GPS Omnidirection Antenna Modem Beamed Development Update Antenna Base Base Station Urban Station Ring Navigation and Positioning in China Urban Ring Line Users Line Jingnan Liu, Chuang Shi, Linyuan Xia, and Hui Liu

FIGURE 1 Shenzhen CORS station established in China Base Station Urban Users Ring at applications for surveying and map- Base Station Urban Line Ring ping, urban planning, resource manage- Line ment, transportation monitoring, disas- ter prevention, and scientific research FM Station Base including meteorology and ionosphere Monitoring Burg

Station scintillation. Positioning Center Enter into der Municipal Urban Signal mobile van In this way, the Shenzhen CORS net- Communication Ring Transmitter system work is acting to energize the booming Center Line economy of this young city. With rapid FIGURE 2 Lay out of CORS network in Shenzhen development of CORS construction in China, these stations are expected to operate within a standard national and SLR and pro- istockphoto.com/Hester GNSS RINEX Single Cleaned GNSS GNSS/LEO Satellite ICs © specification and to play vital roles in duce long baseline data station data data orbit Satellite cleaning SST ranging data integrator description During the past 15 years, China has steadily accelerated its activities in realization of the “digital city” in terms and satellite orbit SLR data Observed attitude of real-time and precise positioning and outputs. PANDA GNSS/LEO orbit Observed the realm of satellite navigation and positioning. Researchers from leading navigation. can perform orbit file acceleration GNSS engineering centers in Wuhan provide an overview of these efforts. Based on CORS stations properly determination for Data cleaning based Estimator Ambiguity on residuals/update • Least Square Adjustment contraints distributed throughout China, some of GPS and low earth initial values for high precision post- these facilities are aligned with stations orbiting (LEO) sat- mission applications Integer • Square Root Information evelopment of satellite-based southern California, USA. This innova- In contrast to preliminary stages, installed with other spatial observing ellites, and its results ambiguity Filter for kinematic or real- resolution positioning and naviga- tion successfully helped geologists to evolution of networks and communi- technologies such as SLR, VLBI and can match those of time applications tion technology has greatly deepen their understanding of seismic cations have enabled CORS to become DORIS (Doppler Orbitography and such agencies as the Post-fit residuals Dreformed conventional spatial faults because more continuous spatial a leading support component for the Radio-positioning Integrated by Satel- International GNSS Free/Fixed solutions determination practices and enabled information can be obtained than ever national temporal and spatial informa- lite, a system maintained by France). Service (IGS), JPL, Products Solution Combination Real-time Products advancement of the digital infrastruc- before. tion infrastructure. CORS is now imple- These sites are serving for satellite orbit Scripps Institution • Site deformation Products Generation • Site pos/vel. and • LEO orbit/trajectory Products Publication clocks ture in China. This kind of progress is From 1997 to 2000, as a key state sci- mented at many of China’s main cities, determination and, when combined with of Oceanography, • GNSS orbits and clocks • Zenith Troposphere continuing with the improvement of entific project, the Crust Motion Obser- such as Shenzhen, Chengdu, Beijing, multiple spatial technologies, have cre- the European Space • Earth rotation Delay parameters • LEO orbit/trajectory related techniques. vation Network of China (CMONOC) Shanghai, and Guangzhou. ated a dynamic and multi-dimensional Agency (ESA), the • Gravity model • GNSS orbits and This article will provide an update was implemented, composed of 25 CORS Among these, the Shenzhen CORS terrestrial reference frame for China. U.S. National Geo- • etc. clocks on China’s GNSS-related activities in stations and 1,000 regional network sta- system was started in 1999 as a paradigm detic Survey, the recent years, including research on novel tions. Very long baseline interferometry of comprehensive service network and PANDA & Orbit Center for Orbit FIGURE 3 Schematic design of PANDA software for satellite orbit determi- nation positioning approaches, collaborations (VLBI) and satellite laser ranging (SLR) spatial data infrastructure in China. (See Determination Determination in between China and international sec- equipment was coupled in some of the Figures 1 and 2.) The system was designed With funding support from relevant Europe (COD), tors, and, finally, some brief comments CORS stations. Based on CMONOC, and implemented in a flexible form of authorities, Wuhan University has Germany’s GeoForschung Zentrum Experiment-A (GRACE-A) satellite with on the prospect for China’s Beidou navi- researchers achieved significant seismic network and wireless communication developed a scientific software called (GFZ), and Canada’s Energy, Mines the satellite elevations computed by SLR gation and positioning system. motion results about continental plates. to perform a variety of positioning and PANDA (for Position and Navigation and Resources (now Natural Resources stations. CORS has subsequently been employed navigation services in both real-time Data Analysis) that comprehensively Canada) facility (EMR). In the software packages, we have China’s CORS Network by numerous agencies and organizations and postprocessing. analyzes multiple spatial observations Figure 4 compares the IGS and considered all possible parameters such Beginning in 1990, the mode of continu- in China and has become popular in The project was jointly accomplished and autonomously determines satellite PANDA orbit determination root mean as earth orientation and right-hand ously operating reference station (CORS) many fields, including guidance of air- by the GNSS Engineering Research Cen- orbits. Figure 3 shows the data process- square (RMS) fits of GPS orbits with the circular (RHC) phase-rotation correc- using GPS was first applied by NASA’s craft similar to the U.S. Wide Area Aug- ter, Wuhan University, and Shenzhen ing scheme of the PANDA software. results from IGS Analysis Centers. Fig- tions, and various force models includ- Jet Propulsion Laboratory (JPL) and mentation System (WAAS) approach Municipal Bureau of Land Resources The software can currently accom- ure 5 compares PANDA range residuals ing gravity model, third-body attraction, MIT to the research of plate tectonics in procedures. and Housing Management. It is aimed modate observations including GPS to the Gravity Recovery And Climate tides, atmospheric drag, solar radiation,

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90 0.100 60 single-frequency GPS receivers. Studies Recently, a study has 50 are focusing on compensation methods gotten under way on the 0.050 ACs ACs 40 for ionospheric delay, phase unwrap- potential use of combina- 60 (2004) 0.000 30 ping, and receiver bias–induced effects, tions of three or multiple which will lead to further refinements of frequencies and their prop-

20 Elevation (o) Residuals (m) -0.050 this positioning approach. erties in light of the Gali- 30 10 SLR residuals Elevation To meet user requirement for accu- leo system. Research is also -0.100 0 rate three-dimensional (3-D) position- being conducted on the Orbit RMS wrt IGS (mm) FIGURE 5 Residuals by PANDA and elevations of satellite laser ranging ing in local datums, research on refined realization and improve-

0 cod em gfz jpl sio es ng g+c (fix g+c (free) gps (fix) gps (free) observations to GRACE-A a s quasi-geoids is now fully performed ment of the Galileo Ter- r in most big cities in China. Tests have restrial Reference Frame ) kinematic applica- tion, GPS attitude control, and gravity shown that refined quasi-geoid results combining observations tions. model recovering. can achieve levels of geoid height results from Galileo, VLBI, SLR, FIGURE 4 Overall PANDA orbit RMS (in millimeters) compared with the Fig- IGS final results. Green is that of PANDA, yellow is for that of the IGS In the future, With precise orbit support and flexi- with centimeter-level accuracy. (See DORIS, and other sources. Analysis Centers (ACs) over the same time, and red for ACs around the signal observations ble services including atmospheric prod- ure 6.) This can further enable position- end of 2004. from Galileo and ucts by IGS and other agencies, single ing and navigation, including 3-D pre- The Beidou System other systems will point positioning is also rapidly push- cise point positioning relative to local China’s third Beidou velocity impulse, and acceleration obser- be included in the software to further ing towards maturity in China using height datums by using GNSS. navigation satellite was vations. Some ambiguous factors can be enrich its orbit determination capability. refined ambiguity resolution algorithms. launched into orbit on May compensated by estimated parameters. Some recently planned research aspects Research results by Wuhan University International Cooperation 25, 2003 (see Figure 7). That Observation equations are generated for this software may cover tropospheric and other departments show that the Apart from research based on current marked the formation of epoch by epoch within an estimator to delay estimation from a moving plat- accuracy for postprocessing is at the satellite navigation systems, interna- a complete local satellite meet the requirement of real-time or form, onboard precise orbit determina- centimeter level using both dual- and tional collaborations on use of other navigation and positioning satellite systems, especially Galileo, system. This system is based form an important aspect of China’s on positioning principle GNSS-related activities. Following using twin satellites first an official agreement between China proposed in 1983. Beidou and the European Union reached in is designed to conduct all- FIGURE 7 Blastoff of the third BD1 on May 25, 2003. October 2003, the Ministry of Science weather navigation, posi- and Technology of China (MOST), tioning, timing, and communication point positioning can also be carried out European Commission (EC) and ESA using short messages by radiobeacons based on this capability. (See Figure 8.) In established the Chinese-Europe GNSS on board the satellites. this way, an augmentation system that is Technology Training and Corporation Beidou is composed of a control sta- similar to WAAS or the European Geo- Center (CENC), which is headquartered tion, orbit network stations, calibration stationary Navigation Overlay Service at MOST. stations, altimetry stations, and a user (EGNOS) can be derived from Beidou A technology cooperation agreement transceiver unit. Currently, the system in the future when an enhanced system on Galileo was signed in October 2004 can provide positioning service with an is completed. in which representatives from related accuracy of about 20 to 100 meters and Considering the approaching appli- ministries, industrial sectors, and uni- a timing service with about 20-nano- cation of Galileo and China’s Beidou versities participated. Several seminars second precision. To improve its perfor- system, research on employment of mul- have been held on China-Europe Gali- mance, one proposal suggests that the tiple frequency signal sources to facilitate leo collaboration and satellite navigation Beidou 1 satellite could act as communi- precise point positioning are also being industry development, aimed at promot- cation link for an augmentation service carried out by interested departments. ing this cooperation. in addition to its positioning function. These research projects are discussing Given this mechanism, Wuhan Uni- Technology schemes completed as the opportunity brought by these sig- versity and the Shanghai Astronomical part of the research for China’s wide nals to overcome atmospheric effects on Observatory (SHAO) in China have col- area differential GNSS project have laid GNSS signal propagation and to enable laborated with the EU to participate in a good foundation for enhanced real raw phase ambiguity resolution for com- the EC’s 6th Framework Program (FP6). time and accurate positioning using bined phase observations. With FP6 support, a technical research the current Beidou system. Because In order to maintain a long-term and data analysis center for the Galileo Beidou’s communication data link is development on the basis of full compat- system in China will be established and self-contained, it can be used as link for ibility with existing and coming satel- a plan will be implemented to develop a broadcast of grid atmospheric delay cor- lite navigation systems, various Chinese FIGURE 6 Quasi-geoid heights in western China, scale in meters with resolution of 1 minute 30 seconds by 1 minute 30 seconds (courtesy of School of prototype of for a Galileo geodesy ser- rections, ephemerides, and other correc- public organizations (including Wuhan Geodesy and Geomatics, Wuhan University, 2005) vice provider. tions. As a result, real-time and precise University) and industrial enterprises

48 InsideGNSS september 2006 www.insidegnss.com www.insidegnss.com september 2006 InsideGNSS 49 development in china

GPS satellites anism of Geodetic nation,” The Fourth International Symposium on Knowledge” project GPS/GNSS, Nov. 6-8, 2002, Wuhan, China, Wuhan BD1 funded by National University Journal of Natural Science, Vol. 8, No. 973 Fundamental 2B, pp 603-609, 2003 Research Planning 6. Li J., and J. Chen, J. Ning, and D. Chao, Earth Gravity Approximation Theory and Determination Monitor in 2005. Station of Quasi-geoid 2000 of China, Wuhan University Users Additional Press, 2003 Users Resources 7. Springer T. A., and G. Beutler and M. Rothacher, Users 1. Altamimi Z., and “Improving the Orbit Estimates of GPS Satellites,” Journal of Geodesy, Vol. 73:147-157, 1999 Base P.Sillard P and C. Bouch- Station Orbit Analysis er, “ITRF2000: A New 8. Zhu S., and C.Reigber and R. Koenig, “Integrat- Center Release of the Interna- ed adjustment of CHAMP, GRACE, and GPS data,” Regional Differential tional Terrestrial Ref- Journal of Geodesy, 78:103-108, 2004. Service Center Base erence Frame for Earth Station 9. Zumberge J. F., and M. B. Heflin, D. C. Jeffer- Science Applications,” son, M. M. Watkins, and F. H. Webb, “Precise Point Journal of Geophysical Positioning for the Efficient and Robust Analysis FIGURE 8 Augmentation scheme based on Beidou satellites Research, 2002 of GPS Data from Large Networks, Journal of Geod- 2. Dong D. and Y. Bock, “Global Positioning System esy, Vol. 102, No. B3, pp. 5005-5017, 1997 are undertaking initial research on Network Analysis With Phase Ambiguity Resolu- compatible receiver development that tion Applied to Crustal Deformation Studies in Authors can accommodate signals from GPS, California,” Journal of Geophysical Research, Vol. Jingnan Liu is president GLONASS, Galileo, and Beidou. These 94, No. B4, pp. 3949-3966, 1989 studies will lead to convenient use of an and professor of Wuhan 3. Ge M., and E. Calais and J. Haase, “Reducing University, and director integrated satellite navigation system Satellite Orbit Error Effects in Near Real-Time GPS of the university’s GNSS for users in China. Zenith Tropospheric Delay Estimation for Meteo- Engineering Research rology,” Geophysical Research Letters, Vol. 27, No. Center. He graduated Acknowledgements 13, 2000 from the geodesy This report is supported by the sub- 4. Liu J., “Study on Feasibility of Shenzhen CORS department of Wuhan Technical University of Sur- project, “Spatial & Temporal Datum Project,” GNSS Engineering Research Center, veying and Mapping and received his master’s for Earth Observing and Precise Posi- Wuhan University, November 1999 degree in geodesy from the same university. Prof. Liu was elected to the Chinese Academy of Engi- tioning,” of the “Earth Observing Data- 5. Liu J. and M. Ge, “PANDA Software and Its Pre- neering in 1999. His teaching and research has Spatial Information-Transform Mech- liminary Result for Positioning and Orbit Determi- focused on GNSS theory and application, and geo- dynamics. Prof. Liu has led development of sev- eral GNSS software packages for data processing and engineering applications that resulted in sci- entific awards at state levels. Chuang Shi graduated from the geodesy depart- USE IT OR LOSE IT! ment of Wuhan Technical University of Surveying and Mapping. He received his Ph.D. from Wuhan You are at risk of University and is now professor and deputy direc- tor of the GNSS Engineering Research Center, missing out on future Wuhan University. issues of Inside GNSS Linyuan Xia graduated from the geodesy depart- ment of Wuhan Technical University of Surveying unless you register for a and Mapping. He received his Ph.D. from Wuhan FREE subscription at University and is now a professor at the State Key Laboratory for Information Engineering on www.insidegnss.com Surveying, Mapping and Remote Sensing (LIES- MARS), Wuhan University. Hui Liu graduated from the Geodesy Depart- ment, Wuhan Technical University of Surveying and Mapping. He received his Ph.D. from Wuhan University and is now associate professor at the GNSS Engineering Research Center, Wuhan Uni- versity.

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