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| 1 | Orbit determination and time synchronization for a GEO/IGSO satellite navigation constellation with regional tracking network显示文摘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 obtained by simultaneously processing both tracking data and TS data.Consequently,inconsistency between tracking system and TS system caused by remaining instrumental errors not calibrated may decrease navigation accuracy.On the other hand,POD for the mixed constellation of GEO/IGSO/MEO with the regional tracking network leads to parameter estimations that are highly correlated.Notorious example of correlation is found between GEO's orbital elements and its clock errors.We estimate orbital elements and clock errors for a 3GEO+2IGSO constellation in this study using a multi-satellite precise orbit determination (MPOD) strategy,with which clock error elimination algorithm is applied to separate orbital and clock estimates to improve numerical efficiency.Satellite Laser Ranging (SLR) data are used to evaluate User Ranging Error (URE),which is the orbital error projected on a receiver's line-of-sight direction.Two-way radio-wave time transfer measurements are used to evaluate clock errors.Experimenting with data from the regional tracking network,we conclude that the fitting of code data is better than 1 m in terms of Root-Mean-Square (RMS),and fitting of carrier phase is better than 1 cm.For orbital evaluation,difference between computed receiver-satellite ranging based on estimated orbits and SLR measurements is better than 1 m (RMS).For clock estimates evaluation,2-hour linear-fitting shows that the satellite clock rates are about 1.E-10 s/s,while receiver clock rates are about 1×10 13-1×10 12 s/s.For the 72-hour POD experiment,the average differences between POD satellite clock rates estimates and clock measurements based on TS system are about 1×10 13 s/s,and for receiver clock rates,the differences are about 1×10 15 s/s. | ZHOU ShanShi HU XiaoGong WU Bin LIU Li QU WeiJing GUO Rui HE Feng CAO YueLing Wu XiaoLi ZHU LingFeng SHI Xin TAN HongLi | 2011 | Science China(Physics,Mechanics & Astronomy)2011，54，6： | 44 |
| 2 | Multipath error detection and correction for GEO/IGSO satellites显示文摘Constellations of regional satellite navigation systems are usually constituted of geostationary satellites (GEO) and inclined geostationary satellites (IGSO) for better service availability. Analysis of real data shows that the pseudorange measurements of these two types of satellites contain significant multipath errors and code noise, and the multipath for GEO is extremely serious, which is harmful to system services. In contrast, multipath error of carrier phase measurements is less than 3 cm, which is smaller than the multipath of pseudorange measurements by two orders of magnitude. Using a particular combination of pseudorange and dual-frequency carrier phase measurements, the pseudorange multipath errors are detected, and their time varying features are analyzed. A real-time multipath correction algorithm is proposed in this paper, which is called CNMC (Code Noise and Multipath Correction). The algorithm decreases the influence of the multipath error and therefore ensures the performance of the system. Data processing experiments show that the multipath error level may be reduced from 0.5 m to 0.15 m by using this algorithm, and 60% of GEO multipath errors and 42% of IGSO multipath errors are successfully corrected with CNMC. Positioning experiments are performed with a constellation of 3 GEO plus 3 IGSO satellites. For dual-frequency users the East-West position accuracy is improved from 1.31 m to 0.94 m by using the CNMC algorithm, the South-North position accuracy is improved from 2.62 m to 2.29 m, and the vertical position accuracy is improved from 4.25 m to 3.05 m. After correcting multipath errors, the three-dimensional position accuracy is improved from 5.16 m to 3.94 m. | WU XiaoLi ZHOU JianHua WANG Gang HU XiaoGong CAO YueLing | 2012 | Science China(Physics,Mechanics & Astronomy)2012，55，7： | 31 |
| 3 | Positioning accuracy assessment for the 4GEO/5IGSO/2MEO constellation of COMPASS显示文摘Determined to become a new member of the well-established GNSS family,COMPASS(or BeiDou-2) is developing its capabilities to provide high accuracy positioning services.Two positioning modes are investigated in this study to assess the positioning accuracy of COMPASS' 4GEO/5IGSO/2MEO constellation.Precise Point Positioning(PPP) for geodetic users and real-time positioning for common navigation users are utilized.To evaluate PPP accuracy,coordinate time series repeatability and discrepancies with GPS' precise positioning are computed.Experiments show that COMPASS PPP repeatability for the east,north and up components of a receiver within China's Mainland is better than 2 cm,2 cm and 5 cm,respectively.Apparent systematic offsets of several centimeters exist between COMPASS precise positioning and GPS precise positioning,indicating errors remaining in the treatments of COMPASS measurement and dynamic models and reference frame differences existing between two systems.For common positioning users,COMPASS provides both open and authorized services with rapid differential corrections and integrity information available to authorized users.Our assessment shows that in open service positioning accuracy of dual-frequency and single-frequency users is about 5 m and 6 m(RMS),respectively,which may be improved to about 3 m and 4 m(RMS) with the addition of differential corrections.Less accurate Signal In Space User Ranging Error(SIS URE) and Geometric Dilution of Precision(GDOP) contribute to the relatively inferior accuracy of COMPASS as compared to GPS.Since the deployment of the remaining 1 GEO and 2 MEO is not able to significantly improve GDOP,the performance gap could only be overcome either by the use of differential corrections or improvement of the SIS URE,or both. | ZHOU ShanShi CAO YueLing ZHOU JianHua HU XiaoGong TANG ChengPan LIU Li GUO Rui HE Feng CHEN JunPing WU Bin | 2012 | Science China(Physics,Mechanics & Astronomy)2012，55，12： | 31 |
| 4 | Orbit determination for Chang'E-2 lunar probe and evaluation of lunar gravity models显示文摘The Unified S-Band(USB) ranging/Doppler system and the Very Long Baseline Interferometry(VLBI) system as the ground tracking system jointly supported the lunar orbit capture of both Chang'E-2(CE-2) and Chang'E-1(CE-1) missions.The tracking system is also responsible for providing precise orbits for scientific data processing.New VLBI equipment and data processing strategies have been proposed based on CE-1 experiences and implemented for CE-2.In this work the role VLBI tracking data played was reassessed through precision orbit determination(POD) experiments for CE-2.Significant improvement in terms of both VLBI delay and delay rate data accuracy was achieved with the noise level of X-band band-width synthesis delay data reaching 0.2-0.3 ns.Short-arc orbit determination experiments showed that the combination of only 15 min's range and VLBI data was able to improve the accuracy of 3 h's orbit using range data only by a 1-1.5 order of magnitude,confirming a similar conclusion for CE-1.Moreover,because of the accuracy improvement,VLBI data was able to contribute to CE-2's long-arc POD especially in the along-track and orbital normal directions.Orbital accuracy was assessed through the orbital overlapping analysis(2 h arc overlapping for 18 h POD arc).Compared with about 100 m position error of CE-1's 200 km 200 km lunar orbit,for CE-2's 100 km 100 km lunar orbit,the position errors were better than 31 and 6 m in the radial direction,and for CE-2's 15 km 100 km orbit,the position errors were better than 45 and 12 m in the radial direction.In addition,in trying to analyze the Delta Differential One-Way Ranging(DOR) experiments data we concluded that the accuracy of DOR delay was dramatically improved with the noise level better than 0.1 ns and systematic errors better calibrated,and the Short-arc POD tests with DOR data showed excellent results.Although unable to support the development of an independent lunar gravity model,the tracking data of CE-2 provided evaluations of different lunar gravity models through POD.It is found that for the 100 km 100 km lunar orbit,with a degree and order expansion up to 165,JPL's gravity model LP165P did not show noticeable improvement over Japan's SGM series models(100×100),but for the 15 km×100 km lunar orbit,a higher degree-order model can significantly improve the orbit accuracy. | Li PeiJia Hu XiaoGong Huang Yong Wang GuangLi Jiang DongRong Zhang XiuZhong Cao JianFeng Xin Nan | 2012 | Science China(Physics,Mechanics & Astronomy)2012，55，3： | 30 |
| 5 | Orbit determination of Chang'E-3 and positioning of the lander and the rover显示文摘Chang’E-3 landed on the east of Sinus Iridum area on December 14,2013,performing China’s first successful soft landing on the lunar surface.We present the results on precision orbit determination and positioning of the lander and the rover.We describe the data,modeling,and methods used to achieve position knowledge over the period December 2–21,2014.In addition to the radiometric X-band range and Doppler tracking data,delta differential one-way ranging data are also used in the calculation,which show that they strongly improve the accuracy of the orbit reconstruction.Total position overlap differences are about 20 and 30 m for the 100 km 9 100 km and100 km9 15 km lunar orbit,respectively,increased by*50%with respect to CE-2 and at the same level as other lunar spacecrafts of recent era such as SELENE and lunar reconnaissance orbiter(LRO).The position error of the soft landing trajectory is less than 100 m.A kinematic statistical method is applied to determine the position of the lander and relative position of the rover with respect to the lander.The position difference of the lander is better than50 m compared to LRO photograph result.Compared with the delta very long baseline interferometry(VLBI)group delay between the lander and the rover,the delta VLBI phase delay can improve the relative position of the rover from*1,000 to*1 m. | Yong Huang Shengqi Chang Peijia Li Xiaogong Hu Guangli Wang Qinghui Liu Weimin Zheng Min Fan | 2014 | Chinese Science Bulletin2014，59，29： | 28 |
| 6 | Precise orbit determination for geostationary satellites with multiple tracking techniques显示文摘A new precise orbit determination (POD) strategy based on the combination of satellite laser ranging (SLR) and C-band transfer ranging for geostationary satellites (GEO) is presented.Two approaches to calibrate ranging biases of the C-band ranging system are proposed,namely the two tracking system co-location comparison and the combined POD method,with calibration accuracies estimated to be 0.5 ns and 1 ns respectively.Using data from a C-band tracking network in China,POD experiments indicate that meter-level POD accuracy is achievable for GEO.Root-mean-square (RMS) of the post-fit C-band ranging data is about 0.205 m.The radial component errors of POD are evaluated with SLR data from a station in Beijing,with residual RMS of 0.133 m.Orbital overlapping experiments show the total orbit error is a few meters.Computations of SLR residuals also suggest that for 2-hour prediction,the predicted radial error is about 0.373 m. | GUO Rui HU XiaoGong TANG Bo HUANG Yong LIU Li CHENG LiuCheng HE Feng | 2010 | Chinese Science Bulletin2010，55，8： | 24 |
| 7 | The wide-area difference system for the regional satellite navigation system of COMPASS显示文摘The regional satellite navigation system of COMPASS (Phase I) provides both open services and authorized services. Authorized services offer differential corrections and integrity information to users to support higher positioning, navigation and timing precision. Experimenting with real data, positioning accuracy is estimated with a 3GEO/4IGSO COMPASS constellation. The results show that with dual-frequency and single-frequency pseudo-range measurements, the positioning errors are respectively 8 and 10 m (RMS) for open service users, while for authorized users, the errors are 4 and 5 m (RMS), respectively. The COMPASS constellation geometry may cause large error to occur in the height component by 7-9 m for dualor single-frequency users, which can be effectively reduced with the differential corrections supplied by the authorized services. Multipath errors are identified and corrected for COMPASS, resulting in 25% positioning accuracy improvement for dual-frequency users and 10% improvement for single-frequency users. | CAO YueLing HU XiaoGong WU Bin ZHOU ShanShi LIU Li SU RanRan CHANG ZhiQiao HE Feng ZHOU JianHua | 2012 | Science China(Physics,Mechanics & Astronomy)2012，55，7： | 21 |
| 8 | Improvement of orbit determination for geostationary satellites with VLBI tracking显示文摘China’s COMPASS satellite navigation system consists of five or more geostationary (GEO) satellites.The roles of GEO satellites are to improve the regional user’s positioning accuracy and provide the continuous Radio Determination Satellite Service.The motion of GEO satellites relative to a ground tracking station is almost fixed,and regular orbit maneuvers are necessary to maintain the satellites’ allocated positions above the equator.These features present difficulties in precise orbit determination (POD).C-band ranging via onboard transponders and the L-band pseudo-ranging technique have been used in the COMPASS system.This paper introduces VLBI tracking,which has been successfully employed in the Chinese lunar exploration programs Chang’E-1 and Chang’E-2,to the POD of GEO satellites.In contrast to ranging,which measures distances between a GEO satellite and an observer,VLBI is an angular measurement technique that constrains the satellite’s position errors perpendicular to the satellite-to-observer direction.As a demonstration,the Chinese VLBI Network organized a tracking and orbit-determination experiment for a GEO navigation satellite lasting 24 h.This paper uses the VLBI delay and delay-rate data,in combination with C-band ranging data,to determine the GEO satellite’s orbit.The accuracies of the VLBI delay and delay rate data are about 3.6 ns and 0.4 ps/s,respectively.Data analysis shows that the VLBI data are able to calibrate systematic errors of the C-band ranging data,and the combination of the two observations improves orbit prediction accuracy with short-arc data,which is important for orbital recovery after maneuvers of GEO satellites.With the implementation of VLBI2010,it is possible for VLBI to be applied in the COMPASS satellite navigation system. | HUANG Yong HU XiaoGong ZHANG XiuZhong JIANG DongRong GUO Rui WANG Hong SHI ShanBin | 2011 | Chinese Science Bulletin2011，56，26： | 18 |
| 9 | Orbit determination and prediction accuracy analysis for a regional tracking network显示文摘China's COMPASS satellite navigation system relies on a regional tracking network to provide navigation services. Limited by its geographic border,the regional network is able to cover only 30% of the medium-earth-orbits(MEO). Accuracy of determined and predicted orbits is not able to satisfy system requirements if the tracking data processing strategy for global tracking network processing is used for the regional network. Two major error sources for orbital prediction are accuracy of initial orbital elements and dynamical modeling. To achieve better prediction accuracy,we propose a two-step orbit determination and prediction strategy. For step 1,only solar radiation pressure(SRP) parameters are estimated along with the orbital elements and other parameters; for step 2,all parameters are estimated but the SRP parameters are tightly constrained to their step 1 estimates. Experimenting with data from a regional GPS network,we conclude for orbital prediction using the proposed two-step strategy,the average user range error(URE) for 24-h prediction arcs is better than 0.6 m. | ZHOU ShanShi 1,2,3 ,HU XiaoGong 1 & WU Bin 1 1 Shanghai Astronomical Observatory,Chinese Academy of Sciences,Shanghai 200030,China 2 Graduate University of Chinese Academy of Sciences,Beijing 100049,China 3 Research Center of GNSS,Wuhan 430079,China | 2010 | Science China(Physics,Mechanics & Astronomy)2010，53，6： | 16 |
| 10 | Mars Express tracking and orbit determination trials with Chinese VLBI network显示文摘With strong support from European Space Agency (ESA),Shanghai Astronomical Observatory (SHAO) organized a tracking and orbit determination trails using Chinese VLBI Network (CVN) to track Mars Express,the first Mars probe launched by ESA. Using a high-resolution VLBI software correlator and Doppler measurement system developed in-house,two sets of tracking data,VLBI and Doppler,were acquired. The trials represent the first successful foray held in China to track a probe about 360 million kilometers away from the Earth. The tracking data are analyzed using a Mars satellite orbit determination software system developed at SHAO. The results show that the accuracy of 5 s integrated three-way-Doppler data is about 0.3 mm/s,or roughly the same accuracy as ESA's tracking data. Position discrepancies between the Doppler-based orbit solution of 8 h arc-length (about 1 orbital revolution) and ESA's reconstructed orbit are of the order of several hundred meters. In preparing for the Russia-China co-sponsored Mars exploration mission Phobos-Grunt-YingHuo,simulations were carried out to evaluate the achievable orbital accuracy levels and the contributions of VLBI and Doppler data respectively. Results show that Doppler data provide better orbit accuracy,so that for VLBI to be able to provide kilometer level orbit solutions,the accuracy of VLBI measurement needs to be improved by at least one order of magnitude. | CAO JianFeng HUANG Yong HU XiaoGong MA maoLi ZHENG WeiMin | 2010 | Chinese Science Bulletin2010，55，32： | 14 |
| 11 | SIS accuracy and service performance of the BDS-3 basic system显示文摘On December 27,2018,the basic system of the third-generation BeiDou navigation satellite system(BDS-3)completed the deployment of its constellation of 18 MEO networking satellites as well as the construction of the operation control system(OCS)and began to provide basic navigation services to users worldwide.Compared with BDS-2,BDS-3 aims to offer users better navigation signals and higher precision with a series of new technologies.For example,the spaceborne atomic clock of BDS-3 is upgraded for higher performance,the Ka-band inter-satellite link is adopted for inter-satellite ranging and communication,and new B1C and B2a signals are broadcast in addition to B1I and B3I signals(compatible with BDS-2).In addition,a 9-parameter model based on a spherical harmonic function is employed for ionospheric delay corrections.Using the observation data from 18 satellites of the basic system,this paper conducts a comprehensive evaluation of the pseudorange measurement characteristics,signal-in-space(SIS)accuracy of navigation messages and global service capability of BDS-3.The results indicate that the pseudorange measurement multipath effect and observation noise of BDS-3 satellites are better than those of BDS-2;additionally,with the support of inter-satellite links,the user range error(URE)of the BDS-3 satellite broadcast ephemeris is better than 10 cm,the precision of the broadcast clock parameter is better than 1.5 ns,and the SIS accuracy is better than 0.6 m overall.Different from the traditional Klobuchar model,the BeiDou global broadcast ionospheric delay correction model(BDGIM)can provide ionospheric delay corrections better than 70%for worldwide single-frequency users.The service capability evaluation of the basic system consists mainly of the accuracy improvement of the B1I and B3I signals according to BDS-2 as well as the global positioning accuracy of the new signals.These results prove that the BDS-3 basic system has achieved the design goal;that is,both the horizontal and the vertical global positioning accuracies are better than 10 m(95%).In the future,6 MEO satellites as well as 3 GEO satellites and 3 IGSO satellites for regional enhancement purposes will be deployed for full operation;consequently,BDS-3 will definitely provide a higher SIS accuracy and better service capability. | JinPing Chen XiaoGong Hu ChengPan Tang ShanShi Zhou YuFei Yang JunYang Pan Hui Ren YueXin Ma QiuNing Tian Bin Wu Yang Yu | 2020 | Science China(Physics,Mechanics & Astronomy)2020，63，6： | 14 |
| 12 | Precise orbit determination of a maneuvered GEO satellite using CAPS ranging data显示文摘Wheel-off-loadings and orbital maneuvers of the GEO satellite result in additional accelerations to the satellite itself. Complex and difficult to model, these time varying accelerations are an important error source of precise orbit determination (POD). In most POD practices, only non-maneuver orbital arcs are treated. However, for some applications such as satellite navigation RDSS services, uninterrupted orbital ephemeris is demanded, requiring the development of POD strategies to be processed both during and after an orbital maneuver. We in this paper study the POD for a maneuvered GEO satellite, using high precision and high sampling rate ranging data obtained with Chinese Area Positioning System (CAPS). The strategy of long arc POD including maneuver arcs is studied by using telemetry data to model the maneuver thrust process. Combining the thrust and other orbital perturbations, a long arc of 6 days’ CAPS ranging data is analyzed. If the telemetry data are not available or contain significant errors, attempts are made to estimate thrusting parameters using CAPS ranging data in the POD as an alternative to properly account for the maneuver. Two strategies achieve reasonably good data fitting level in the tested arc with the maximal position difference being about 20 m. | HUANG Yong HU XiaoGong HUANG Cheng YANG QiangWen JIAO WenHai | 2009 | Science China(Physics,Mechanics & Astronomy)2009，52，3： | 13 |
| 13 | Precise positioning of the Chang'E-3 lunar lander using a kinematic statistical method显示文摘A kinematic statistical method is proposed to determine the position for Chang'E-3(CE-3) lunar lander.This method uses both ranging and VLBI measurements to the lander for a continuous arc,combing with precise knowledge about the motion of the moon as provided by planetary ephemeris,to estimate the lander's position on the lunar surface with high accuracy.Accuracy analyses are carried out with simulation data using the software developed at Shanghai Astronomical Observatory in this study to show that measurement errors will dominate the position accuracy.Application of lunar digital elevation model(DEM) as constraints in the lander positioning is also analyzed.Simulations show that combing range/doppler and VLBI data,single epoch positioning accuracy is at several hundred meters level,but with ten minutes data accumulation positioning accuracy is able to be achieved with several meters.Analysis also shows that the information given by DEM can provide constraints in positioning,when DEM data reduce a 3-dimensional positioning problem to 2-dimensional.Considering the Sinus Iridum,CE-3 lander's planned landing area,has been observed with dedicated details during the CE-1 and CE-2 missions,and its regional DEM model accuracy may be higher than global models,which will certainly support CE-3's lander positioning. | HUANG Yong HU XiaoGong LI PeiJia CAO JianFeng JIANG DongRong ZHENG WeiMin FAN Min | 2012 | Chinese Science Bulletin2012，57，35： | 11 |
| 14 | Orbit determination and prediction for Beidou GEO satellites at the time of the spring/autumn equinox显示文摘Geostationary(GEO) satellites form an indispensable component of the constellation of Beidou navigation system(BDS). The ephemerides, or predicted orbits of these GEO satellites(GEOs), are broadcast to positioning, navigation, and timing users. User equivalent ranging error(UERE) based on broadcast message is better than 1.5 m(root formal errors: RMS) for GEO satellites. However, monitoring of UERE indicates that the orbital prediction precision is significantly degraded when the Sun is close to the Earth's equatorial plane(or near spring or autumn Equinox). Error source analysis shows that the complicated solar radiation pressure on satellite buses and the simple box-wing model maybe the major contributor to the deterioration of orbital precision. With the aid of BDS' two-way frequency and time transfer between the GEOs and Beidou time(BDT, that is maintained at the master control station), we propose a new orbit determination strategy, namely three-step approach of the multi-satellite precise orbit determination(MPOD). Pseudo-range(carrier phase) data are transformed to geometric range(biased geometric range) data without clock offsets; and reasonable empirical acceleration parameters are estimated along with orbital elements to account for the error in solar radiation pressure modeling. Experiments with Beidou data show that using the proposed approach, the GEOs' UERE when near the autumn Equinox of 2012 can be improved to 1.3 m from 2.5 m(RMS), and the probability of user equivalent range error(UERE)<2.0 m can be improved from 50% to above 85%. | LI XiaoJie ZHOU JianHua HU XiaoGong LIU Li GUO Rui ZHOU ShanShi | 2015 | Science China(Physics,Mechanics & Astronomy)2015，58，8： | 8 |
| 15 | Analysis of RDSS positioning accuracy based on RNSS wide area differential technique显示文摘The BeiDou Navigation Satellite System(BDS) provides Radio Navigation Service System(RNSS) as well as Radio Determination Service System(RDSS).RDSS users can obtain positioning by responding the Master Control Center(MCC) inquiries to signal transmitted via GEO satellite transponder.The positioning result can be calculated with elevation constraint by MCC.The primary error sources affecting the RDSS positioning accuracy are the RDSS signal transceiver delay,atmospheric trans-mission delay and GEO satellite position error.During GEO orbit maneuver,poor orbit forecast accuracy significantly impacts RDSS services.A real-time 3-D orbital correction method based on wide-area differential technique is raised to correct the orbital error.Results from the observation shows that the method can successfully improve positioning precision during orbital maneuver,independent from the RDSS reference station.This improvement can reach 50% in maximum.Accurate calibration of the RDSS signal transceiver delay precision and digital elevation map may have a critical role in high precise RDSS positioning services. | XING Nan SU RanRan ZHOU JianHua HU XiaoGong GONG XiuQiang LIU Li HE Feng GUO Rui REN Hui HU GuangMing ZHANG Lei | 2013 | Science China(Physics,Mechanics & Astronomy)2013，56，10： | 6 |
| 16 | Applications of two-way satellite time and frequency transfer in the BeiDou navigation satellite system显示文摘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. | ShanShi Zhou XiaoGong Hu Li Liu Rui Guo LingFeng Zhu ZhiQiao Chang ChengPan Tang XiuQiang Gong Ran Li Yang Yu | 2016 | Science China(Physics,Mechanics & Astronomy)2016，59，10： | 6 |
| 17 | Satellite-station time synchronization information based real-time orbit error monitoring and correction of navigation satellite in Beidou System显示文摘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. | HE Feng ZHOU ShanShi HU XiaoGong ZHOU JianHua LIU Li GUO Rui LI XiaoJie WU Shan | 2014 | Science China(Physics,Mechanics & Astronomy)2014，57，7： | 3 |
| 18 | Solution of regional GPS network using Precise Point Positioning with undifferenced data 显示文摘 | Huang Cheng Hu Xiaogong and Chen Zhongyi | 2002 | Chinese Astronomy and Astrophysics2002，26，1： | 1 |
| 19 | Evaluation of Compass Ionospheric Model in GNSS Positioning 显示文摘 | WU Xiaoli HU Xiaogong WANG Gang | 2012 | Advance in Space Research2012，51，95： | 1 |
| 20 | Signal-in-space accuracy for BeiDou navigation satellite system:Challenges and solutions显示文摘Service accuracy of global navigation satellite system(GNSS)is determined by satellite constellation,signal-in-space(SIS)accuracy and signal transmission errors.The State Council Information Office of the People's Republic of China issued China's BeiDou Navigation Satellite System(BDS)White Paper(www.beidou.gov.cn/fbh2016.html)on Jun.16th 2016,which notes that,BDS takes a three-step development strategy,from domestic service,through Asia-Pacific regional service,to global service,and features mixed constellation of Geostationary Earth Orbit(GEO),Inclined Geostationary Earth Orbit(IGSO)and | ShanShi Zhou Bin Wu XiaoGong Hu YueLing Cao Yang Yu | 2017 | Science China(Physics,Mechanics & Astronomy)2017，60，1： | 0 |
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