IGS-MGEX Preparing the Ground for Multi-Constellation GNSS Science
OLIVER MONTENBRUCK With four new and emerging constellations (BeiDou, Galileo, GERMAN AEROSPACE CENTER (DLR), GERMAN SPACE OPERATIONS CENTER (GSOC) QZSS, IRNSS) as well as the ongoing modernization of the PETER STEIGENBERGER U.S. Global Positioning System and Russia’s GLONASS, INSTITUTE FOR ASTRONOMICAL AND PHYSICAL the world of satellite navigation is undergoing dramatic GEODESY, TECHNISCHE UNIVERSITÄT MÜNCHEN ROBERT KHACHIKYAN changes. Facing these challenges, the International GNSS NASA JET PROPULSION LABORATORY/ Service has initiated the Multi-GNSS Experiment to enable INTERNATIONAL GNSS SERVICE CENTRAL BUREAU an early familiarization with the new systems and to prepare GEORG WEBER GERMAN FEDERAL AGENCY FOR CARTOGRAPHY their incorporation into high-precision GNSS modeling AND GEODESY and analysis. This article reports on the status of the new RICHARD B. LANGLEY constellations and the MGEX project and describes initial UNIVERSITY OF NEW BRUNSWICK, GEODESY AND GEOMATICS ENGINEERING data products and recent results for individual systems. LEOŠ MERVART TECHNICAL UNIVERSITY OF PRAGUE, FACULTY OF CIVIL ENGINEERING ver the past decade, the world These independent services are further URS HUGENTOBLER of global positioning has expe- complemented by a variety of satellite- INSTITUTE FOR ASTRONOMICAL AND PHYSICAL rienced dramatic changes. based augmentation systems (SBASs) GEODESY, TECHNISCHE UNIVERSITÄT MÜNCHEN O Starting from just a single con- to increase the availability, accuracy, stellation (GPS), a set of six global or and reliability of PNT for safety-critical regional navigation satellite systems — applications. with the addition of GLONASS, BeiDou, The potential merits of the new navi- GNSS monitoring station at the German Galileo, Quasi-Zenith Satellite System gation satellite systems have long been Antarctic Receiving Station (O’Higgins), (QZSS) and the Indian Regional Navi- praised and often been used to justify jointly operated by the Federal Agency for gation Satellite Systems (IRNSS) — has the need for their build-up. Leaving Cartography and Geodesy (BKG) and the emerged that are already offering, or at aside the political arguments for an German Aerospace Center (DLR) least preparing, a space-based position, independent national PNT infrastruc- navigation, and timing (PNT) service. ture, multi-constellation systems can
42 InsideGNSS JANUARY/FEBRUARY 2014 www.insidegnss.com indeed offer numerous advantages over ing Group. MGEX serves as a framework System Blocks Signals Sats stand-alone GPS navigation and the use for increasing the overall awareness of L1 C/A, L1/L2 IIA 8 of its legacy ranging signals. New signal multi-GNSS within the scientific and P(Y) structures will not only provide a greater engineering communities, as well as to L1 C/A, L1/L2 IIR-A/B 12 robustness against interference and mul- familiarize IGS participants and users GPS P(Y) tipath but also enable more robust track- with the new navigation satellite sys- IIR-M +L2C 7 ing at low signal levels. tems. The availability of unencrypted sig- This article will provide a brief over- IIF +L5 4 nals on three frequencies enables new view of new and modernized GNSS con- M L1/L2 C/A + P 24 GLONASS approaches to ambiguity resolution in stellations and their transmitted signals K +L3 (1) carrier-phase–based relative positioning as available in fall 2013. Thereafter, it GEO B1, B2, B3 5 and may also contribute to the analysis describes the MGEX network, which BeiDou IGSO B1, B2, B3 5 of higher-order ionospheric path delays. the IGS has established for multi-GNSS Last, but not least, the simple increase tracking and is operated in parallel to MEO B1, B2, B3 4 E1, (E6), in the number of available satellites not the legacy network in use for GPS and Galileo IOV (4) only enhances navigation applications, GLONASS. E5a/b/ab but also offer an increased number of A subsequent section presents ini- L1 C/A, L1C, signals for space weather applications tial MGEX data products, assesses their QZSS n/a SAIF 1 L2C, E6 LEX, L5 that employ occultation techniques and achieved performance, and discusses ray tracing of the neutral atmosphere relevant processing standards. We con- IRNSS n/a L5,S (1) and the ionosphere. clude with a discussion of necessary TABLE 1. Deployment status of global and regional Given the remarkable contributions steps and actions required in order to navigation satellite systems as of September to science that GPS continues to make fully incorporate new constellations and 2013. Satellites marked in brackets have not been declared operational. in geodesy, remote sensing, space, and signals into the IGS service portfolio. fundamental physics, similar and even larger benefits are commonly expected Navigation Satellite than the legacy signals. Upon full imple- from the new space-based PNT systems. Systems Status mentation in December 2014, CNAV Many of the cited applications make Table 1 summarizes current space-based signal accuracy should meet or exceed direct or indirect use of the Interna- PNT systems and operational satel- the legacy signals. tional GNSS Service (IGS), which has, lites as derived from the publication In addition to GPS and GLONASS, over many years, set the gold standard by R. Langley cited in the Additional the BeiDou system now offers a stand- for high-precision GPS and GLONASS Resources section near the end of this alone navigation service for the China measurement modeling and analysis. article. With the most recent launch of mainland and Asia-Pacific area, with a The IGS is a volunteer organization IRNSS-1A, a total of six navigation sat- global service expected to be available of more than 200 individual agencies ellite systems have so far become avail- by about 2020. Even though the BeiDou and institutions that maintain a global able. Among these, the legacy systems Open Service Interface Control Docu- network of monitoring stations and a GPS and GLONASS have long achieved ment (ICD) only covers the B1 and B2 long-term tracking data archive as well their full operational capability and pro- Open Service signals at present, signals as products derived from the analysis of vide navigation signals on at least two on up to three BeiDou frequencies can these measurements. frequencies (L1, L2) that can be accessed in fact be tracked by a variety of multi- With the advent of modernized GPS by civil users. GNSS receivers. BeiDou is thus the signals and the rise of numerous new The latest generations of GPS IIF first constellation enabling a systematic GNSS such as BeiDou, Galileo, QZSS, and GLONASS-K satellites have added assessment of triple-frequency position- and IRNSS as well as new augmenta- a third frequency (L5 and L3, respec- ing techniques. tion systems such as Russia’s System tively), but these signals remain limited Galileo presently has four in-orbit of Differential Correction and Moni- to a very small number of spacecraft. In validation (IOV) satellites in operation. toring (SCDM) and India’s GPS Aided June 2013, the GPS Directorate started These satellites support early testing and GEO Augmented Navigation (GAGAN) an initial test campaign with live broad- experimentation but have not yet been system, the IGS is fully committed to casts of the new L2C and L5 CNAV navi- declared healthy. An initial operational expand to a true multi-GNSS service. gation messages. These offer enhanced service with global coverage is targeted To pave the way for future provision navigation information and improved for a few years from now. Although of high-quality data and products for all positioning capabilities. The message- access to the Galileo E6 signals is still constellations, the IGS has initiated the populated broadcast is projected to not fully defined, users can freely access Multi-GNSS Experiment (MGEX) under begin April 2014. Users should expect signals with advanced multi-path per- coordination of its Multi-GNSS Work- initial CNAV signal accuracy to be less formance in the E1 and E5a/E5b bands. www.insidegnss.com JANUARY/FEBRUARY 2014 InsideGNSS 43 IGS-MGEX
As a unique feature, the Galileo satel- stations has been lites are equipped with passive hydrogen deployed around masers. These offer exceptional clock the globe in paral- stability with many potential benefits lel to the legacy IGS for real-time navigation, precise posi- network for GPS tioning, and science applications. a nd GLONASS. Japan has validated the concept of Building on con- QZSS with its “Michibiki” satellite for tributions from more than two years. A fully operational various national QZSS comprising at least three satellites agencies, universi- in inclined geosynchronous orbit (IGSO) ties, and other vol- FIGURE 1 MGEX station distribution and supported constellations (as of and one in geostationary orbit (GEO), is unteer institutions, September 2013) envisaged within the present decade. the MGEX network QZSS supports a unique portfolio of had grown to almost 90 stations by Sep- cant challenge for consistent data pro- navigation signals on four distinct fre- tember 2013 (See Figure 1). cessing, this variety is, at the same time, quency bands and offers various types MGEX largely draws on the resourc- a valuable asset. The diversity of avail- of correction data for medium and high- es of institutions that have modernized able tracking techniques and types of accuracy users. their legacy GNSS monitoring net- data employed by the various receivers Finally, India launched a first satel- works in recent years or established contributes to a thorough understanding lite, IRNSS-1A, in July 2013, which is new multi-GNSS–capable monitoring and assessment of new navigation sig- currently undergoing testing. Four IGSO stations. Overall, about two-thirds of nals. Also, the cross-comparison of dif- and two GEO satellites will ultimately all MGEX stations are contributed by ferent types of equipment contributes to comprise IRNSS. IRNSS-1A is transmit- France’s Centre National d’Etudes Spa- continued evolution and improvement ting signals in both the L5 and S bands, tiales (CNES) and the Deutsches Geo- of GNSS receiver design by the manu- but common GNSS receivers cannot ForschungsZentrum (GFZ) as well as facturers. presently track these signals due to the the Deutsches Zentrum für Luft- und Six MGEX sites presently host multi- lack of information about the L5 ranging Raumfahrt (DLR), the European Space ple receivers of different types connected codes employed and the unique choice Agency (ESA), and the Bundesamt für to a common antenna (Table 2 in Manu- of the second signal frequency. It is also Kartographie und Geodäsie (BKG). The facturers section). This enables a direct presently unclear whether addition of an MGEX website provides an up-to-date comparison of the tracking behavior and L1 signal is being considered for upcom- map and list of all MGEX stations along assists the assessment of receiver-specific ing IRNSS satellites to improve interop- with links to station-specific sitelog files. differential code and carrier phase biases erability with existing systems. As a minimum, all MGEX stations for individual GNSS signals. The six navigation satellite systems support tracking of GPS as well as one Data centers at the NASA Crustal that we have described here are comple- of the new BeiDou, Galileo, or QZSS Dynamics Data Information Sys- mented by a total of 13 SBAS satellites constellations. While not a prerequisite, tem (CDDIS), the French Institut in geostationary orbit. While not in the GLONASS is likewise supported by the Géographique National (IGN), and BKG immediate focus of the IGS and the sci- majority of stations and a large frac- archive and distribute the observation entific community, a growing number tion also offers L1 or L1/L5 SBAS track- data and broadcast ephemerides collect- of SBAS satellites already offer dual-fre- ing. However, no stations with IRNSS ed by the MGEX network. To facilitate quency (L1/L5) ranging signals that can tracking capability have, so far, become these activities, the Receiver Indepen- be tracked by modern GNSS receivers available for the MGEX project due to dent Exchange Format (RINEX 3) has and may become of interest for future the lacking signal specification and the consistently been adopted throughout precise positioning applications. very early project status. the MGEX project. Implementation of An up-to-date overview of the GNSS MGEX builds on a highly hetero- the latest version 3.02 is in progress, but system status with focus on new constel- geneous network comprising a wide legacy DOS-style (8+3) filenames are lations is maintained at the website of the range of end user equipment. The most currently retained for compatibility with IGS Multi-GNSS project (listed in Addi- widely used receiver types are listed in existing processing infrastructure. tional Resources) along with supporting the Manufacturers section near the end Introduction of new filenames with information for the data processing. of this article. Most sites employ choke extended information fields as fore- ring antennas but survey-grade anten- seen in the new RINEX 3.02 standard The IGS Multi-GNSS nas with conventional ground-planes is planned at a later stage in coordina- Network are likewise employed at many stations. tion with MGEX users and the IGS As a backbone of the MGEX project, a Even though the variety of employed Infrastructure Committee. As a mini- new network of multi-GNSS monitoring receivers and antennas poses a signifi- mum, daily RINEX observation files
44 InsideGNSS JANUARY/FEBRUARY 2014 www.insidegnss.com pute precise orbit and clock products for Galileo and QZSS based on observations of the MGEX network and, optionally, other proprietary stations. The data are publicly available for interested users at the MGEX product archive maintained by the CDDIS. Similar efforts are expected in the near future for BeiDou. Galileo. Technische Universität München (TUM) and CNES/Collecte Localisation Satellites (CLS) routinely provide orbit and clock products for the four Galileo IOV satellites (PRN E11, E12, E19, and E20) with latencies of three to six days. These are complemented by various batches of reprocessed FIGURE 2 MGEX real-time network (as of September 2013) ephemeris contributed by the Center for Orbit Determination in Europe (CODE) and GFZ. Overall, as shown in Figure 3, the CODE MGEX orbit and clock products of Galileo presently cover a GFZ time span of almost 1.5 years, which enables long-term perfor- CNES CLS mance assessments under a wide range of conditions. In the absence of published values for the GNSS antenna TUM offset from the center-of-mass, conventional values of x,( y, z) = 1670 1680 1690 1700 1710 1720 1730 1740 1750 (+0.2, 0.0, +0.6)m have been adopted for the MGEX project and GPS Week are recommended for the observation modeling when working FIGURE 3 Availability of Galileo precise orbit and clock products in mid with the MGEX orbit and clock products. These values refer Sep. 2013 to the orientation of the Galileo spacecraft coordinate system illustrated in Figure 4. at a 30-second sampling rate are provided for all stations, but Similar to GPS, the IOV satellites employ a yaw-steering hourly and/or 15-minute high-rate observations files are like- about the Earth-pointing z-axis to maintain the solar panel wise offered for selected sites through the individual data cen- axis y perpendicular to the Sun-direction. Other than for GPS, ters. Links to the MGEX data archives can again be found at however, the Sun is always maintained in the ‒x hemisphere, the MGEX website. while the +x-panel carrying the atomic frequency standard is In addition to offline data, a large subset of stations also pro- oriented towards the deep space. The article by A. Konrad et vides real-time data streams with multi-GNSS observations to alia listed in Additional Resources discusses this subject in the MGEX project (Figure 2). BKG, Frankfurt, hosts a dedicated greater detail. online caster
Precise Orbit and Clock Products FIGURE 4 Orientation of the Galileo-IOV spacecraft coordinate system and location of the GNSS antenna and the laser retroreflector(artist’s As a first step towards the incorporation of new constellations drawing, ESA) into an IGS multi-GNSS service, various analysis centers com- www.insidegnss.com JANUARY/FEBRUARY 2014 InsideGNSS 45 IGS-MGEX
of the SLR measurements with respect to the GNSS- based orbit solutions pro- vide a direct measure of the line-of-sight orbit errors. Figure 6 illustrates the results of this SLR data collection for satellite pairs IOV-1/2 (PRN E11/ E12) and IOV-3/4 (E19/ E20), which are located in orbital planes B and C, respectively. Aside from a mean radial bias of about 5 centimeters, which is as yet unexplained, the residuals show a distinct bow-tie pattern with peak ampli- tudes of about 20 centime- ters and a standard devia- tion of about 8 centimeters.
FIGURE 5 Difference (TUM-minus-CODE) of MGEX precise orbit products for the Galileo IOV These values clearly exceed the self-consistency of the CODE and TUM orbit products and indicate the presence of highly cor- related common errors in both solutions. As may be recognized from a comparison of SLR residuals for individual sat- ellites, the error amplitude is primarily related to the Sun angle above the orbit- al plane (i.e., the β-angle). The residuals are smallest whenever the Sun achieves its maximum elevation
FIGURE 6 Satellite laser ranging residuals of CODE and TUM orbit products for the first (top) and second (bottom) pair of above the respective plane. Galileo IOV satellites. Solid lines indicate the sun angle above the orbital plane (β-angle). However, a secondary minimum can be noted in priate group delay parameters need to CLS orbit products currently show a the vicinity of the eclipse season, when be considered. These can, for example, roughly three times larger error, which the β-angle vanishes. be obtained from the Galileo broadcast can largely be attributed to the use of The radial orbit errors evidenced by ephemeris message. one-day data arcs (as opposed to three- the SLR residuals indicate a subtle error Figure 5 provides a comparison of or five-day solutions provided by the in the modeled accelerations. In view of Galileo IOV precise orbit estimates other analysis centers). their obvious correlation with the Sun from TUM and CODE. Averaging all For an independent performance aspect angle, a deficiency of the solar satellites over the eight-month analysis assessment, we have used satellite laser radiation pressure modeling presently period, the two products exhibit a con- ranging (SLR) measurements collected appears as the most plausible cause of sistency of about 16 centimeters (3D rms by the International Laser Ranging Ser- these errors. Indeed both CODE and position difference). This contributes an vice (ILRS). On average, some 50 normal TUM employ the same 5-parameter orbit-only uncertainty of roughly 5 cen- points are collected per day for each of ECOM model described in the article timeters to the user range error. CNES/ the four Galileo IOV satellites. Residuals by T. A. Springer et alia (Additional
46 InsideGNSS JANUARY/FEBRUARY 2014 www.insidegnss.com analysis center (TUM) determines pre- ing use of proprietary networks as well cise QZSS orbit and clock data based as MGEX monitoring stations. on observations of the MGEX network. For BeiDou satellites in medium However, final QZSS products generated Earth orbit (MEO) and inclined geosyn- by the JAXA control segment based on chronous orbit (IGSO), overlap accura- a mission specific monitoring network cies at the 10-centimeter level (3D posi- have been provided as a complement to tion) and SLR residuals of similar order the TUM products since August of this have been reported in the paper by year. The contribution of a new multi- Q. Zhao et alia (Additional Resources). GNSS ephemeris product generated by BeiDou GEOs achieve a degraded per- FIGURE 7 Clock offsets of the Galileo IOV satellites from GPS Time as derived by MGEX JAXA with the new MADOCA software formance with along-track errors of analysis centers is foreseen in 2014 following dedicated about 0.5 meter as a result of the static inter-agency comparisons and comple- observation geometry. Resources), which is well proven for tion of the software validation. Within the MGEX project, the gen- GPS but appears to be less adequate for Figure 8 compares TUM and JAXA eration of precise orbit and clock prod- the Galileo satellites. Further analyses orbits solutions for QZSS for a one- ucts for BeiDou has not yet started, but will be required to assess the potential month period in July/August 2013. The efforts are made to provide first such benefits of a full-featured box-wing two products exhibit a consistency of products in early 2014. model or a ROCK-type a priori model about 0.7 meter (3D position differ- as proposed in the presentation by D. ence), while the radial component agrees Broadcast Ephemerides Svehla et alia. to roughly 0.1 meter. This is essentially In an effort to provide users with orbit An overview of the Galileo IOV consistent with satellite laser ranging and clock information for all GNSS sat- clock offset and drift based on MGEX residuals of about 0.15 meter for each ellites presently tracked by the MGEX precise ephemeris products is shown in of the two products in the same time network, TUM and DLR generate a Figure 7. Over the past year, the clock off- period. cumulative broadcast ephemeris file sets have mainly been confined to less Although this comparison demon- with GPS, GLONASS, Galileo, BeiDou, than 1.5 milliseconds with typical drifts strates a good performance of MGEX and SBAS information on a daily basis of 5–20 microseconds per day relative to QZSS products during phases of high for the MGEX project. Overall, the file the GPS time scale. β-angle, a degraded quality may appear provides ephemerides of more than 80 Both hydrogen masers and rubidium when QZSS attains an orbit-normal atti- satellites, and this number will increase clocks have been operated in an alter- tude for |β|<20 degrees. Here, the stan- as more satellites are deployed. nating manner on the individual IOV dard IGS yaw-steering attitude model For improved compatibility with satellites. MGEX observations and clock no longer applies, and the parameter- existing software packages, which may products can be used to characterize ization of the radiation pressure must not have full-featured implementation of the Allan deviation over a wide range be adapted to account for the actual ori- the broadcast orbit models for all con- of timescales; however a detailed clock entation of the spacecraft body and the stellations, the IGS will also provide an analysis is beyond the scope of this paper solar panels. SP3 (National Geodetic Survey Standard and left to other publications, e.g., the BeiDou. The BeiDou system declared GPS Format) version of the ephemeris article by A. Hauschild et alia. an operational regional navigation ser- file. In this context, an extension for the QZSS. Next to Galileo, QZSS is the vice in December 2012 and provides SP3c format accommodating more than second emerging navigation satellite sys- broadcast ephemerides of good accuracy 85 satellites has been initiated and is tem for which precise ephemeris prod- to its users. Various Chinese institutions under review within the IGS. ucts are generated within the MGEX (such as Wuhan university) compute Even though the accuracy of the project. As of fall 2013, only one MGEX precise orbit and clock products mak- broadcast orbit and clock information is
FIGURE 8 Difference of TUM and JAXA solutions for QZSS orbit over a one-month period in mid-2013 www.insidegnss.com JANUARY/FEBRUARY 2014 InsideGNSS 47 IGS-MGEX
not fully competitive with precise data sages broadcast with the new L2C, L5, tine application for monitoring of products, the broadcast ephemerides and L1C signals. Nevertheless an effort the overall network. are well suited for numerous applica- was made within the MGEX project to These tasks will help to pave the way tions, such as visibility analysis, quality collect CNAV broadcast ephemerides for a comprehensive consideration of control of observation data, or relative during the first GPS CNAV test trans- new navigation satellite systems in engi- navigation. In case of BeiDou, for which mission in June 2013 with a limited neering and science and strengthen the precise ephemerides are not yet available set of receivers. Aside from binary raw role of IGS as a leading provider of free within the MGEX project, the broadcast navigation data frames transmitted by GNSS data and products of the highest ephemerides achieve a typical user range the Block IIR-M and IIF satellites during quality. error at the 1.5-meter level. The broad- the campaign, the decoded navigation cast ephemerides also provide access and auxiliary data have been archived Summary and Conclusions to timing and broadcast group delay in a RINEX-style format and are made Over the past one to two years a global parameters (TGD, BGD) and inter-con- available to interested users through the multi-GNSS network has been estab- stellation system time offsets for new CDDIS. lished with initial products being deliv- constellations for which no alternative ered to the scientific community. Future products are currently available in the Future Work work within the MGEX project focuses MGEX project. The build-up of the MGEX network has on the incorporation of additional con- In view of the current limitation of laid the foundation for an early famil- stellations, the improved characteriza- the RINEX 3.02 navigation message for- iarization with new GNSS signals and tion of the space and ground segment, mat, the cumulative broadcast file is lim- systems. Even though first steps have and the provision of new product types. ited to legacy (L1 C/A-code) navigation been made to provide precise ephemeris Subject to active participation by MGEX messages for GPS and QZSS, but does products for individual constellations, a analysis centers and a timely build-up not support CNAV and CNAV2 mes- major effort still needs to be made before of the necessary processing chains, the a comprehensive multi-GNSS service MGEX project is expected to transition Site Station Receiver can be offered within the IGS. into a multi-GNSS Pilot Project within Key activities to be pursued by the the next couple of years. CONX Javad TRE_G3TH Delta Concepcion Multi-GNSS Working Group in coop- CONZ Leica GRX1200+GNSS eration with other IGS entities over the Acknowledgment SIN0 Javad TRE_G3TH Delta Singapore next year include: This article is based on a paper presented SIN1 Trimble NETR9 • the expansion of multi-GNSS track- at the 4th International Colloquium on University of UNBD Javad TRE_G2T Delta ing capabilities within the frame of Scientific and Fundamental Aspects New Brunswick UNBS SeptentrioPolaRxS an overall IGS network of the Galileo System held in Prague, • the consideration of additional con- Czech Republic, December 4–6, 2013. University of UNX2 Javad TRE_G3TH Delta stellations (BeiDou, IRNSS and, New South UNX3 Septentrio AsteRx3 Wales optionally SBAS) in the precise Manufacturers ephemeris generation The most used GNSS receiver types in USN4 Septentrio PolaRxTR4 U.S. Naval • the development of a new multi- the MGEX network include the NetR9 Observatory USN5 NovAtel OEM6 GNSS/multi-signal differential code from Trimble, Sunnyvale, California, WTZ2 Leica GRX1200+GNSS bias product and its generation with- USA; Delta-G3TH from Javad GNSS, Wettzell WTZ3 Javad TRE_G3TH Delta in the ionospheric data processing Moscow, Russia, and San Jose, Califor- TABLE 2. Colocated MGEX stations with common • the characterization of the new nia, USA; GR10/25 from Leica Geosys- antennas GNSS satellites (antenna offsets and tems AG, Heerbrugg, Switzerland; and phase pattern, attitude modes, solar PolaRx4 receivers from Septentrio Sat- radiation pressure ellite Navigation nv, Leuven, Belgium. models, maneuvers) MGEX stations make use of choke ring and the development antennas including the Leica AR25R3/4, of common processing Trimble 59800, and Javad Ringant G3T, standards for orbit and as well as survey-grade antennas with clock products conventional ground planes such as the • the development of Trimble Zephyr GII. multi-GNSS/multi- signal quality control Additional Resources tools (noise, multipa- 1. Boriskin, A., and D. Kozlov, and G. Zyryanov, Commonly employed antennas (top) and receivers (bottom) th, cycle slips, and so (2012),“The RTCM Multiple Signal Messages: A within the MGEX network forth), and their rou- New Step in GNSS Data Standardization,” Proceed-
48 InsideGNSS JANUARY/FEBRUARY 2014 www.insidegnss.com ings of the 25th International Technical Meeting 15. Radio Technical Commission for Maritime years with the role of the network coordinator. He of The Satellite Division of the Institute of Navi- Services,RTCM Standard 10403.2 Differential currently maintains and operates the IGS web por- gation (ION GNSS 2012), Nashville, Tennessee GNSS (Global Navigation Satellite Systems) tal at
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