射电天文自适应抗干扰算法研究

全球性卫星导航系统占用了L波段在1.1 GHz~1.6 GHz之间约150 M带宽,严重限制了射电天文在该频段的观测。将通信、雷达等领域的自适应滤波方法应用于消除"北斗二号"卫星信号给中性氢(HI)21 cm谱线观测带来的射频干扰(Radio Frequency Interference,RFI)。为了提高最小均方误差(Least Mean Square,LMS)自适应算法的性能,在对一类传统变步长最小均方误差算法研究的基础上,提出了步长与误差信号之间的一种新的函数关系,进一步改善了自适应滤波算法的性能。在相同收敛速度或者相同稳态误差的前提下,改进后的算法具有更小的稳态误差或者更快的收敛速度。计算机仿真实验结果与理论分析一致,验证了改进后的变步长自适应滤波算法在射电天文射频干扰消除中的性能优于传统算法。     

基于自适应滤波的干扰消除方法研究

射电天文信号非常微弱,电磁环境对射电望远镜观测至关重要,通常可以利用地形、建立无线电宁静区、进行电磁屏蔽与防护等手段来减小电磁干扰.然而,仍有一些干扰难以屏蔽.故提出了一种基于自适应滤波的干扰消除方法,可用于复杂噪声环境中天文信号的提取.该方法借助自适应横向滤波器,采用最小均方(Least Mean Square, LMS)误差算法,以系统误差和收敛性为评判标准,通过改变步长与阶数对滤波效果进行优化,仿真结果显示该滤波器能在保证算法收敛的前提下有效提取信号.为了检验该算法的有效性,选取了新疆天文台南山26 m射电望远镜和Parkes 64 m射电望远镜记录的观测数据,采用设计的滤波器分别对不同的实测数据进行测试,验证了该滤波器的有效性.理论分析与实验结果一致表明该方法能有效消除天文观测中的干扰信号,具有一定的实用性.     

近距离罗兰-C信号周期识别的数字化方法初探

对判断罗兰-C脉冲峰值的算法作了改进。对加有噪声的近距离罗兰- C脉冲仿真信号的采样值用改进的算法进行计算后,可识别信号周期并给出相位编码信息。对改进后的算法的有效性用MATLAB进行了验证,并用MODELSIM对改进的算法进行了仿真实现。结果表明：在一定的信噪比条件下,改进后的算法初步实现了对近距离罗兰-C信号周期识别的数字化,具有一定的实用性。     

BPL时号定时校准原理和方法

为保证BPL长波授时时号(以国家授时中心(NTSC)保持的UTC(NTSC)为基准)的准确度,必须对该时号进行定时校准(确定发射时号与发播工作钟同步时定时校准信号的相位)。阐述了定时校准的原理和方法。与传统罗兰-C系统校准方法不同,该方法选择发射天线电流取样信号基准过零点而非定时控制单元基本定时信号为定时校准点,消除了因锁相控制精度不足引起的误差,提高了时号精度。该方法可以作为罗兰-C授时系统的通用校准方法。     

我国西部罗兰台站定位性能分析

罗兰导航系统(Long range navigation)是全球卫星导航系统的有效备份和补充.罗兰信号以地波形式沿地球表面传播,随着传播距离的增加,地波信号受到地面电参数的影响会出现一定程度的传播延时,信号的场强也会逐渐减弱.为分析我国西部罗兰台站的定位性能,从理论角度分析了不同介质类型中二次时延随距离的变化关系,并结合电磁波传播规律计算了场强随距离的变化.根据罗兰接收机最低性能标准,分析了西部台站的覆盖区域以及定位范围,计算了定位区域内的几何精度因子,结果显示定位范围内大部分区域的几何精度因子小于6.在计算区域内仿真西部台站定位误差,分析结果表明:就定位而言,西部台站几何布局较为合理,但是由于二次时延的影响,纬度和经度方向定位误差较大,必须采用差分等抑制观测误差的方法提高定位精度.为扩大西部罗兰台站的定位覆盖区域,接收机的接收能力有待提升.     

一种基于MUSIC算法的天地波识别方法

基于我国BPL长波脉冲信号的特征,利用MUSIC(多信号分类)算法对BPL天、地波延迟进行估计,实现天、地波识别。对传统谱估计IFFT(快速傅里叶逆变换)算法和现代谱估计MUSIC算法进行了仿真和比较,结果表明,这两种方法在较低信噪比条件下可有效分离天、地波,且识别误差都能控制在±5μs内,但MUSIC算法比IFFT算法具有更高的精度和分辨率。     

LAMOST一维光谱提取算法的分析与比较

针对LAMOST (Large Sky Area Multi-Object Fiber Spectroscopic Telescope)2维光谱图像数据,对6种抽谱算法进行了分析与比较.比较的算法包括孔径法、轮廓拟合法、直接反卷积方法、基于Tikhonov正则化的反卷积抽谱算法、基于自适应Landweber迭代的反卷积抽谱算法以及基于Richardson-Lucy迭代的反卷积抽谱算法.通过实验对这些算法在信噪比和分辨率两个方面进行了比较,发现基于Tikhonov正则化的反卷积抽谱算法、基于自适应Landweber迭代的反卷积抽谱算法以及基于RichardsonLucy迭代的反卷积抽谱算法是6种算法中最为可靠的3种抽谱算法.最后,对今后的工作进行了展望.     

比值校正法在射电频谱中的应用

分子谱线可以在射电频谱上显现,但是采用离散数字功率谱分析算法会引入离散误差,难以获得分子谱线准确的频谱信息。针对射电频谱上离散数字功率谱分析带来的频率偏移问题进行比值校正法研究,该方法是频谱校正方法的一种,特点在于算法简单,方便快捷。利用射频信号相同、分辨率不同和射频信号不同、分辨率不同情况下,归一化频率偏移量的变化确定该方法的校正效果,最终实现了射频为80.0 MHz,141.8 MHz和270.8 MHz的频谱校正,将相应的频谱分辨率提高到7.5 Hz/channel。通过实验结果对比,确定了测试系统的最佳频率分辨率为50 Hz/Channel或200 Hz/channel。     

罗兰-C数据链在BPL授时中的应用研究

用户在利用中国BPL长波授时技术时,首先需要粗同步,然后才可以得到精确时间信息。介绍当前常用的罗兰-C数据链调制方式．提出了一种BPL时码信号调制方法及编码格式,从而使BPL具有自主授时功能,更好地为用户服务．     

对弱信号CCD图像噪声的最佳化处理

本文在分析CCD读出图像噪声的统计特性和目前CCD图像预处理的基础上,提出了对CCD读出数据的最佳化处理方法。该方法对CCD读出噪声和其它随机噪声都有较好的抑制效果,使用该方法可以从迭加有随机噪声的数据中得到信号的最佳估值,提高弱信号CCD读出图像的信噪比。     

一种基于RTAI实时操作系统的相关跟踪处理机

引入倾斜校正自适应光学技术到月球激光测距中,详细介绍了倾斜校正自适应光学的相关跟踪原理,给出了一种基于实时操作系统RTAI的相关跟踪波前处理机的设计结果.该波前处理机采用绝对差分算法,使用通用CPU,基于Linux硬实时扩展系统BTAI实现对波前的实时处理.实验结果证明,它的相关跟踪处理帧频为1 KHz,并且具有集成度...     

A modified land surface temperature split window retrieval algorithm and its applications over China

Due to the difficulties in correcting the influences of the atmosphere absorbability and the Earth surface emissivity diversification, the retrieval of LST (land surface temperature) from satellite data is a challenging task. In this paper, a modified Becker's split window LST inversion algorithm is developed for retrieving LST from the NOAA-16/17 AVHRR data. A new set of parameters for Becker's LST algorithm is proposed. The algorithm is developed from a surface brightness temperature dataset generated from the MODTRAN program, which uses a range of surface parameters and atmospheric quantities as inputs. The 10-day composites of the channels 4 and 5 brightness temperature data of NOAA-17 AVHRR (1-km resolution) are used to generate the clear-sky LST. As a validation of the algorithm, the retrieved LST is compared with MODIS LST of same period and area. The two LST products are found to be consistent, with the absolute difference being about 2.5 K for most areas. The NOAA retrieved LST is also compared with in-situ ground surface 0-cm measurements taken from 257 meteorological stations, which cover overall China area for the three periods of satellite observations. The comparison shows that the correlation between the retrieved LST and in-situ measurements is over 0.90 and the RMSE (root mean square error) is about 3.4 K.     

An algorithm for a near real-time data processing of GPS common-view observations

Near real-time transfer of GPS common-view data is no longer a problem, but near real-time data processing of the data still calls for study, because it is not yet achieved by the usual smoothing and filtering techniques. Based on the characteristics of the GPS common-view data, a Kalman filtering algorithm is designed for estimating the time difference between two sites, while greatly reducing the observational noise. The algorithm is applied to the time difference between the National Time Service Center (NTSC) of China and the Communications Research Laboratory (CRL) of Japan (Over 2000 km apart), and to that between the CRL and the Korean Research Institute of Standards and Sciences (KRIS) (over 1000 km apart). The root mean square errors of the results obtained by the Kalman filter relative to those obtained from the Circular T of BIPM are less than 2.9 ns and 2.6 ns, in the two cases. Further, it is pointed out that, when multi-site data within a common-view network are available we can further improve the accuracy of the time comparisons by indirect observation adjustment. This statement was justified by application to the data from all three stations, i.e. NTSC, CRL, and KRIS.     

GPS近实时共视观测资料处理算法研究

GPS共视资料的高精度快速处理可实现近实时共视时间传递，常见的平滑方法不能满足近实时共视的要求。分析GPS共视资料特点，设计一种卡尔曼滤波算法，对共视资料进行近实时处理，以便削弱观测噪声，估计异地钟差，对相距2000多公里的中国科学院国家授时中心(NTSC)与日本通信综合研究所(CRL)，和相距1000多公里的CRL与韩国计量科学研究院(KRIS)的共视观测资料处理结果表明：卡尔曼滤波算法所得钟差与根据BIPMT公报所得钟差的均方根误差分别优于2．9ns和2．6ns，为进一步提高比对精度，最后对近实时共视应用于多站点间相互比对的情况，提出在卡尔曼滤波算法基础上使用间接观测平差处理技术，根据共视网络中站点间距离设置观测权值，通过解矛盾方程组得到两站钟差，以NTSC、CRL和KRIS3站比对为例，以BIPMT公报得到的钟差为标准，对间接观测平差处理前后的数据比较表明，近实时比对精度可进一步提高。     

Adaptive particle swarm optimization for optimal orbital elements of binary stars

The paper presents an adaptive particle swarm optimization (APSO) as an alternative method to determine the optimal orbital elements of the star η Bootis of MK type G0 IV. The proposed algorithm transforms the problem of finding periodic orbits into the problem of detecting global minimizers as a function, to get a best fit of Keplerian and Phase curves. The experimental results demonstrate that the proposed approach of APSO generally more accurate than the standard particle swarm optimization (PSO) and other published optimization algorithms, in terms of solution accuracy, convergence speed and algorithm reliability.     

重力梯度场球谐谱分析的研究

卫星重力梯度测量任务将获取全球范围内高精度重力场信息。为利用重力梯度测量数据来提高重力场模型的精度,本文从球谐函数谱分析理论出发,导出了重力梯度场球谐谱分析的迭代算法公式。数值模拟结果表明：该迭代算法的收敛性极好,且高阶次位系数的收敛趋势较低阶次的收敛趋势要好得多。     

Formation of spectral lines in a dynamically active stochastic and multicomponent atmosphere

This paper is devoted to a determination of the statistical mean quantities describing spectral line radiation of dynamically active stochastic and multicomponent atmospheres. The lines in LTE are considered so that the effects of multiple scattering can be neglected. Two types of problem are discussed. In the first it is assumed that the realization of one or another type of nonthermal motion depends on the type of structural element and in the other this type of dependence is absent, i.e., it is supposed that the assumed random values of the velocity are distributed according to a law that is common to all the components. Particular attention is paid to a determination of the relative mean square deviation of the intensity of the observed radiation. It appears that the distinctive feature of the relative mean square deviation of the radiation in a line formed in a dynamically active stochastic atmosphere is local “spikes” (maxima) in the wings of the line. The theoretical results in this paper are compared with spectral observations of quiescent solar prominences obtained in framework of the SOHO space mission. __________ Translated from Astrofizika, Vol. 50, No. 1, pp. 121–134 (February 2007).     

An Orbital Prediction Algorithm for LEO Satellites Based on Optical Observations of Short Arcs at Single Station

The forecasting technique of the target tracking based on the short arcs at single station is an important way to guarantee that high-precision photoelectric theodolites can normally track and capture the targets in unconventional environments. We construct the tracking prediction algorithm based on nonlinear filter, which can provide the guiding data for the closed loop tracking under normal circumstances. At the same time we also construct the target prediction algorithm based on the nonlinear transformation, without valid observational data, which can provide a track guidance for the theodolite and ensure that the targets will not be lost. It is demonstrated that the nonlinear filtering is more effective than the EKF (extended Kalman filter) in the tracking prediction algorithm of the short arcs at single station. The results indicate that the nonlinear filter designed in this paper can be used as the guiding algorithm for the optical tracking equipments. And its guiding accuracy is in the same order of magnitude of the theodolite's random measurement accuracy. When the systematic error of the equipments reaches 50″, the accuracy can achieve 20″ for predictions in 60 s. This still satisfies the requirement of the field of view of the tracking equipments.     

基于混沌时间序列的Volterra自适应滤波极移预报方法

针对极移复杂的时变特性, 根据混沌相空间坐标延迟重构理论, 提出一种基于Volterra自适应滤波的极移预报方法. 首先, 利用最小二乘拟合算法分离极移序列中的线性趋势项、钱德勒项和周年项, 获得线性极移、钱德勒极移和周年极移的外推值; 其次, 通过C-C关联积分法对最小二乘拟合残差序列进行相空间重构, 并利用小数据量法计算残差序列的最大Lyapunov指数验证其混沌特性, 在此基础上, 构建Volterra自适应滤波器对残差序列进行预测; 最后, 将线性极移、钱德勒极移和周年极移的外推值以及最小二乘拟合残差的预测值相加获得极移最终预报值. 利用国际地球自转服务局(International Earth Rotation and Reference Systems Service, IERS)提供的极移数据进行1--60d跨度预报, 并将预报结果分别与国际地球定向参数预报比较竞赛(Earth Orientation Parameters Prediction Comparison Campaign, EOP PCC)结果和IERS A公报发布的极移预报产品进行对比, 结果表明: 对于1--30d的短期预报, 该方法的预报精度与EOP PCC最优预报方法相当, 当预报跨度超过30d时, 该方法的预报精度低于EOP PCC最优预报方法, 优于参与EOP PCC的其他方法; 与IERS A公报相比, 该方法的短期预报效果较好, 当预报跨度增加时预报精度低于IERS A公报. 预报结果表明该方法更适合于极移短期预报.