时幅转换技术及其在激光测距系统中的应用

简要介绍了时幅转换技术[1 ] 的原理、实现方法以及在激光测距系统中的应用。给出了实际时幅转换特性的试验数据及精度分析。利用时幅转换器测量时间的精度和分辨率可以分别达到几十皮秒和几皮秒的量级。将这一技术应用于传统的激光测距系统后 ,可以将测距精度和分辨率由原来的分米级分别提高到厘米级和毫米级。     

空间目标共视观测定位的误差分析

通过两台光电望远镜对空间目标共视观测能够定位空间目标,并且能够解决光电望远镜短弧测角数据的初轨确定问题,但其定位精度与空间目标和两台光电望远镜所形成的观测几何有关。首先对空间目标共视观测定位误差进行分析,然后推导其均方根误差的解析表达式,最后基于长春站和上海佘山站并结合不同轨道高度的低轨激光星CPF(Consolidated Prediction Format)星历生成仿真共视观测数据,用来对空间目标共视观测定位以及定轨精度进行分析。结果表明,两台光电望远镜对低轨空间目标的定位精度能够达到100 m,利用定位数据进行初轨确定可以得到轨道的半长轴误差小于10 km。     

LEO空间目标的非协同共视观测及初轨确定

测角数据的初轨确定(IOD)是通过光学观测技术进行空间目标编目的 关键,然而对于低地球轨道(LEO)空间目标,地基光学观测所获得的数据弧长较短且不包含距离信息.因此,在进行IOD时,所得轨道的误差往往较大,难以应用于进一步的工作中.针对上述问题,研究了LEO空间目标的非协同共视观测技术及其初轨确定,并基于统计学提出了一种利用非协同共视观测技术定位空间目标的新方法.结合中国科学院空间目标与碎片观测网的光学测角数据进行了实验验证,结果表明,所提方法对Ajisai卫星定位的均方根(RMS)误差小于100 m,对空间碎片CZ-2C R/B定位的RMS误差小于200 m,优于传统的三角视差法.随后,将上述定位结果用于IOD,所得轨道半长轴的误差在1 km左右.     

基于探针光调制的皮秒分辨X-ray探测方法与实验

高能密度物理研究中涉及许多单次皮秒现象的诊断测量, 然而对单次X-ray脉冲形状、X-ray与激光脉冲的皮秒精度同步依然是极具挑战的课题. 传统行波选通分幅相机受电子渡越时间限制, 难以突破40 ps时间分辨极限. 本文围绕半导体中光学探针光的全光调制效应, 提出一种以低温GaAs材料为基础, 实现皮秒时间分辨X-ray探测的新方法, 详细阐述了该探测器的工作机理、器件参数设计和时间分辨能力. 通过飞秒激光打靶实验, 验证了其概念设计的正确性. 结果表明该探测器具有约1.5 ps时间响应和10 ps时间分辨能力, 通过材料优化可将时间分辨提升 至1 ps以内.     

超高速分幅相机曝光时间测量的误差分析

基于超高速光电分幅相机曝光的控制原理,从光纤切割精度和激光器精确同步两个主要影响因素出发,讨论了采用超快激光脉冲和光纤阵列形成光延时结合CCD相机的方法测量高速相机曝光时间的误差,并提出了降低误差的技术措施。分析表明,光纤切割精度和激光器精确同步引入的误差仅为皮秒级,对纳秒级的相机曝光时间测量的影响可以忽略。采用光纤束阵列法,实验测量了超高速光电分幅相机的曝光时间,对比测量值与标称值,二者吻合良好,验证了此方法的有效性。     

基于正弦波磁光调制的方位失调角精确测量方法

针对传统基于正弦波磁光调制的方位失调角测量系统存在测量精度不高的问题,提出了一种新的系统方位失调角测量模型以提高系统测量精度。通过分析传统的基于正弦波磁光调制的方位失调角测量原理发现,由于采用省略高阶项的贝塞尔函数展开式表示磁光调制后的信号,引入了信号截断误差和方法误差,影响了系统测量精度。在分析基础上推导建立了一种基于纯三角函数表示的无理论误差的方位失调角测量新模型并进行了仿真。仿真结果表明,利用推导建立的失调角测量新模型,系统测量精度明显高于传统方法,这对重新理解基于正弦波磁光调制的方位失调角测量系统原理、提高系统测量精度具有一定的参考意义。     

北斗实时卫星共视时间传递技术及其性能评估

全球导航卫星系统（Global Navigation Satellite System,GNSS）时间传递技术以其低成本、高精度、广覆盖范围等特点，广泛应用到高精度时频领域。传统卫星共视技术利用全球卫星导航时间比对标准（Common GNSS Generic Time Transfer Standard,CGGTTS）共视文件实现事后高精度时间传递，很难实现实时时间传递。为满足数字换流站、电力物联网、移动通信等对实时、高精度时间传递的需求，研究了基于北斗三号全球卫星导航定位系统（BDS-3）伪距观测数据的实时卫星共视技术，开展了短基线和西安-三亚长基线北斗实时卫星共视时间传递实验来评估实时共视时间传递性能。实验结果表明北斗实时卫星共视时间传递精度优于1 ns，可为时频系统、数字换流站等应用领域提供纳秒级时间同步和纳秒级时间溯源服务。     

基于傅里叶光学原理的新型凹面光栅衍射效率测量方法

凹面衍射光栅兼具色散分光与光束聚焦功能,同时具有像差校正、低杂散光、无鬼线和高信噪比等优势而受到光谱仪器领域的广泛关注。衍射效率作为凹面光栅最重要的技术指标之一,其测量技术水平逐渐成为光谱仪器行业最为关注的课题之一。传统方法一般采用双单色仪结构实现凹面光栅衍射效率的测量,该方法主要存在两方面问题,一是测量标准反射镜和待测光栅的出射光谱带宽不同,二是光栅叠级、杂散光的影响;上述问题的存在降低了高性能凹面光栅衍射效率测量的准确性。本文提出了一种基于傅里叶光学原理测量凹面光栅衍射效率的新方法;针对该方法建立了凹面光栅衍射效率测量的数学模型,并采用光学追迹和傅里叶光学方法相结合对其进行了仿真分析,从而验证了该方法的正确性;针对动镜横移误差、倾斜误差、光源稳定性、动镜运动距离误差等因素影响凹面光栅衍射效率测量精度的问题,提出引入辅助探测器的方法来进一步提高衍射效率测量精度,并对有无辅助探测器情况下的上述误差对衍射效率的影响进行了数学推导和仿真分析,分析结果表明引入辅助探测器可以有效抑制了上述误差对凹面光栅衍射效率测量的影响。对比传统双单色仪测量方法而言,该方法不仅能够解决传统测量方法存在的问题,同时还具有多波长同时测量、高光通量、高分辨率、高波数精度等优势,可以有效提高凹面光栅衍射效率的测量精度和测量效率。     

两轴光电跟踪仪高仰角跟踪盲区分析

 从轴准直误差、动态滞后误差两方面分析了采用俯仰轴叠加于方位轴光机座结构方式的光电跟踪仪在高俯仰角跟踪时的误差变化及由此导致的盲区问题,从轴准直误差和动态滞后误差两方面对高仰角跟踪盲区的形成及其空间分布进行分析,并用MATLAB进行了仿真,给出跟踪盲区随方位、俯仰角变化的的分布图形。从盲区分布图形可以看出：光电跟踪仪在性能一定的情况下,跟踪盲区随着仰角增大而增大,并结合直线航路给出这两种误差导致的跟踪盲区的计算方法。跟踪直线航路实验数据显示跟踪误差随着仰角增大而增大。     

基于光栅色散干涉条纹的菲佐光干涉望远镜共相检测方法研究

菲佐光干涉望远镜实现高分辨率成像的关键是各子孔径之间相位平移误差的共相检测. 基于物理光学基本原理, 论证了两个子孔径在单色光条件下其远场干涉条纹峰值偏移量与其相位平移误差之间的近似线性关系, 提出了一个波长范围内的平移误差检测方法; 进而提出了基于光栅色散干涉条纹的共相检测方法, 并对其可行性、检测精度和检测范围进行了理论分析与仿真实验. 结果表明, 该方法在原理上可以实现对两孔径的相位平移误差进行直接检测, 50 μm范围内平移误差的检测精度优于20 nm, 解决了既有方法可能存在的2π模糊性及无法判断平移误差正负的问题. 该方法为共相检测技术的进一步研究提供了新的途径和参考.     

The method and experiment analysis of two-way common-view satellite time transfer for compass system

Time synchronization between ground and satellites is a key technology for satellite navigation system. With dual-channel satellite, a method called Two-Way Common-View(TWCV) satellite time transfer for Compass system is proposed, which combines both characteristics of satellite common-view and two-way satellite-ground time transfer. By satellite-ground two-way pseudo-range differencing and two stations common-view differencing, this TWCV method can completely eliminate the influence of common errors, such as satellite clock offset, ephemeris errors, troposphere delay and station coordinates errors. At the same time, ionosphere delay related to signal frequency is also weakened significantly. So the precision of time transfer is improved much more greatly than before. In this paper, the basic principle is introduced in detail, the effect of major errors is analyzed and the practical calculation model in the Earth-fixed coordinate system for this new method is provided. Finally, experiment analysis is conducted with actual Compass observing data. The results show that the deviation and the stability of the satellite dual channel can be better than 0.1 ns, and the accuracy of the two-way common-view satellite time transfer can achieve 0.4 ns. All these results have verified the correctness of this TWCV method and model. In addition, we compare this TWCV satellite time transfer with the independent C-band TWSTFT(Two-Way Satellite Time and Frequency Transfer). It shows that the result of the TWCV satellite time transfer is in accordance with the C-band TWSTFT result, which further suggests that the TWCV method is a remote high precision time transfer technique. The research results in this paper are very important references for the development and application of Compass satellite navigation system.     

Applications of two-way satellite time and frequency transfer in the BeiDou navigation satellite system

A two-way satellite time and frequency transfer(TWSTFT) device equipped in the BeiDou navigation satellite system(BDS)can calculate clock error between satellite and ground master clock. TWSTFT is a real-time method with high accuracy because most system errors such as orbital error, station position error, and tropospheric and ionospheric delay error can be eliminated by calculating the two-way pseudorange difference. Another method, the multi-satellite precision orbit determination(MPOD)method, can be applied to estimate satellite clock errors. By comparison with MPOD clock estimations, this paper discusses the applications of the BDS TWSTFT clock observations in satellite clock measurement, satellite clock prediction, navigation system time monitor, and satellite clock performance assessment in orbit. The results show that with TWSTFT clock observations, the accuracy of satellite clock prediction is higher than MPOD. Five continuous weeks of comparisons with three international GNSS Service(IGS) analysis centers(ACs) show that the reference time difference between BeiDou time(BDT) and golbal positoning system(GPS) time(GPST) realized IGS ACs is in the tens of nanoseconds. Applying the TWSTFT clock error observations may obtain more accurate satellite clock performance evaluation in the 104 s interval because the accuracy of the MPOD clock estimation is not sufficiently high. By comparing the BDS and GPS satellite clock performance, we found that the BDS clock stability at the 103 s interval is approximately 10.12, which is similar to the GPS IIR.     

Orbit determination for geostationary satellites with the combination of transfer ranging and pseudorange data

Geostationary satellites(GEOs) play a significant role in the regional satellite navigation system.Simulation experiments show that the clock corrections could be mitigated through a single strategy or double differencing strategies for a navigation constellation,but for the mode of individual GEO orbit determination,high precision orbit and clock correction could not be obtained in the orbit determination based on the pseudorange data.A new GEO combined precise orbit determination(POD) strategy is studied in this paper,which combines pseudorange data and C-band transfer ranging data.This strategy overcomes the deficiency of C-band transfer ranging caused by limited stations and tracking time available.With the combination of transfer ranging and pseudorange data,clock corrections between the GEO and the stations can be estimated simultaneously along with orbital parameters,maintaining self-consistency between the satellite ephemeris and clock correction parameters.The error covariance analysis is conducted to illuminate the contributions from the transfer ranging data and the psudoranging data.Using data collected for a Chinese GEO satellite with 3 C-band transfer ranging stations and 4 L-band pseudorange tracking stations,POD experiments indicate that a meter-level accuracy is achievable.The root-mean-square(RMS) of the post-fit C-band ranging data is about 0.203 m,and the RMS of the post-fit pseudorange is 0.408 m.Radial component errors of the POD experiments are independently evaluated with the satellite laser ranging(SLR) data from a station in Beijing,with the residual RMS of 0.076 m.The SLR evaluation also suggests that for 2-h orbital predication,the predicted radial error is about 0.404 m,and the clock correction error is about 1.38 ns.Even for the combination of one C-band transfer ranging station and 4 pseudorange stations,POD is able to achieve a reasonable accuracy with the radial error of 0.280 m and the 2-h predicted radial error of 0.888 m.Clock synchronization between the GEO and tracking stations is achieved with an estimated accuracy of about 1.55 ns,meeting the navigation service requirements.     

COMPASS time synchronization and dissemination—Toward centimetre positioning accuracy

In this paper we investigate methods to achieve highly accurate time synchronization among the satellites of the COMPASS global navigation satellite system (GNSS). Owing to the special design of COMPASS which implements several geo-stationary satellites (GEO), time synchronization can be highly accurate via microwave links between ground stations to the GEO satellites. Serving as space-borne relay stations, the GEO satellites can further disseminate time and frequency signals to other satellites such as the inclined geo-synchronous (IGSO) and mid-earth orbit (MEO) satellites within the system. It is shown that, because of the accuracy in clock synchronization, the theoretical accuracy of COMPASS positioning and navigation will surpass that of the GPS. In addition, the COMPASS system can function with its entire positioning, navigation, and time-dissemination services even without the ground link, thus making it much more robust and secure. We further show that time dissemination using the COMPASS-GEO satellites to earth-fixed stations can achieve very high accuracy, to reach 100 ps in time dissemination and 3 cm in positioning accuracy, respectively. In this paper, we also analyze two feasible synchronization plans. All special and general relativistic effects related to COMPASS clocks frequency and time shifts are given. We conclude that COMPASS can reach centimeter-level positioning accuracy and discuss potential applications.     

Satellite-station time synchronization information based real-time orbit error monitoring and correction of navigation satellite in Beidou System

Satellite-station two-way time comparison is a typical design in Beidou System(BDS)which is significantly different from other satellite navigation systems.As a type of two-way time comparison method,BDS time synchronization is hardly influenced by satellite orbit error,atmosphere delay,tracking station coordinate error and measurement model error.Meanwhile,single-way time comparison can be realized through the method of Multi-satellite Precision Orbit Determination(MPOD)with pseudo-range and carrier phase of monitor receiver.It is proved in the constellation of 3GEO/2IGSO that the radial orbit error can be reflected in the difference between two-way time comparison and single-way time comparison,and that may lead to a substitute for orbit evaluation by SLR.In this article,the relation between orbit error and difference of two-way and single-way time comparison is illustrated based on the whole constellation of BDS.Considering the all-weather and real-time operation mode of two-way time comparison,the orbit error could be quantifiably monitored in a real-time mode through comparing two-way and single-way time synchronization.In addition,the orbit error can be predicted and corrected in a short time based on its periodic characteristic.It is described in the experiments of GEO and IGSO that the prediction accuracy of space signal can be obviously improved when the prediction orbit error is sent to the users through navigation message,and then the UERE including terminal error can be reduced from 0.1 m to 0.4 m while the average accuracy can be improved more than 27%.Though it is still hard to make accuracy improvement for Precision Orbit Determination(POD)and orbit prediction because of the confined tracking net and the difficulties in dynamic model optimization,in this paper,a practical method for orbit accuracy improvement is proposed based on two-way time comparison which can result in the reflection of orbit error.     

The principle of the positioning system based on communication satellites

It is a long dream to realize the communication and navigation functionality in a satellite system in the world. This paper introduces how to establish the system, a positioning system based on communication satellites called Chinese Area Positioning System (CAPS). Instead of the typical navigation satellites, the communication satellites are configured firstly to transfer navigation signals from ground stations, and can be used to obtain service of the positioning, velocity and time, and to achieve the function of navigation and positioning. Some key technique issues should be first solved; they include the accuracy position determination and orbit prediction of the communication satellites, the measuring and calculation of transfer time of the signals, the carrier frequency drift in communication satellite signal transfer, how to improve the geometrical configuration of the constellation in the system, and the integration of navigation & communication. Several innovative methods are developed to make the new system have full functions of navigation and communication. Based on the development of crucial techniques and methods, the CAPS demonstration system has been designed and developed. Four communication satellites in the geosynchronous orbit (GEO) located at 87.5°E, 110.5°E, 134°E, 142°E and barometric altimetry are used in the CAPS system. The GEO satellites located at 134°E and 142°E are decommissioned GEO (DGEO) satellites. C-band is used as the navigation band. Dual frequency at C1=4143.15 MHz and C2=3826.02 MHz as well as dual codes with standard code (CA code and precision code (P code)) are adopted. The ground segment consists of five ground stations; the master station is in Lintong, Xi’an. The ground stations take a lot of responsibilities, including monitor and management of the operation of all system components, determination of the satellite position and prediction of the satellite orbit, accomplishment of the virtual atomic clock measurement, transmission and receiving navigation signals to and from each satellite. In the north, the south, the east, the west and the center of Chinese main land, the function of CAPS demonstration system is checked and measured. In cars and on board the system is also checked and measured. The results are as follow: CA-code, horizontal positioning accuracy, 15–25 m (1 σ), vertical, 1–3 m; P-code, horizontal positioning accuracy, 8–10 m (1 σ), vertical, 1–3 m; velocity accuracy, CA-code, 0.13–0.30 m/s, P-code, 0.15–0.17 m/s; time accuracy, CA-code, 160 ns, P-code, 13 ns; determination accuracy of orbit ≤2 m. About 20 million US $ and two years are spent for the development of demonstration. A complete CAPS system is now being established. Supported by the National Natural Science Foundation of China (Grant No. 10453001), the National Basic Research Program of China (Grant No. 2007CB815500), the National High Technology Research and Development Program of China (Grant No. 2004AA105030), and the Funds of the Chinese Academy of Sciences for Key Topics in Innovation Engineering (Grant No. KGCXI-21)     

An analysis of the wide area differential method of geostationary orbit satellites

This work aims to obtain a wide area differential method for geostationary orbit (GEO) constellation. A comparison between the dilution of precision (DOP) of four-dimensional (4D) calculation including satellite clock errors and ephemeris errors and that of three-dimensional (3D) calculation only including ephemeris errors with the inverse positioning theory of GPS shows the conclusion that all the 3D PDOPs are greatly reduced. Based on this, a basic idea of correcting satellite clock errors and ephemeris errors apart is put forward, and moreover, a specific method of separation is proposed. Satellite clock errors are separated in a master station with time synchronization, and all the remaining pseudo-range errors after the satellite clock errors have been deducted are used to work out ephemeris corrections of all GEO satellites. By a comparative analysis of user positioning accuracy before and after differential, the wide area differential method is verified to be quite valid for GEO constellation. Supported by the National Natural Science Foundation of China (Grant No. 10778715), the National Key Basic Research Development Program of China (Grant No. 2007CB815502), and the Scientific Research Fund of Hunan Provincial Education Department (Grant No. 08B039)     

A new method for determination of satellite orbits by transfer

The original idea of a new method for determination of satellite orbits by transfer is from Two-Way Satellite Time and Frequency Transfer (TWSTFT). The original method is called “determination of satellite orbit by transfer”. The method is not only for determination of satellite orbit but also for the time transfer with high accuracy and precision. The advantage is that the accuracy and the precision for determination of satellite orbit are very high and the new method is favorable for various applications. The combination of various signals disseminated and received forms various modes of satellite orbit determinations. If receivers at stations receive the own station-disseminated signals via a satellite transponder, it forms an orbit determination mode called “receiving the own station-disseminated signals mode”. If receivers at all stations receive the signals disseminated from the master station via satellite transponders, it forms an orbit determination mode called “receiving the master station-disseminated signals mode”. If all of receivers at stations receive all stations-disseminated signals via satellite transponders, it forms an orbit determination mode called “receiving all stations-disseminated signals mode”. Also there are other combinations of signals for satellite orbit determination. For different orbit determination modes with different signal combinations, their rigorous formulae of processing are hereby presented in this paper. The accurate and the precise satellite orbit determination for both of the modes, “receiving the own station-disseminated signals mode” and “receiving the master station-disseminated signals mode” is attempted. It shows that the accuracy and precision for both of modes are nearly the same, the ranging accuracy is better than 1 cm, and the observation residuals of satellite orbit determination are better than 9 cm in the observation duration of 1 day. Supported by the National Basic Research and Development Program of China (Grant No. 2007CB815503100453001)     

Orbit determination and time synchronization for a GEO/IGSO satellite navigation constellation with regional tracking network

Aiming at regional services,the space segment of COMPASS (Phase I) satellite navigation system is a constellation of Geostationary Earth Orbit (GEO),Inclined Geostationary Earth Orbit (IGSO) and Medium Earth Orbit (MEO) satellites.Precise orbit determination (POD) for the satellites is limited by the geographic distribution of regional tracking stations.Independent time synchronization (TS) system is developed to supplement the regional tracking network,and satellite clock errors and orbit data may be obtai...