共查询到20条相似文献，搜索用时 62 毫秒
1.
《天文和天体物理学研究(英文版)》2012,(6):601-624
This paper reviews positioning systems in the context of communication systems.First,the basic positioning technique is described for location based service(LBS) in mobile communication systems.Then the high integrity global positioning system(iGPS) is introduced in terms of aspects of what it is and how the low Earth orbit(LEO) Iridium telecommunication satellites enhance the global positioning system(GPS).Emphasis is on the Chinese Area Positioning System(CAPS) which is mainly based on commercial geostationary(GEO) communication satellites,including decommissioned GEO and inclined geosynchronous communication satellites.Characterized by its low cost,high flexibility,wide-area coverage and ample frequency resources,a distinctive feature of CAPS is that its navigation messages are generated on the ground,then uploaded to and forwarded by the communication satellites.Fundamental principles and key technologies applied in the construction of CAPS are presented in detail from the CAPS validation phase to its experimental system setup.A prospective view of CAPS has concluded it to be a seamless,high accuracy,large capacity navigation and communication system which can be achieved by expanding it world wide and enhancing it with LEO satellites and mobile base stations.Hence,this system is a potential candidate for the next generation of radio navigation after GPS. 相似文献
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Orbit Determination Using Satellite—to—Satellite Tracking Data 总被引：3，自引：0，他引：3
Ying－ChunLiu LinLiu 《中国天文和天体物理学报》2001,1(3):281-286
1 INTRODUCTIONThe tracking arc-length should be increased in order to approve the accuracy in orbitdetermination of LEO (Low Earth Orbit) satellites. The local ground-based tracking networkdoes not provide sufficient orbit coverage for the user satellites. The most promising methodis to use high orbiting satellites, such as GPS and TDRS, as trackers to observe the usersatellites. For examPle, tWO geosynclironous satellites could cover more than 85% of the orbitof any given user sate… 相似文献
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Yu Lu Jian-Yan WeiNational Astronomical Observatories Chinese Academy of Sciences Beijing luyu 《中国天文和天体物理学报》2003,3(5):395-409
We use controlled N-body simulation to investigate the dynamical processes (dynamical friction, tidal truncation, etc.) involved in the merging of small satellites into bigger halos. We confirm the validity of some analytic formulae proposed earlier based on simple arguments. For rigid satellites represented by softened point masses, the merging time scale depends on both the orbital shape and concentration of the satellite. The dependence on orbital ellipticity is roughly a power law, as suggested by Lacey & Cole, and the dependence on satellite concentration is similar to that proposed by White. When merging satellites are represented by non-rigid objects, Tidal effects must be considered. We found that material beyond the tidal radius are stripped off. The decrease in the satellite mass might mean an increase in the merging time scale, but in fact, the merging time is decreased, because the stripped-off material carries away a proportionately larger amount of of orbital energy and angular momentum. 相似文献
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Ying Yang Lan-Qiang Zhang Nan-Fei Yan Jin-Sheng Yang Zhen Li Teng-Fei Song Xue-Jun Rao andChang-Hui Rao 《天文和天体物理学研究(英文版)》2024,(3):226-238
The 2.5 m wide-field and high-resolution solar telescope(WeHoST) is currently under developing for solar observations. WeHoST aims to achieve high-resolution observations over a super-wide field of view(FOV) of5′ × 5′, and a desired resolution of 0.3″. To meet the scientific requirements of WeHoST, the ground-layer adaptive optics(GLAO) with a specially designed wave front sensing system is as the primary consideration. We introduce the GLAO configuration, particularly the wave front sensing sch... 相似文献
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《天文和天体物理学研究(英文版)》2016,(5)
The light reflected from planets is polarized mainly due to Rayleigh scattering, but starlight is normally unpolarized. Thus it provides an approach to enhance the imaging contrast by inducing the imaging polarimetry technique. In this paper, we propose a high-contrast imaging polarimeter that is optimized for the direct imaging of exoplanets, combined with our recently developed stepped-transmission filter based coronagraph. Here we present the design and calibration method of the polarimetry system and the associated test of its high-contrast performance. In this polarimetry system, two liquid crystal variable retarders(LCVRs) act as a polarization modulator, which can extract the polarized signal. We show that our polarimeter can achieve a measurement accuracy of about 0.2% at a visible wavelength(632.8 nm)with linearly polarized light. Finally, the whole system demonstrates that a contrast of 10~(-9) at 5λ/D is achievable, which can be used for direct imaging of Jupiter-like planets with a space telescope. 相似文献
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We present the first detailed photometric analysis of ATO J108.6991+27.8306(hereinafter as J108). The shortperiod close binary J108 was observed by the Nanshan 1 m Wide Field Telescope of the Xinjiang Astronomical Observatory. The obtained BVRI-band light curves were used to determine the photometric solution by using the 2003 version of the Wilson-Devinney code. J108 is a typical deep( f > 50%), low mass ratio(q < 0.25)overcontact binary system with a mass ratio of q = 0.1501 and a fill-o... 相似文献
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Yu Wang Hai-Yan Zhang Hao Hu Shi-Jie Huang Wei-Wei Zhu Guo-Ping Zhi Tao Zhang Zhan-Chun Fan Li Yang 《天文和天体物理学研究(英文版)》2021,(1)
As the most sensitive single-dish radio telescope,the Five-hundred Aperture Spherical radio Telescope(FAST)is very susceptive to radio frequency interference(RFI)from active radio services.Moreover,due to the rapid development of space applications and research,satellite interference has become one of the main RFI sources for FAST,particularly at the L band.Therefore,we have developed several measures to mitigate satellite RFI.On the one hand,an antenna with 4.5-meter diameter has been constructed and installed at the FAST site to detect the satellite interference in the frequency band between 1 to 5 GHz.Meanwhile,we have developed a satellite RFI database based on the FAST sky coverage,the observing frequency bands,and known satellite systems.By combining the satellite RFI monitoring antenna and the database,we have established a satellite RFI mitigation system.With this system,we can not only track satellites to collect their characteristics and update the database but also help the observer to program the observing plan by predicting satellite interference.During the practical observation of FAST at the L band,the feasibility of this system to mitigate satellite RFI has been proved.In particular,the system effectively avoids strong satellite interference from entering the main beam of the telescope and causing receiver saturation. 相似文献
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Under some circumstances in using the Global Navigation Satellite System （GNSS）, since navigation signals from the satellites are blocked a receiver cannot simultaneously track four or more satellites to estimate its 3-dimensional （3D） coordinates and clock bias. This paper proposes a Doppler Shift-and-Range （DS-R） positioning algorithm with which pseudoranges and Doppler shifts are simultaneously measured. The measurement results are used as inputs to four equations in the algorithm, and the 3D position can be estimated from the equations. Through this approach the algorithm can achieve real-time 3D positioning. By synthesizing multi-frequency observational results and adopting a new method of jointly using code-carrier phases, this algorithm expectably has accuracies similar to those of the standard approach of point positioning. 相似文献
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《天文和天体物理学研究(英文版)》2021,(7)
The National Solar Observatory is currently developing the Accurate Infrared Magnetic Field Measurements of the Sun(AIMS). The primary mirror of the AIMS solar telescope is an off-axis parabolic with a diameter of 1 m and with a large off-axis amount of 1 m. Due to the surface figure of the primary mirror under the used state is directly related to image quality of the whole system, a computer-generated hologram(CGH) is carried out to test the primary mirror, and the test results are used to polish the mirror to a higher surface accuracy. However, the fact that the distortion exists in the testing results leads to the failure of a further guide to deterministic optical processing. In this paper, a distortion correction method is proposed, which uses an orthogonal set of vector polynomials to mapping the coordinates of the mirror and the pixels of fringes, and then an interpolation method is adopted to obtain the corrected results. The testing accuracy by using CGH is also verified by an auto-collimate test experiment. According to the distorted corrected results, the root-mean-square of the surface figure is about 1/50λ(λ=632.8 nm) after polishing. 相似文献
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《天文和天体物理学研究(英文版)》2020,(4)
This paper is devoted to the primary spectro-polarimetric observation performed at the New Vacuum Solar Telescope(NVST) of China since 2017, and our aim is to precisely evaluate the real polarimetric accuracy and sensitivity of this polarimetry by using full Stokes spectro-polarimetric observations of the photospheric line Fe I 532.4 nm. In the work, we briefly describe the salient characteristic of the NVST as a polarimeter in terms of technology and then characterize its instrumental polarization based on the operation in 2017 and 2019. It is verified that the calibration method utilizing the instrumental polarization calibration unit(ICU) is stable and credible. The calibration accuracy can reach up to 3 × 10~(-3).Based on the scientific observation of NOAA Active Region 12645 on 2017 April 5, we estimate that the residual cross-talk from Stokes I to Stokes Q, U and V, after the instrumental polarization calibration,is about 4 × 10~(-3) on average, which is consistent with the calibration accuracy and close to the photon noise. The polarimetric sensitivity(i.e., the detection limit) for polarized light is of the order of 10~(-3) with an integration time over 20 s. Slow modulation rate is indeed an issue for the present system. The present NVST polarimeter is expected to be integrated with a high-order adaptive optics system and a field scanner to realize 2 D vector magnetic field measurements in the following instrumentation update. 相似文献
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为了研究低轨通信卫星多普勒定位性能,首先分析了低轨卫星的对地覆盖特性、信号传输特性以及多普勒频移特性,推导了多普勒定位原理和方法,提出了适用于多普勒定位的精度因子.基于已在轨的铱星和全球星系统,解算了全球范围可见卫星数和定位精度因子,并对相应测站进行了定位仿真实验和误差分析.结果表明:对于铱星和全球星系统,随着纬度降低,卫星可见数减小,多普勒几何精度因子变大;多普勒定位结果精度同时受到频率测量精度、卫星位置误差以及卫星速度误差影响,当卫星位置误差小于10 m、卫星速度误差小于0.1 km·s-1时,对定位结果影响不大,此时频率测量精度成为影响定位精度的决定性因素,且当频率测量精度为0.01 Hz时,定位精度可达1.18 m. 相似文献
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中国区域定位系统（Chinese Area Positioning System,CAPS）是基于通信卫星的转发式卫星导航系统,基本原理是导航信号由地面导航站上行,经通信卫星转发向地面广播,用户接收机接收导航信号和电文实现导航定位。在试验验证阶段,CAPS仅采用同步轨道通信卫星进行信号的转发和广播,用户接收机利用气压测高技术实现高程辅助下的定位解算。为了描述CAPS水平定位误差的分布,作者定义了高程辅助算法下的东精度衰减因子（Dilution of PrecisionEast,EDOP）和北精度衰减因子（Dilution of Precision North,NDOP）。根据CAPS星座分布,分析系统覆盖范围内高程辅助下EDOP和NDOP数值,结果表明CAPS的EDOP和NDOP是关于赤道南北对称,关于同步轨道通信卫星的平均经度子午圈对称。在平均经度子午圈附近,EDOP出现最小值;在同一纬度圈上,离平均子午圈越远,EDOP数值越大。在CAPS覆盖区域内,任一格点上的NDOP总是大于EDOP,当用户由低纬度地区向高纬度地区移动时,在站心坐标系内卫星在南北方向拉开的距离增大,NDOP变小。利用北京、上海、长春、西安、乌鲁木齐和昆明6个CAPS测站进行仿真分析,结果表明本文提出的EDOP和NDOP可用于估算星座空间布局对用户伪距测量误差的放大程度,并可以解释CAPS接收机在高程辅助下水平定位精度东西方向总是优于南北方向的现象。进一步的实测数据分析表明,EDOP和NDOP可以用来估算南北方向和东西方向的定位精度。 相似文献
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北斗卫星导航系统(BeiDou navigation satellite System, BDS)已于2020年7月正式建成并开通, 北斗三号(BDS-3)在旧信号B1I和B3I的基础上, 增加了B1C、B2a新信号. 为了全面评估BDS-3的新信号B1C、B2a的定位性能, 试验了GPS (Global Positioning System)、BDS-3、BDS-2/BDS-3新旧信号的定位性能和BDS系统不同频点与GPS组合定位性能, 对BDS (B1I+B3I、B1C/B2a)+GPS (L1+L2)组合静态PPP (Precise Point Positioning)定位性能进行分析, 并与单卫星系统对比分析. 试验结果表明: BDS-3 (B1C/B2a)在East (E)、\lk North (N)、Up (U)方向的定位精度优于1.25cm、0.89cm、1.67cm, BDS-3新旧频点在E、N方向上定位精度与GPS L1/L2在同一水平上, U方向上新频点定位精度高于GPS L1/L2和BDS-3旧频点, 较旧频点定位精度提升了34.2%, 新频点收敛时间25.9min比旧频点提升了12.7%; 相较于BDS、GPS单系统, 组合系统BDS/GPS定位精度和收敛时间有了明显的提高, BDS-3 (B1C/B2a)+GPS在E、N方向上与BDS-3 (B1I/B3I)+GPS定位精度相当, 在U方向上定位精度前者较后者有了明显的提升, 提升了17.2%, 组合系统新频点收敛时间20.1min比旧频点提升了17.6%. 相似文献
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