风云三号C星GNOS北斗掩星电离层探测初步结果

利用风云三号卫星C星GNOS掩星探测仪电离层数据,分析了2013年10月FY-3C GNOS探测的北斗掩星电离层廓线分布,将2013年10月1日至2015年10月10日期间FY-3C GNOS观测的F₂层峰值电子密度（N_mF₂）与地面电离层测高仪观测结果进行对比,验证了FY-3C GNOS北斗电离层掩星的探测精度.结果表明,FY3-C GNOS北斗电离层掩星与电离层测高仪探测的N_mF₂数据相关系数为0.96,平均偏差为10.21%,标准差为19.61%.在不同情况下其数据精度有如下特征:白天精度高于夜晚;夏季精度高于分季,分季精度高于冬季;中纬地区精度高于低纬地区,低纬地区精度高于高纬地区; BDS倾斜同步轨道（IGSO）卫星精度高于同步轨道（GEO）卫星和中轨道（MEO）卫星.FY-3C GNOS北斗电离层掩星与国际上其他掩星电离层数据精度的一致性对GNSS掩星探测资料的综合利用具有重大意义.      

GRO和LRO掩星事件模拟研究

GRO（Global Navigation Satellite System Radio Occultation）和LRO（Low Earth Orbit Radio Occultation）联合组网探测地球大气是无线电掩星探测技术的主要发展方向.本文根据掩星事件的数学判据,仿真分析了LEO卫星主要轨道参数对GRO和LRO掩星事件数量和全球分布情况的影响.研究表明:卫星轨道越低GRO掩星事件越多;轨道倾角在30°和75°之间时,GRO掩星事件较多,全球覆盖率也较大;利用极轨卫星进行LRO掩星探测时,LRO掩星事件较均匀地分布在各纬度带.研究成果对GRO和LRO联合星座设计具有参考价值.      

LEO卫星轨道误差对无线电掩星反演大气参数的影响

采用数值方法估计了LEO卫星轨道误差对无线电掩星反演大气参数的影响。并将其应用于1995年10月11日的某次掩星事件的观测资料处理和分析，得到了LEO卫星轨道误差对无线电掩星反演大气参数影响的定量结果。     

掩星大气探测系统误差源分析

根据掩星大气探测反演原理,研究了影响系统产品精度的误差源,并对多普勒观测误差、天线相位中心变化误差、多路径误差、卫星质心变化误差、导航卫星钟飘、卫星姿态变化误差和精密定轨速度误差进行分析,根据工程实现可行性提出了系统误差分配建议,为掩星大气探测系统设计提供参考.      

FY-3D卫星的北斗掩星分布特征与误差特性

利用2018年1－3月FY-3D卫星的掩星折射率数据,研究了北斗导航卫星系统的掩星分布特点、数据精度以及误差统计特征。北斗导航卫星系统同步静止轨道掩星沿卫星轨道呈弧状分布在南北两极地区,倾斜轨道掩星在东西半球低纬度地区分别形成一小一大两个空洞,中地球轨道掩星则全球均匀分布。北斗掩星折射率数据精度在探测核心区域,即12~32 km范围内,与ERA5再分析资料计算的折射率相比,平均偏差的标准差约为1.5%,在核心区外,标准差从1.5%逐渐增大到6%。静止轨道掩星的平均偏差在高层略大于倾斜轨道和中地球轨道掩星。下降掩星在20 km以上区域的标准差大于上升掩星,20 km以下区域小于上升掩星。高纬地区北斗掩星标准差最小,低纬地区最大,对流层中下层尤其明显。分析结果表明,北斗掩星的数据精度和误差特征与GPS掩星数据相似。      

基于X射线掩星探测反演行星大气密度

X射线掩星是一种常见的天文现象，基于X射线掩星探测的大气密度反演是一种涉及学科交叉的新方法，其通过处理高能X射线天体辐射源的掩星观测数据实现大气密度的反演，基本原理为X射线在大气中传播时，X射线光子被大气中的原子（包括分子中的原子）吸收和散射，从而导致X射线强度发生衰减，根据衰减后X射线信号的强度反演对应的密度廓线。本文根据X射线掩星探测的应用需求，论证了基于X射线掩星实现大气密度反演的新方法，重点介绍了光变曲线拟合和能谱拟合两种地球中高层大气密度反演算法，分析了X射线掩星探测反演大气密度的研究进展和研究方法，对基于X射线掩星反演大气密度的优点进行分析和讨论，进而对X射线掩星探测的应用场景进行展望。结果表明，作为一种新型中高层大气密度测量手段，X射线掩星探测可对中高层大气密度实现有效探测，弥补了目前中高层大气密度实测数据的不足。     

不规则区域成像覆盖星座构型优化设计

近年来卫星对地观测需要呈现逐年上升趋势.从单个目标点的对地观测卫星星座构型设计方法入手,推广为设计满足不规则大范围成像区域重访时间需求的卫星星座.以卫星数目最少及满足重访时间要求为优化目标,采用改进的模拟退火算法,结合改进的等面积网格点覆盖法,提出了一种针对不规则区域成像全覆盖的卫星星座构型优化设计方法.分析了光照因素对重访时间、所需卫星数目以及星座构型的影响,并通过仿真分析验证了算法的可行性.      

GNSS外辐射源雷达低慢小目标探测概率

尽管全球导航卫星系统(GNSS)外辐射源雷达具有信号源广泛、覆盖率高、容易进行时间同步等特点，受到了国内外研究机构的广泛关注，但由于卫星位置变化和单颗卫星的目标探测性能有限，难以满足实际探测需求。根据几何构型给出GNSS外辐射源雷达双基地角计算方式，仿真研究双基地角与目标雷达散射截面积(RCS)的关系，分析探测时间与目标最大探测距离的关系，得到目标探测概率的理论表达式，并据此评估基于GPS L5信号的外辐射源雷达在单星、多源融合及前后向协同探测模式的目标探测概率。仿真结果表明：单星前向和后向探测模式的有效探测时间覆盖率不足1%，采用前后向协同及多源融合的探测方式，可有效提升GNSS外辐射源雷达的目标探测性能至25%；通过采用连续扫描检测的方式实时改变接收天线的照射方向进行目标探测，在前后向协同的多源融合探测模式下，有效探测时间覆盖率达到98.96%，基本满足全天时有效探测需求。     

欧洲将发射首颗极轨气象卫星

□□2006年6月,欧洲将用俄罗斯联盟号火箭发射气象业务-1(METOP-1)卫星,它是欧洲首颗极轨气象卫星.卫星上安装的新一代科学仪器将为气象学家和天气预报者提供更准确的天气遥感数据,包括温度和湿度测量数据、风速和风向(尤其是海洋上)测量数据及大气中臭氧剖面等.     

基于覆盖性能的Walker-δ星座构型保持

考虑到Walker-δ星座中各星相互协作关系,提出一种基于覆盖性能的星座构型保持策略.作为策略判别指标的覆盖性能由一种改进的网格点仿真法获取.这种改进方法依照卫星星下点与网格点的几何关系,可以快速判断处于覆盖区的网格点,然后统计出星座的全球覆盖信息.卫星的标称位置是考虑J2项摄动长期影响得到的动态位置.星座运行过程中,一旦发现不满足覆盖要求的点,结合各卫星的标称位置,可以找出影响覆盖性能的卫星.最后将该卫星调整到标称位置即可完成构型保持.最后给出构型保持策略的仿真算例,仿真结果表明了策略的有效性.     

The impact on tsunami detection from space using GNSS-reflectometry when combining GPS with GLONASS and Galileo

The devastating Sumatra tsunami in 2004 demonstrated the need for a tsunami early warning system in the Indian Ocean. Such a system has been installed within the German-Indonesian Tsunami Early Warning System (GITEWS) project. Tsunamis are a global phenomenon and for global observations satellites are predestined. Within the GITEWS project a feasibility study on a future tsunami detection system from space has therefore been carried out. The Global Navigation Satellite System Reflectometry (GNSS-R) is an innovative way of using GNSS signals for remote sensing. It uses ocean reflected GNSS signals for sea surface altimetry. With a dedicated Low Earth Orbit (LEO) constellation of satellites equipped with GNSS-R receivers, densely spaced sea surface height measurements could be established to detect tsunamis. Some general considerations on the geometry between LEO and GNSS are made in this simulation study. It exemplary analyzes the detection performance of a GNSS-R constellation at 900 km altitude and 60° inclination angle when applied to the Sumatra tsunami as it occurred in 2004. GPS is assumed as signal source and the combination with GLONASS and Galileo signals is investigated. It can be demonstrated, that the combination of GPS and Galileo is advantageous for constellations with few satellites while the combination with GLONASS is preferable for constellations with many satellites. If all three GNSS are combined, the best detection performance can be expected for all scenarios considered. In this case an 18 satellite constellation will detect the Sumatra tsunami within 17 min with certainty, while it takes 53 min if only GPS is considered.     

FY-3 Meteorological Satellites and the Applications

FY-3 is the second generation polar-orbiting meteorological satellite of China. The first satellite named FY-3A of this series was launched on 27 May 2008. The first operational satellite named FY-3C of this series was launched on 23 September, 2013. The new generation satellites are to provide three-dimensional, quantitative, multi-spectral global remote sensing data under all weather conditions, which will greatly help the operational numerical weather prediction, global climate change research, climate diagnostics and prediction, and natural disaster monitoring. They will also provide help for many other fields such as agriculture, forestry, oceanography and hydrology. With the abovementioned capability, the FY-3 satellites can make valuable contributions to improving weather forecasts, global natural-disaster and environmental monitoring.      

基于覆盖圆的太阳同步回归轨道卫星目标轨迹调整方法

遥感卫星星座在环境监测、地理测绘等领域运用中,需要考虑目标轨迹分布的优化问题.轨迹分布与星座的重访能力和进出站间隔保持等应用需求密切相关.目前对星下点轨迹分布的优化和调整还缺乏准确实用的方法,存在卫星数目增多带来的计算量增加问题和对多种需求综合考虑不够的问题.为了克服现有技术的不足,解决太阳同步回归轨道遥感卫星星座的目...     

太阳系天体引力对空间引力波探测日心编队构型的影响分析

针对太极空间引力波探测任务，建立了太阳系天体引力摄动对日心编队构型影响的数学模型，利用仿真手段分析了太阳系中行星和月球、矮行星和小行星引力摄动对空间引力波探测日心编队构型的影响，提出了一种综合考虑小行星到卫星轨道距离和星等的二重筛选方法，能够快速估计小行星相对加速度的上界.分析了日心编队构型卫星初始相位角变化对太阳系天体引力摄动的影响.仿真结果表明，在行星和月球中，地球、金星和木星引力对空间引力波探测编队构型影响较大，行星和月球的引力叠加影响达到-2.78×10-11km·-2.矮行星的引力叠加影响不大于1.25×10-17km·-2，小行星引力的叠加影响不大于1.1180×10-15km·-2.另外，编队卫星受到的太阳系天体引力摄动对编队构型卫星初始相位角的变化不敏感.      

Geosynchronous satellites expanding a future GNSS satellite constellation: A precise orbit determination study

The integration of geosynchronous orbit (GSO) satellites in Global Navigation Satellite Systems (GNSS) is mostly discussed to enable a regional enhancement for tracking. But how do GSO satellites affect the orbit determination of the rest of the constellation? How accurately can these orbits be determined in a future GNSS tracking scenario with optical links? In this simulation study we analyze the benefit of GSO satellites as an expansion of a MEO (Medium Earth Orbit) satellite constellation – we selected the Galileo satellite constellation – for MEO Precise Orbit Determination (POD). We address not only the impact on POD of MEO satellites but also the possibility to precisely determine the GSO satellites – geostationary orbits (GEO) and inclined geosynchronous orbits (IGSO) – in such an expanded MEO constellation. In addition to GNSS microwave observations, we analyze the influence of different optical links between the participating entities: Optical two-way Inter-Satellite Links (OISL) and ground-space oriented Optical Two-Way Links (OTWL). These optical measurements together with the GNSS microwave observations give a remarkable benefit for the POD capability. In the case of GNSS and OTWL, we simulate the measurements with regard to a network of 16 ground stations. We pay great attention to the simulation of systematic effects of all measurement techniques. We discuss the influence on the systematic errors as well as the formal orbit uncertainties. A MEO constellation expanded with GSO satellites as well as the use of optical links together with GNSS observations not only improves the MEO satellite orbits but also the GSOs to a great extent.     

基于帝国竞争优化的双目标综合决策选星算法

全球卫星导航系统（GNSS）的应用前景已经得到世界各国的普遍承认，其应用领域也趋于多样化，在此背景下，卫星接收机也要求其具有更快的解算速度和可靠的精度。针对目前多数接收机的选星算法都是固定选星数目从而限制算法机动性的问题，提出基于帝国竞争优化算法（ICA）的双目标综合决策选星算法。为了更好获取几何构型较好的卫星星座，引入可见卫星的卫星仰角和方向角先验信息，进行先验性约束，通过构建几何精度因子（GDOP）以及选星数目2个目标，进行综合决策的快速选星，提高了选星的灵活度，并且在满足用户精度的要求下减轻了多星座卫星接收机的计算负担。通过仿真实验和实测数据对双目标综合决策选星算法验证的结果表明:所提算法在高度截止角5°下引入先验性约束条件后平均选星数目在仿真数据和实测数据中缩减率分别为51.8%和45.4%，平均GDOP值较无约束下分别减少0.209 2和0.248 4。同时，所提算法单次选星平均耗时分别为0.168 4 s和0.303 1 s，与遍历法的选星耗时4 s相比，提高了95.79%和92.42%。      

Progress for Spaceborne Microwave Remote Sensing in China

In this paper,technological progress for China's microwave remote sensing is intro-duced.New developments of the microwave remote sensing instruments for meteorological satellite FY-3,ocean dynamic measurement satellite(HY-2),environment small SAR satellite(HJ-1C) and China's lunar exploration satellite(Chang'E-1),geostationary orbit meteorological satellite FY-4M,are reported.      

Evaluation and analysis on positioning performance of BDS/QZSS satellite navigation systems in Asian-Pacific region

By using the observation data and products of precise obit and clock offset from Multi-GNSS Experiment (MGEX) of the International GNSS Service (IGS) and GNSS Research Centre, Curtin University in this paper, the positioning performance of BDS/QZSS satellite navigation system has been analyzed and evaluated in aspects of the quantity of visible satellites, DOP value, multipath effect, signal-to-noise ratio, static PPP and kinematic PPP. The analysis results show that compared to BDS single system when the cutoff angle are 30°and 40°, the DOP value of BDS/QZSS combined system has decreased above 20%, and the quantity of visible satellites increased about 16–30% respectively, because of the improved spatial geometric configuration. The magnitude of satellite multipath effect of BDS system shows the trend of MEO?>?IGSO?>?GEO, which is consistent with that of QZSS satellite system, as the constellation structure of the two systems is similar. The variation tendencies of signal-to-noise ratio with respect to elevation angle of the two systems are almost the same at all frequencies, showing that at the same elevation angle the signal-to-noise ratio of MEO satellites is higher than that of IGSO satellites, as the higher obit is the lower transmitting power is obtained. For having a specially designed obit, the variation of signal-to-noise ratio of BDS system is more stable. However, the magnitude of signal-to-noise ratio of QZSS system appears the trend of frequency 3?>?frequency 2?>?frequency 1. The static PPP performance of the BDS/QZSS combination system has been improved more significantly than the BDS single system in E, N and U directions. When the cutoff angle are at 7°, 15° and 30°, the PPP accuracy is increased about 25–34% in U direction, 10–13% and 23–34% in E and N directions respectively. When the elevation angle is large (40°), compared to BDS single system at lower elevation angles (7° and 15°) the PPP accuracy of the BDS/QZSS combination system is improved above 30% in U direction. In kinematic PPP performance, compared to BDS single system, the accuracy, availability and reliability of the BDS/QZSS combination system has been improved too, especially at large elevation angles (30° and 40°), the kinematic PPP accuracy in E and U directions has been improved about 10–50%, and above 50% in U direction. It can be concluded that the combination with QZSS system can improve the positioning accuracy, reliability and stability of BDS system. In the future, with the improvement of the satellite construction of Japan’s QZSS system and the global networking of China’s BDS satellites, the QZSS satellites will contribute greatly to improve the positioning accuracy, reliability, availability and stability of GNSS systems in areas such as cities, mountains, densely-packed buildings and severely covered areas in Asian-Pacific region.     

Minimum of PDOP and its applications in inter-satellite links (ISL) establishment of Walker-δ constellation

Within the next decade, there will be a number of GNSS (Global Navigation Satellite System) available, i.e. modernized GPS, Galileo, restored GLONASS, BeiDou and many other regional GNSS augmentation systems. Thus, measurement redundancies and geometry of the satellites can be improved. GDOP (Geometric Dilution of Precision) and PDOP (Position Dilution of Precision) are associated with the constellation geometry of satellites, and they are the geometrically determined factors that describe the effect of geometry on the relationship between measurement error and position error. GDOP and PDOP are often used as standards for selecting good satellites to meet the desired positioning precision. In this paper, the related conclusions of minimum of GDOP which was discussed are given, and it is used to study the minimum of PDOP for two cases that the receiver is on the earth’s surface and the receiver is on satellite. The corresponding theorem and constructive solutions of minimum of PDOP are given. Then, the rationality of the ISL (inter-satellite link) establishment criteria in Walker-δ constellation is discussed by using the theory of minimum of PDOP. Finally, the minimum of PDOP is calculated when the number of satellites is 4–10, and these results are verified by using Monte Carlo method.     

Technology Progress Report for Microwave Remote Sensing

In this presentation, technological progress for China's microwave remote sensing is introduced. New developments of the microwave remote sensing instruments for China's lunar exploration satellite (Chang'E-1), meteorological satellite FY-3 and ocean dynamic measurement satellite (HY-2) are reported.