旋转载体多天线对GPS卫星可见性分析

利用GPS测量高动态旋转载体飞行轨迹时,一般采用多个天线实现对GPS卫星的连续覆盖。如何选取合理的天线数,在增强天线覆盖特性和降低接收机设计的复杂性等方面达到最优,需要进行分析计算。在综合分析卫星仰角、GPS天线增益以及空间载体旋转对GPS卫星可见性影响的基础上,采用一种新的卫星可见性判断方法,仿真验证了不同天线数在载体旋转条件下对GPS卫星的连续覆盖特性,给出了适用于旋转载体弹道测量的合理的天线数目,具有一定的工程实用意义。     

影响精密单点定位收敛速度的因素分析

分析了接收机类型、测站地理位置及卫星PDOP值三个因素对精密单点定位收敛速度的影响。结果表明,不同类型的接收机对PPP收敛速度有一定影响,但效果并不明显,纬度差异及PDOP值大小对PPP收敛速度的影响较为显著。     

风云3C增强北斗定轨试验结果与分析

首次搭载GPS/BDS双模接收机全球导航卫星掩星探测仪(GNOS)的风云三号C星于2013年9月23日的成功发射,为研究低轨卫星对BDS定轨增强提供了便利。本文首先对低轨卫星GNOS搭载的GPS/BDS双模接收机的观测数据进行统计,并分析了伪距测量精度。然后在全球测站、区域测站两种布局情况下,对无GNOS的BDS单系统定轨、无GNOS的GPS/BDS双系统定轨、有GNOS的BDS单系统定轨增强、有GNOS的GPS/BDS双系统定轨增强4种方案进行北斗轨道及钟差比较分析。结果表明,GNOS对北斗卫星轨道增强在全球测站下,GEO卫星切向精度提升最为显著,提升程度达60%,其次是法向和其他类型卫星切向,部分弧段个别GEO卫星径向精度稍有下降。双系统定轨增强中可视弧段钟差重叠精度RMS值有0.1ns量级改善。7个国内测站区域监测网的定轨试验中对轨道进行了预报,结果表明GNOS对北斗GEO卫星轨道预报精度切向提升达85%,其余方向及卫星有较大改善,平均21.7%。可视弧段钟差重叠精度RMS值有0.5ns量级改善。     

机载DME设备对GPS/L5接收机的干扰分析

探讨了机栽DME设备对GPS/L5接收机的电磁干扰状况.通过分析机载DMECW脉冲信号的发射功率、GPS接收机天线与DME天线之间隔离度等重要参数,计算出不同隔离度时CW干扰功率与接收机容许值之间的差异,认为GPS/L5能克服隔离度较大时的CW干扰,而隔离度较小时干扰功率超过容许值.     

北斗卫星伪距码偏差特性及其影响分析

在北斗导航卫星伪距码偏差特性分析的基础上,建立了倾斜地球同步轨道卫星（IGSO）和中轨卫星（MEO）的伪距码偏差多项式改正模型;并利用星间单差宽巷小数周一致性,分析建立北斗地球同步轨道卫星（GEO）卫星伪距码偏差改正模型。采用武汉大学北斗试验网、中国陆态网络和MGEX网不同位置、不同类型接收机观测数据进行分析验证,结果表明,北斗卫星伪距码偏差特性与观测值频率、卫星类型相关,所有GEO和IGSO卫星变化规律相同,所有MEO卫星变化规律相同,与接收机类型、测站位置和观测时间无关,偏差值大小随卫星高度角变化,其变化规律稳定,可以采用建立的两类改正模型（GEO/IGSO和MEO）进行修正。通过偏差修正后的伪距无电离层组合的残差、双频SPP以及单频PPP三个方面验证了伪距码偏差改正模型的正确性。     

GNSS时差及其在多系统组合定位中的应用

随着卫星导航系统的发展及不断升级,越来越多的GNSS测站开始配备多模GNSS接收机。一方面,多模接收机的应用能够跟踪更多的GNSS卫星,从而改善观测几何条件,提高定位精度和可靠性;另一方面,不同GNSS导航系统采用不同的系统时间定义,存在着系统时差,从而多模GNSS接收机对于不同导航系统卫星的观测值存在着相应的偏差。为实现GNSS系统的兼容与互操作,各个GNSS导航系统目前都提出了系统时差监测的要求。基于此,研究GNSS系统时差的监测及其在多模定位中的应用。首先介绍目前导航系统时差监测的几种方法;然后分析GPS/GLONASS系统时差以及相对硬件延迟的特性;最后将GPS/GLONASS系统时差应用到多模用户导航定位,并详细讨论GPS/GLONASS时差及测站硬件延迟对导航定位的影响。     

导航卫星系统功率增强技术与覆盖范围研究

基于国内外导航卫星功率增强设计的研究,在系统层面上仿真分析我国导航卫星系统中的GEO卫星在不同的仰角下天线波束的地面覆盖区域。在对功率增强技术分析的基础上,着重研究我国导航卫星系统的功率增强信号的覆盖范围,给出10 dB、15 dB、20 dB、25 dB不同功率增强要求下,地面接收功率、天线波束覆盖范围的仿真分析,提出功率增强要求对于卫星的约束条件。并从地面接收信号强度、功率增强的覆盖范围、功率增强技术的实现难度、导航卫星系统的多普勒碰撞问题方面进行的我国导航卫星系统与GPSⅢ系统性能对比。     

GPS天线相位偏心差与卫星高度角对长基线的影响

利用GPS数据处理软件Bernese,通过对8个IGS站在不同卫星高度角下的观测值进行接收机天线相位中心改正前后的长基线解算,分析在不同卫星高度角下,天线相位偏心差对长基线的影响情况。结果表明,对于长基线,采用天线指向北方向的方法仍不能完全消除天线相位偏心差造成的误差影响,因此该因素必须在数据处理中加以考虑。     

GPS天线相位中心改正方法研究

由于天线本身的特性及机械加工等原因,GPS卫星和接收机天线相位中心与其几何中心不重合,从而产生相位中心偏差。某些类型的天线该偏差甚至可达数cm,直接影响高精度GPS测量的精确可靠性[1]。讨论了GAMIT软件在高精度GPS数据处理中进行天线相位中心改正的原理、方法和策略,结合美国IGS观测站及南加州区域站观测数据,对改正方法及策略进行了实验对比与分析。结果表明:对接收机天线相位中心和卫星天线相位中心采用模型改正,而卫星天线相位中心偏移不改正,所得到的基线解算结果较好[2];地面接收机天线方位角的变化对U方向的基线解算结果有较大影响,在高精度GPS测量中,必须进行天线方位角的变化改正。     

GPS天线相位中心垂直分量偏差检测

采用室外天线测定法,对Topcon,Astech,Leica3种类型、4种型号的GPS接收机天线进行了组合实验。进行数据处理后,利用"交换天线法"分别计算出了各种组合天线之间的相位中心垂直分量偏差的差值,进一步分析不同GPS天线组合其相位中心在垂直方向上偏差之差的一致性变化,再简要阐述"高差法"的思想;最后,对开展高精度GPS高程测量工作提出了一些建议。     

利用PPP分析GPS天线积雪引起的信号传播延迟

分析了GPS天线积雪对载波信号场强、功率的影响,推导了载波信号传播延迟的简化计算公式,利用精密单点定位(PPP)计算了测站在GPS天线积雪产生和消除前后的单日解。结果显示,天线积雪使得天线相位中心产生偏移,对平面和高程方向的影响为数个cm,甚至更大。     

GPS卫星和接收机天线绝对PCO、PCV对高精度基线解算的影响分析

在高精度GPS卫星导航数据处理中,卫星和接收机天线的PCO和PCV作为重要的误差来源之一,必须予以改正。本文从高精度基线解算入手,分析了卫星和接收机天线PCO和PCV中各项对高精度基线解算结果的影响。试验结果表明,接收机天线PCO、PCV对长基线或超长基线在各分量方向或长度上的影响最大可达到101 mm。卫星天线PCO、PCV对长基线在各分量方向或长度上的影响在毫米水平,最大不超过4 mm;对超长基线在各分量方向或长度上的影响最大可达到40 mm。     

GPS接收机多路径性能分析

由中国矿业大学文昌校区主楼顶站点实测数据,对GPS接收机的多路径效应进行了分析。由于GPS卫星的运行周期为12个恒星时,则连续两天到达同一位置会提前。根据多路径效应和接收机周围环境,以及卫星特定时间位置有关这一规律,通过对连续两天多路径改正值的相关性进行分析,理论与实验验证表明连续两天GPS卫星到达同一位置提前时间为236 s。     

GPS天线转动测试系统的设计与应用

介绍了用于检测GPS接收机动态性能的天线转动测试系统,分析了天线圆周转,动引起的多普勒频移变化规律,提出了利用多普勒频移反推卫星仰角的基本方法,同时给出了利用该转动测试系统在检验GPS接收机动态测量精度和跟踪性能等方面的实际应用。     

Generation of a consistent absolute phase-center correction model for GPS receiver and satellite antennas

The development and numerical values of the new absolute phase-center correction model for GPS receiver and satellite antennas, as adopted by the International GNSS (global navigation satellite systems) Service, are presented. Fixing absolute receiver antenna phase-center corrections to robot-based calibrations, the GeoForschungsZentrum Potsdam (GFZ) and the Technische Universität München reprocessed more than 10 years of GPS data in order to generate a consistent set of nadir-dependent phase-center variations (PCVs) and offsets in the z-direction pointing toward the Earth for all GPS satellites in orbit during that period. The agreement between the two solutions estimated by independent software packages is better than 1 mm for the PCVs and about 4 cm for the z-offsets. In addition, the long time-series facilitates the study of correlations of the satellite antenna corrections with several other parameters such as the global terrestrial scale or the orientation of the orbital planes with respect to the Sun. Finally, completely reprocessed GPS solutions using different phase-center correction models demonstrate the benefits from switching from relative to absolute antenna phase-center corrections. For example, tropospheric zenith delay biases between GPS and very long baseline interferometry (VLBI), as well as the drift of the terrestrial scale, are reduced and the GPS orbit consistency is improved.     

GPS接收机天线相位中心偏差的三维检定研究

根据GPS接收机天线相位中心的几何关系，在超短基线相对定位法的基础上，利用旋转天线，结合精密水准测量，给出了一种天线相位中心偏差三雏检验的方法。实例表明，该方法具有较高的精度和可靠性，适合于在野外对GPS接收机天线相位中心偏差进行实际检定。     

多GNSS系统精密定轨ISB/IFB估计及特性分析

多全球导航卫星系统（Global Navigation Satellite System,GNSS）系统联合精密定轨需要考虑系统间及频率间偏差的影响。推导了多GNSS定轨系统间偏差（inter system bias,ISB）/频率间偏差（inter frequency bias,IFB）解算模型,以GPS系统硬件延迟为基准,给出了一种消除ISB/IFB秩亏的约束方法。试验数据结果表明,各系统ISB/IFB均表现出良好的稳定性及同一系统各卫星时间序列的一致性,BDS ISB的标准差为0.36 ns,Galileo ISB的标准差为0.18 ns,GLONASS IFB的标准差为0.51 ns;在接收机类型相同的情况下,不同跟踪站的ISB比较接近,但仍可达到ns级差异;GLONASS IFB在同一跟踪站相同频道号的卫星及不同跟踪站相同频道号卫星均表现出了良好的一致性。     

Improved antenna phase center models for GLONASS

Thanks to the increasing number of active GLONASS satellites and the increasing number of multi-GNSS tracking stations in the network of the International GNSS Service (IGS), the quality of the GLONASS orbits has become significantly better over the last few years. By the end of 2008, the orbit RMS error had reached a level of 3–4 cm. Nevertheless, the strategy to process GLONASS observations still has deficiencies: one simplification, as applied within the IGS today, is the use of phase center models for receiver antennas for the GLONASS observations, which were derived from GPS measurements only, by ignoring the different frequency range. Geo++ GmbH calibrates GNSS receiver antennas using a robot in the field. This procedure yields now separate corrections for the receiver antenna phase centers for each navigation satellite system, provided its constellation is sufficiently populated. With a limited set of GLONASS calibrations, it is possible to assess the impact of GNSS-specific receiver antenna corrections that are ignored within the IGS so far. The antenna phase center model for the GLONASS satellites was derived in early 2006, when the multi-GNSS tracking network of the IGS was much sparser than it is today. Furthermore, many satellites of the constellation at that time have in the meantime been replaced by the latest generation of GLONASS-M satellites. For that reason, this paper also provides an update and extension of the presently used correction tables for the GLONASS satellite antenna phase centers for the current constellation of GLONASS satellites. The updated GLONASS antenna phase center model helps to improve the orbit quality.     

Estimation of phase center corrections for GLONASS-M satellite antennas

Driven by the comprehensive modernization of the GLONASS space segment and the increased global availability of GLONASS-capable ground stations, an updated set of satellite-specific antenna phase center corrections for the current GLONASS-M constellation is determined by processing 84 weeks of dual-frequency data collected between January 2008 and August 2009 by a worldwide network of 227 GPS-only and 115 combined GPS/GLONASS tracking stations. The analysis is performed according to a rigorous combined multi-system processing scheme providing full consistency between the GPS and the GLONASS system. The solution is aligned to a realization of the International Terrestrial Reference Frame 2005. The estimated antenna parameters are compared with the model values currently used within the International GNSS Service (IGS). It is shown that the z-offset estimates are on average 7 cm smaller than the corresponding IGS model values and that the block-specific mean value perfectly agrees with the nominal GLONASS-M z-offset provided by the satellite manufacturer. The existence of azimuth-dependent phase center variations is investigated and uncertainties in the horizontal offset estimates due to mathematical correlations and yaw-attitude modeling problems during eclipse seasons are addressed. Finally, it is demonstrated that the orbit quality benefits from the updated GLONASS-M antenna phase center model and that a consistent set of satellite antenna z-offsets for GPS and GLONASS is imperative to obtain consistent GPS- and GLONASS-derived station heights.