To reconstruct the missing data of the total electron content(TEC) observations, a new method is proposed, which is based on the empirical orthogonal functions(EOF) decomposition and the value of eigenvalue itself. It is a self-adaptive EOF decomposition without any prior information needed, and the error of reconstructed data can be estimated. The interval quartering algorithm and cross-validation algorithm are used to compute the optimal number of EOFs for reconstruction.The interval quartering algorithm can reduce the computation time. The application of the data interpolating empirical orthogonal functions(DINEOF) method to the real data have demonstrated that the method can reconstruct the TEC map with high accuracy, which can be employed on the real-time system in the future work.
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.
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 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.
电离层对无线电通信、卫星导航有重要的影响,因此对电离层电子总含量(total electron content,TEC)的预报研究十分重要,而目前国际上的各种经验电离层预报模型的精度只有60%左右,不能满足实际需求.本文提出一种新的TEC预报模型:利用经验正交函数对TEC数据进行时空分解,利用遗传算法结合混沌预测的思想对时间场系数进行非线性时间序列预测,从而达到对TEC数据预报的目的.实验结果表明,此方法可较好地对TEC数据进行不同时间尺度的预测,提前1,2,4,7 d的预报精度分别达到0.32,0.48,0.68,0.94 TECU.
使用2006年12月—2008年11月COSMIC(constellation observing system for meteorology,ionosphere and climate)掩星湿廓线资料对第二对流层顶的全球分布特征进行统计,对比三个站点的无线电探空仪和COSMIC的对流层顶资料,研究结果表明:1)第二对流层顶的出现频率在副热带急流区较高,冬季在北半球为50%—70%,在南半球为20%—40%;2)赤道带的第二对流层顶出现频率约为20%—26%,与越赤道急流和对流层顶上的毛卷云有关;3)在副热带急流区,第一对流层顶的温度基本高于第二对流层顶;4)在热带,对流层顶厚度和第二对流层顶出现频率随纬度减小;热带以外,对流层顶厚度随纬度增加,在冬半球60有最大值7—8km;5)单站点对流层顶的日变化剧烈程度与COSMIC和探空仪的对流层顶高度偏差正相关.
