排序方式: 共有12条查询结果,搜索用时 31 毫秒
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This paper puts forward a new method to solve the electromagnetic parabolic equation (EMPE) by taking the vertically-layered inhomogeneous characteristics of the atmospheric refractive index into account. First, the Fourier transform and the convo- lution theorem are employed, and the second-order partial differential equation, i.e., the EMPE, in the height space is transformed into first-order constant coefficient differential equations in the frequency space. Then, by use of the lower triangular characteristics of the coefficient matrix, the numerical solutions are designed. Through constructing ana- lytical solutions to the EMPE, the feasibility of the new method is validated. Finally, the numerical solutions to the new method are compared with those of the commonly used split-step Fourier algorithm. 相似文献
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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. 相似文献
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This paper addresses the problem of estimating lower
atmospheric refractivity under the nonstandard propagation conditions
frequently encountered in low altitude maritime radar applications.
The vertical structure of the refractive environment is modeled by
using a five-parameter model, and the horizontal structure is modeled
as range-independent. The electromagnetic propagation in the
troposphere is simulated by using a split-step fast Fourier
transform based on parabolic approximation to the wave equation. A
global search marked as a modified genetic algorithm (MGA) for the 5
environmental parameters is performed by using a genetic algorithm
(GA) integrated with a simulated annealing technique. The retrieved
results from simulated runs demonstrate the ability of this method
to make atmospheric refractivity estimations. A comparison with the classical GA
and the Bayesian Markov Chain Monte Carlo (Bayesian-MCMC) technique
shows that the MGA can not only shorten the inverse time but also
improve the inverse precision. For real data cases, the inversion
values do not match the reference data very well. The
inverted profile, however, can be used to synoptically describe
the real refractive structure. 相似文献
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Ray tracing/correlation approach to estimation of surface-based duct parameters from radar clutter 下载免费PDF全文
This paper describes a technique to estimate surface-based
duct parameters by using a simple ray tracing/correlation method.
The approach is novel in that it incorporates the Spearman rank-order
correlation scheme between the observed surface clutter and the
surface ray density for a given propagation path. The simulation
results and the real data results both demonstrate the ability of
this method to estimate surface-based duct parameters. Compared with
the results obtained by a modified genetic algorithm combined with the
parabolic wave equation, the results retrieved from the ray
tracing/correlation scheme show a minor reduction in accuracy but a
great improvement on computation time. Therefore the ray
tracing/correlation method might be used as a precursor to more
sophisticated and slower techniques, such as genetic algorithm and
particle filters, by narrowing the parameter search space and
providing a comprehensive and more efficient estimation algorithm. 相似文献
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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 相似文献
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高效液相色谱法定量测定采油微生物发酵菌液中的有机酸 总被引:1,自引:0,他引:1
采用反相高效液相色谱法(RP-HPLC)在Kromasil C18分析柱上,以0.015 mol/L磷酸二氢钠缓冲液(pH=2.3)和乙腈(体积比为96∶4)的二元流动相分离测定了采油微生物发酵液中的有机酸,流动相的流速为1.0mL/min,采用紫外检测器在210 nm处对有机酸进行测定.结果表明有机酸浓度在0.05~1.5 g/L时其峰面积与相应的质量浓度有良好的线性关系,其r大小等于0.9990,测定结果的RSD都小于4.0%(n=8),平均回收率均为100±4%以内.该方法具有测定结果准确可靠,操作简便快速,重现性好等特点. 相似文献