europe, the spatial correlation coefficient of point rainfall intensity was inferred for each locality from the cumulative distributions of attenuation and rainfall intensity by inversely applying the modified Morita and Higuti rainfall attenuation prediction method. It was found that for European regions the spatial correlation coefficient with an exponential dependence on the horizontal distance is more appropriate for the prediction of rainfall attenuation than that proposed by Morita and Higuti for the Japanese climate. It was also found that although the spatial correlation characteristic varies significantly from one locality to another its variance is not so significant within a particular ccir rainfall climatic zone. This suggests that in predicting the rainfall attenuation it is desirable to employ the spatial correlation coefficient appropriate for the locality to be estimated.     

抽样子空间约束改进大数据谱聚类算法

在分析经典谱聚目标函数与加权核k-means目标函数等价基础上,设计了一种基于抽样子空间约束的改进大规模数据谱聚类算法,算法通过加权核k-means迭代优化避免矩阵特征分解的大量资源被占用,通过数据抽样及聚类中心的子空间约束,避免全部核矩阵都被使用,从而降低经典算法的时间空间复杂度。理论分析和实验结果表明,改进算法保持与经典算法相近聚类精度,提高了聚类效率,验证了改进算法的有效性。     

基于截距分析的改进雷达信号分选算法

常用的雷达分选算法易出现脉冲重复间隔谐波和同部雷达信号脉冲序列断裂的问题,鉴于此提出了一种基于脉冲到达时间拟合直线截距分析的改进雷达信号分选算法。该算法通过对到达时间拟合直线截距的分析,判断出上述2种情况,整合相应脉冲序列,从而得到正确的分选结果。到达时间截距分析算法能增强雷达信号分选算法的鲁棒性,降低算法对搜索容限的依赖,具有良好的工程应用价值。仿真表明,改进的信号分选算法比序列差值直方图算法的分选概率高20%。     

基于空间变换迭代的SIFT特征图像匹配算法

SIFT（Scale Invariant Feature Transform）特征由于具有旋转、平移和尺度不变性在图像匹配中得到了广泛的应用。但直接运用SIFT特征进行匹配,存在两个问题:易受匹配参数的影响,出现较多的错漏匹配现象;只适用于相似变换情况下的图像匹配,对于高维的仿射变换情况则难以奏效,而在实际图像匹配中这种情况更为常见。针对以上问题,提出了一种空间变换迭代的SIFT特征图像匹配方法。把SIFT特征点集匹配转化为SIFT特征向量与点集的几何分布信息相关的函数最优化求解问题,通过在确定性退火框架下,迭代求解空间仿射变换与点集匹配对应关系,最终得到最优的SIFT特征点匹配关系。仿真实验表明:在较大仿射变换情况下该方法仍能实现图像SIFT特征点集的正确匹配。     

On the rain attenuation dynamics: spatial‐temporal analysis of rainfall rate and fade duration statistics

Knowledge about the dynamic characteristics of rain attenuation is of utmost importance for many applications in terrestrial and satellite communication systems operating at frequencies above 10 GHz. Long‐term rain rate statistics and rain rate duration statistics are usually available from meteorological data. In this paper, a spatial–temporal analysis is employed in order to evaluate the rain attenuation power spectrum of a terrestrial/satellite path. The predicted power spectrum is compared with experimental data. Based on the spectral analysis of rainfall rate a method for converting rain rate duration statistics to link fade duration statistics is also proposed. Fade duration statistics are presented for terrestrial and satellite links and compared with available experimental data. The agreement between the predicted results and the experimental data has been found to be quite encouraging. Finally, numerical results are presented for various climatic zones, elevation angles and frequencies. Some very useful conclusions concerning the dynamic properties of rain attenuation for a microwave path are deduced. Copyright © 2003 John Wiley & Sons, Ltd.     

利用遗传算法求取雷达目标极点分布

散射物体自然频率(极点)是目标识别可以利用的一个基本特征,传统的理论求解极点的方法一般是用迭代法求取由矩量法得到的矩阵方程系数行列式的零点.矩阵方程系数矩阵的病态性是其最大的缺点.文章提出了用遗传算法获得极点的方法,对遗传算法应用于求取雷达目标极点方面的问题做了理论和算法分析.由于球体目标的极点可以解析获得,所以利用了球体作为实验验证的例子.并计算了有限长圆柱的结果.实验结果表明算法相对于传统的围线积分法不仅避免了病态矩阵的问题,而且简单易行,结果可靠.     

Frequency and polarisation scaling of microwave attenuation during rainfall

Measurements are presented from eastern Canada of the polarisation-dependent ratio of microwave attenuation due to rainfall for vertical and horizontal linear polarisations, and of the frequency-dependent ratio of attenuation for a given polarisation. The exponent of the usual power law of frequency scaling of attenuation is 1.93±0.15 (SD) in the 11?17 GHz frequency range.     

Measurements of rainfall attenuation at 8 and 15 GHz

Measurements of attenuation at frequencies of 8 and 15 GHz, and their correlation with rainfall rate, along a 15.78 km path near Ottawa, are described. Empirical expressions which relate the observed attenuation to the measured rainfall rate are derived and compared with similar expressions obtained on the basis of earlier theoretical studies of the problem. It is concluded that while the theoretical predictions of attenuation in rain are reasonably satisfactory, at least for rains observed at Ottawa, there is a definite tendency for observed attenuations at low rainfall rates to be somewhat higher than the expected values. The cumulative distribution of rainfall attenuation over a six-month period is compared with the attenuation predicted on the basis of average rainfall data obtained during the last five years. Although the agreement between observation and prediction, using the theoretical relation between rainfall rate and attenuation, is good for path attenuations greater than 2 dB, it can be greatly improved if the empirical expression relating rainfall rate to attenuation is used.     

激光损伤测试系统衰减片参数的改进遗传算法优化

光学元件激光损伤测试系统中的轮盘式衰减器衰减片参数的选取直接影响测试精度。本文采用遗传算法,采用实数编码的参数编码方式,适应度值排序和随机选取结合选择算子,杂交算子中选择随机交叉两个必然产生交叉的个体的部分基因,变异算子根据交叉概率的大小对个体进行位操作,经此改进的算法对激光损伤测试系统中的机械式激光能量衰减器的3组15片衰减片进行了参数优化。优化结果表明:15片衰减片中选取8种不同衰减率,经优化后输出的能量衰减率间隔小于测试激光能量的3 %,线性度误差为12.4 %。     

Dual-parameter radar rainfall measurement from space: a test resultfrom an aircraft experiment

An aircraft experiment has been conducted with a dual-frequency ( X/Ka-bands) radar to test various rainfall retrieval methods from space. The authors test a method to derive raindrop size distribution (DSD) parameters from the combination of a radar reflectivity profile and a path-integrated attenuation derived from the surface return, which may be available from most spaceborne radars. The test results indicate the feasibility of the dual-parameter radar measurement from space in achieving a better accuracy in quantitative rainfall remote measurements     

结合look-ahead值排序的自适应分支求解算法

基于新近提出的自适应分支约束求解框架,结合look-ahead值启发式,提出一种新的约束求解算法AdaptBranchLVO。为验证算法效率,在标准测试库上进行了充分对比实验。结果表明,新提出算法在效率上明显优于已有的自适应分支求解算法。     

New radar studies of slant-path attenuation due to rain

Approximately 40 h of data from the summer of 1976 were employed in a comparison of radar and radiometer estimates of slant-path attenuation due to rain. McGill Radar Weather Observatory is situated 20 km west of Montreal; the radiometers, separated by 18 km at two sites located about 90 km northwest of the radar, had fixed antennas pointed approximately southeast at an elevation of 18.5 deg. Values of radar reflectivity along the two radiometer paths were used to calculate the slant-path attenuation at 13 GHz as a function of time with a 1 min resolution for direct comparison with the radiometer measurements. It was found that the cumulative distribution of attenuation inferred by radar from each site could be made to agree satisfactorily with the radiometer distribution assuming that rain was present everywhere along the path with a Marshall-Palmer distribution and applying a 1 dB correction to the independently-determined radar calibration. This agreement, close to within a fraction of a decibel, gives confidence to the use of radar records in compiling attenuation statistics. An example is presented of a new application of such records, namely the assessment of rain-induced interference over adjacent earth-space paths.     

Inference of raindrop size distribution from attenuation and rain rate measurements

A method to infer the raindrop size distribution from the measurements of point rain rate and rain attenuation at a frequency in centimeter or millimeter wave bands is proposed. This method is applied to the results of field propagation experiments at 81.8, 34.5, and 11.5 GHz through natural rain. It is shown that, if an appropriate frequency is employed, this method is effective as a frequency-scaling method for short terrestrial propagation paths.