Inversion for atmosphere duct parameters using real radar sea clutter

This paper addresses the problem of estimating the lower atmospheric refractivity (M profile) under nonstandard propagation conditions frequently encountered in low altitude maritime radar applications. The vertical structure of the refractive environment is modeled using five parameters and the horizontal structure is modeled using five parameters. The refractivity model is implemented with and without a priori constraint on the duct strength as might be derived from soundings or numerical weather-prediction models. An electromagnetic propagation model maps the refractivity structure into a replica field. Replica fields are compared with the observed clutter using a squared-error objective function. A global search for the 10 environmental parameters is performed using genetic algorithms. The inversion algorithm is implemented on the basis of S-band radar sea-clutter data from Wallops Island, Virginia (SPANDAR). Reference data are from range-dependent refractivity profiles obtained with a helicopter. The inversion is assessed (ⅰ) by comparing the propagation predicted from the radar-inferred refractivity profiles with that from the helicopter profiles, (ⅱ) by comparing the refractivity parameters from the helicopter soundings with those estimated. This technique could provide near-real-time estimation of ducting effects.     

Monitoring of the ducting by a ground-based GPS receiver

In this paper, we describe the estimation of low-altitude refractivity structure from simulation and real ground-based GPS delays. The vertical structure of the refractive environment is modeled using three parameters, i.e., duct height, duct thickness, and duct slope. The refractivity model is implemented with a priori constraints on the duct height, thickness, and strength, which might be derived from soundings or numerical weather-prediction models. A ray propagation model maps the refractivity structure into a replica field. Replica fields are compared with the simulation observed data using a squared-error objective function. A global search for the three environmental parameters is performed using genetic algorithm. The inversion is assessed by comparing the refractivity profiles from the radiosondes to those estimated. This technique could provide near-real-time estimation of ducting effect. The results suggest that ground-based GPS provides significant atmospheric refractivity information, despite certain fundamental limitations of ground-based measurements. Radiosondes typically are launched just a few times daily. Consequently, estimates of temporally and spatially varying refractivity that assimilate GPS delays could substantially improve over-estimates using radiosonde data alone.     

Monitoring of ducting by using a ground-based GPS receiver

In this paper,we describe the estimation of low-altitude refractivity structure from simulation and real ground-based GPS delays.The vertical structure of the refractive environment is modeled using three parameters,i.e.,duct height,duct thickness,and duct slope.The refractivity model is implemented with a priori constraints on the duct height,thickness,and strength,which might be derived from soundings or numerical weather-prediction models.A ray propagation model maps the refractivity structure into a replica field.Replica fields are compared with the simulation observed data using a squarederror objective function.A global search for the three environmental parameters is performed using a genetic algorithm.The inversion is assessed by comparing the refractivity profiles from the radiosondes to those estimated.This technique could provide near-real-time estimation of the ducting effect.The results suggest that ground-based GPS provides significant atmospheric refractivity information,despite certain fundamental limitations of ground-based measurements.Radiosondes are typically launched just a few times daily.Consequently,estimates of temporally and spatially varying refractivity that assimilate GPS delays could substantially improve over-estimates caused by using radiosonde data alone.     

The estimation of lower refractivity uncertainty from radar sea clutter using the Bayesian-MCMC method

The estimation of lower atmospheric refractivity from radar sea clutter(RFC) is a complicated nonlinear optimization problem.This paper deals with the RFC problem in a Bayesian framework.It uses the unbiased Markov Chain Monte Carlo(MCMC) sampling technique,which can provide accurate posterior probability distributions of the estimated refractivity parameters by using an electromagnetic split-step fast Fourier transform terrain parabolic equation propagation model within a Bayesian inversion framework.In contrast to the global optimization algorithm,the Bayesian-MCMC can obtain not only the approximate solutions,but also the probability distributions of the solutions,that is,uncertainty analyses of solutions.The Bayesian-MCMC algorithm is implemented on the simulation radar sea-clutter data and the real radar seaclutter data.Reference data are assumed to be simulation data and refractivity profiles are obtained using a helicopter.The inversion algorithm is assessed(i) by comparing the estimated refractivity profiles from the assumed simulation and the helicopter sounding data;(ii) the one-dimensional(1D) and two-dimensional(2D) posterior probability distribution of solutions.     

Estimation of lower refractivity uncertainty from radar sea clutter using Bayesian-MCMC method

Estimation of lower atmospheric refractivity from radar sea clutter (RFC) is a complicated nonlinear optimization problem. This paper deals with the RFC problem in a Bayesian framework. It uses unbiased Markov Chain Monte Carlo (MCMC) sampling technique, which can provide accurate posterior probability distributions of the estimated refractivity parameters by using an electromagnetic split-step fast Fourier transform terrain parabolic equation propagation model within a Bayesian inversion framework. In contrast to the global optimization algorithm, the Bayesian-MCMC can obtain not only the approximate solutions, but also the probability distributions of the solutions, that is, uncertainty analyses of solutions. The Bayesian-MCMC algorithm is implemented on the simulation radar sea-clutter data and the real radar sea-clutter data. Reference data are assumed to be simulation data and refractivity profiles obtained with a helicopter. Inversion algorithm is assessed (i) by comparing the estimated refractivity profiles from the assumed simulation and the helicopter sounding data; (ii) the one-dimensional (1D) and two-dimensional (2D) posterior probability distribution of solutions.     

Remote sensing of atmospheric duct parameters using simulated annealing

Simulated annealing is one of the robust optimization schemes. Simulated annealing mimics the annealing process of the slow cooling of a heated metal to reach a stable minimum energy state. In this paper, we adopt simulated annealing to study the problem of the remote sensing of atmospheric duct parameters for two different geometries of propagation measurement. One is from a single emitter to an array of radio receivers (vertical measurements), and the other is from the radar clutter returns (horizontal measurements). Basic principles of simulated annealing and its applications to refractivity estimation are introduced. The performance of this method is validated using numerical experiments and field measurements collected at the East China Sea. The retrieved results demonstrate the feasibility of simulated annealing for near real-time atmospheric refractivity estimation. For comparison, the retrievals of the genetic algorithm are also presented. The comparisons indicate that the convergence speed of simulated annealing is faster than that of the genetic algorithm, while the anti-noise ability of the genetic algorithm is better than that of simulated annealing.     

遗传算法结合正则化方法反演海洋大气波导

针对正则化方法在解决实际反演问题时既能克服问题的不适定性又可以很大程度上抑制噪声和误差的传播, 本文提出了利用遗传算法结合正则化方法的新算法, 在遗传算法适应度函数中引入正则化项来反演波导参数; 然后对算法进行仿真试验, 结果表明新算法与传统遗传算法相比具有较高的反演精度, 并指出当噪声误差小于10%时, 算法具有较强的“去噪”性能; 最后利用机载雷达在Wallops岛探测的海表面处局部回波资料进行反演试验, 将反演结果与实测大气折射率廓线进行比较, 说明该算法的有效性. 新方法为海洋大气波导反演研究提供了一种新思路.     

红外大气折射率剖面分布模式

针对光电测量设备的大气折射误差实时修正以及红外激光传输研究等问题,利用2006年至2010年间在新疆戈壁地区获取的大气参数探空实验数据,计算得到了两个特定的波长,即1.32 m和4 m对应的大气折射率平均剖面分布,进而提出了一种实用的折射率剖面分布模式三参数指数分布模式。利用非线性最小二乘法,分别拟合得到了波长为1.32 m和4 m时的红外波在各季节内折射率的三参数指数剖面分布模式。采用统计得到的折射率剖面分布模式实时修正了光电设备的仰角测量数据,通过和实测模型的事后修正结果比较发现,二者的差值小于5,实现了对当地光学测量数据大气折射误差的实时、快速修正。     

Refractivity estimations from an angle-of-arrival spectrum

This paper addresses the probability of atmospheric refractivity estimation by using field measurements at an array of radio receivers in terms of angle-of-arrival spectrum.Angle-of-arrival spectrum information is simulated by the ray optics model and refractivity is expressed in the presence of an ideal tri-linear profile.The estimation of the refractivity is organized as an optimization problem and a genetic algorithm is used to search for the optimal solution from various trial refractivity profiles.Theoretical analysis demonstrates the feasibility of this method to retrieve the refractivity parameters.Simulation results indicate that this approach has a fair anti-noise ability and its accuracy performance is mainly dependent on the antenna aperture size and its positions.     

GPS/LEO掩星正则变换反演方法

利用无线电全息方法, 如正则变换方法或全谱反演方法, 可以有效地解决大气多路径条件下GPS掩星信号的反演问题. 本文采用正则变换方法反演掩星资料, 模拟仿真反演结果显示正则变换方法可以准确地反演包含大气多路径效应的信号. 在模拟信号的相位中加入不同程度的高斯相位噪声后, 正则变换方法的反演结果会受到不同程度的影响. 用正则变换方法对2007年第71天至73天共约4500个COSMIC数据进行处理. 将其折射率反演结果和atmPrf资料 (利用全谱反演方法计算得到) 一起, 与对应的ECMWF 分析场资料进行统计比较, 结果表明: 在5 km以下, 正则变换方法计算的折射率的相对误差的平均值普遍大于atmPrf资料. 其原因可能为: 正则变换方法将信号从LEO轨迹后传播至辅助屏, 造成孔径缩小, 精度下降. 同时也讨论了信号截断对低对流层中反演精度和掩星个数的影响. 关键词： 无线电掩星 大气多路径 多相位屏技术 正则变换方法     

大气波导条件下雷达海杂波功率仿真

考虑近海面大气折射率垂直梯度的变化, 采用曲面波频谱估计方法(CWSE)计算掠射角, 并结合修正的GIT海表反射率模型和雷达距离方程对大气波导条件下雷达海杂波功率进行仿真, 最后通过数值实验及与实测数据比较, 验证了CWSE方法的可行性. 关键词： 大气波导 雷达海杂波 曲面波频谱估计     

基于低密度奇偶校验码的MPPM比特符号映射及系统性能研究

建立了基于低密度奇偶校验(LDPC)码和多脉冲位置调制(MPPM)的无线光通信系统模型,给出了相应系统模型下的解码算法,研究了(m,2)MPPM的比特符号映射方式,提出了用改进的遗传算法(GA)搜索的优化映射方法,最后在大气湍流信道下进行了仿真。仿真结果表明基于LDPC码和MPPM的无线光通信系统性能明显优于未编码的MPPM系统,结合LDPC码和多光束发射技术可以提高系统抗强大气湍流影响的能力;通过GA优化的映射方法在不增加系统复杂性的情况下能进一步提高系统的纠错性能,可以获得更大的编码增益。     

基于湍流球泡折射的空间量子密钥分发性能分析

为了研究大气湍流对自由空间量子密钥分发的性能影响,将大气湍流建模为空间中随机分布的空气球泡,利用几何光学原理分析单光子在湍流球泡中的传播,定量计算了经过两次折射后由于偏振态变化造成的光子透射率比值k和误码率Ep的起伏,利用蒙特卡洛方法模拟了湍流折射率随机变化时二者的趋势;最后推导了经过湍流折射后的诱骗态空间量子密钥分发成码率公式并通过分析误码来源得到满足成码率需要的k值上限,建立偏振误码率与入射角和湍流折射率的关系并得到Ep的安全阈值.仿真结果表明当入射角在44.8°~76.5°,湍流折射率在1~1.33范围内可以满足误码率的上限约束.该研究为湍流条件下进行空间量子通信实验提供了理论参考.     

高功率微波在电离层中传播的折射率研究

 高功率微波在电离层中的传播特性主要由其折射率的变化决定，而高功率微波的大气折射率与相应传输层面的电子浓度有关。结合电离层电子浓度分布模型对电子浓度和大气折射率进行了数值模拟，对电离层折射率以及折射率垂直梯度相对于高度的变化特性进行了分析。结合射线描迹法对高功率微波波束传播高度、仰角和距离进行了修正，并在低功率微波下进行实验验证，证实修正值更接近实际值。     

无线电掩星滑动频谱方法和后传播方法的分析比较

本文详细介绍了滑动频谱方法,并通过模拟仿真和实测资料处理与后传播方法进行比较. 通过对模拟仿真信号反演发现:后传播方法和滑动频谱方法均能削弱大气多路径的影响,后传播方法在一定程度上优于滑动频谱方法;在模拟信号的相位中加入高斯噪声对后传播方法影响不大,但对滑动频谱方法影响较大,尤其在边界层以下. 分别用后传播方法和滑动频谱方法对2007年第71天至73天共约4500个COSMIC掩星数据进行处理. 将折射率反演结果与ECMWF分析场资料进行统计比较,结果显示:滑动频谱方法反演的掩星廓线深度大于后传播方法;后 关键词： GPS/LEO掩星 多相位屏模型 后传播方法 滑动频谱方法     

Modified genetic algorithm-based sub-pixel mapping

Sub-pixel mapping (SPM) is a promising way to predict the location of endmembers within mixed pixels at the sub pixel level. SPSAM is a real time processing algorithm for SPM, but it will generate a lot of isolated sub pixels because land cover classes were assigned to sub pixels in order. In this letter, a novel method is proposed to realize SPM. It contains two main steps: sub-pixel/pixel spatial attraction model (SPSAM) is first used to generate the initial SPM result; and then modified genetic algorithm (MGA) is applied as the post-processing method to obtain more accurate results. Three different sets of data are used for experiments: simple artificial images and two sets of real remote sensing images. The results show MGA/SPSAM outperforms the conventional SPM methods.     

垂直天线阵观测信息反演大气折射率廓线

利用垂直天线阵观测得到的电磁场信息建立目标泛函,从电磁波抛物方程传播模式出发,利用偏微分方程最优控制中的伴随方法研究大气折射率廓线反演问题. 针对反演的不适定性,采用正则化思想对目标泛函进行改造,并根据变分同化思想构建反演迭代格式. 数值模拟试验验证了理论算法的可行性. 由于采用分步Fourier算法求解电磁波抛物方程传播模式和伴随模式过程中产生的固有误差随着传播距离的增加累积增大,反演廓线在传播距离较远时不能收敛于观测廓线. 在这种情况下,引入较好的初猜廓线和背景场可以有效地改进反演结果. 关键词： 大气折射率 电磁波抛物方程 变分伴随 正则化     

A new phase-screen method for electromagnetic wave propagation in turbulent flows using large-eddy simulation

Use of large-eddy simulation (LES) data in electromagnetic wave propagation modeling is not very common because of the high computational cost involved. A new phase-screen method is proposed to model radio wave propagation, in the atmospheric turbulence, using the resolved scale refractivity obtained from LES. The proposed method offers the same level of accuracy, as the one already existing in the literature, at much cheaper cost.     

Optimal design of loudspeaker arrays for robust cross-talk cancellation using the Taguchi method and the genetic algorithm

An optimal design technique of loudspeaker arrays for cross-talk cancellation with application in three-dimensional audio is presented. An array focusing scheme is presented on the basis of the inverse propagation that relates the transducers to a set of chosen control points. Tikhonov regularization is employed in designing the inverse cancellation filters. An extensive analysis is conducted to explore the cancellation performance and robustness issues. To best compromise the performance and robustness of the cross-talk cancellation system, optimal configurations are obtained with the aid of the Taguchi method and the genetic algorithm (GA). The proposed systems are further justified by physical as well as subjective experiments. The results reveal that large number of loudspeakers, closely spaced configuration, and optimal control point design all contribute to the robustness of cross-talk cancellation systems (CCS) against head misalignment.     

一种新的大气折射率剖面模型构建方法

针对现有大气折射率剖面模型中干项简化模型较多、使用中难以取舍和湿项简化模型精度较低等问题,利用某台站实测探空数据,对现有几种大气折射率剖面模型的精度进行了分析。在此基础上,基于小波聚类和EOF(经验正交函数)分析方法,构建了一个能够考虑天气特征的大气折射率剖面改进模型,并利用实测数据对其精度进行了验证。结果表明:改进模型拟合精度较现有模型精度有明显改进。其中,干项模型能够充分考虑台站本地气候特征,精度更高;湿项模型将天气类型细分为四类,比现有模型精度最大提高了约6个折射率单位。同时,改进模型天气类型划分方法较容易被非气象专业人员理解,便于此模型推广应用。