Galileo and BeiDou observation data are now included with Trimble VRS Now subscriptions in North America.
Photo: Trimble
The addition of the Galileo and BeiDou constellations allow users to make use of more satellites, enabling more robust performance when working in harsh GNSS environments such as in urban canyons and under canopy, the company said.
Trimble VRS Now in North America fully supports GPS, GLONASS, QZSS and now, Galileo and BeiDou satellite systems.
The service is powered by the Trimble Pivot Platform GNSS real-time network software, Trimble said. As a true five-constellation solution, it delivers improved real-time positioning performance for customers in North America.
VRS Now is designed for surveying, mapping and GIS, construction and agriculture professionals who require high-accuracy positioning in their workflows.
Adding Galileo and BeiDou observation data provides significant benefits by enabling users to:
Operate in environments where traditional GPS + GLONASS systems’ performances are limited
Improve accuracy and reliability of GNSS solutions
Minimize the effects of multipath and interference
“By including Galileo and BeiDou data, customers can achieve greater accuracy and positioning performance than ever before,” said Patricia Boothe, vice president of Trimble’s Advanced Positioning Division.
With the addition of North America, Trimble VRS Now networks worldwide now support all five GNSS constellations. Besides North America, coverage is available throughout Europe, Australia and New Zealand when using a compatible GNSS receiver or display.
Subscriptions are available through Trimble’s Authorized Business Partners or Trimble’s online store at tpsstore.trimble.com.
VRS Now provides positioning professionals with instant access to real-time kinematic (RTK) and post-processing (PP) corrections using a network of permanent (fixed) continuously operating reference stations (CORS). Professional management and monitoring 24/7 by a global operations team provides peak performance and high reliability, Trimble said.
The U.S. Air Force has awarded Lockheed Martin a $7.2 billion contract to build 22 more GPS III satellites.
Like the first batch of 10 GPS III satellites, the GPS III Follow-On (GPS IIIF) satellites “will provide greater accuracy, and improved anti-jamming capabilities, making them more resilient,” said Air Force Secretary Heather Wilson in a statement.
The satellites will be built at the company’s Waterton campus in the Denver suburb of Littleton.
Under a previous contract, Lockheed is in the process of building 10 GPS III satellites, the first of which is slated to launch in December. The first GPS IIIF satellite could be ready for launch in 2026.
GPS III SV01 on Aug. 20 boards a U.S. Air Force C-17 for its flight to Cape Canaveral, Florida. (Photo: Lockheed Martin)
“We’re grateful for the U.S. Air Force’s continued confidence in Lockheed Martin on the GPS III/IIIF program,” said Johnathon Caldwell, Lockheed Martin’s program manager for Navigation Systems. “We’ve worked hard to develop and produce GPS III to help the Air Force modernize the GPS constellation with new, more powerful, and more resilient, technology.
“This new contract for GPS IIIF will bring GPS to a whole new level. It takes full advantage of our flexible satellite design to incorporate additional new technology like a 100% digital navigation payload, Regional Military Protection and new search-and-rescue payloads into the constellation. We are proud to be bringing these new capabilities to our warfighters and the world.”
Both Boeing and Northrop Grumman declined to bid on the contract, leaving Lockheed Martin the lone provider.
Galileo, BeiDou, QZSS, IRNSS, and more join GPS and GLONASS to bring you wider, broader, greater, more accessible and above all more accurate PNT. How to get all that’s coming at you?
Multi-GNSS paves the way for complete exploitation of new signals and constellations in navigation, surveying, geodesy and remote sensing.
The free 1-hour webinar, which will take place at 1 p.m. Eastern [10 a.m. Pacific, 7 p.m. (1900h) Central European Time] on Thursday, Sept. 20, will review advantages of using multi-GNSS for the end-user and challenges in obtaining maximum efficiency when combining multiple constellations and signals. It will also discuss different approaches of testing GNSS receivers against jamming and spoofing attacks.
You will learn:
Advantages of using multi-GNSS
Challenges when combining multiple constellations
Robustness of multi-GNSS receivers to jamming and spoofing
Test solutions for GNSS receivers.
The webinar presents sponsored content by Skydel and Talen-X. Register for it here.
Once the next-generation GPS III satellites begin launching in December, a series of updates to the current ground control system from Lockheed Martin will help the U.S. Air Force gain early command and control of the new satellites for testing and operations.
In 2016 and 2017, the Air Force placed Lockheed Martin under two contracts, called GPS III Contingency Operations (COps) and M-code Early Use (MCEU), which directed the company to upgrade the existing Architecture Evolution Plan (AEP) Operational Control System (OCS), which operates today’s GPS constellation.
The fourth Lockheed Martin-built GPS Ill satellite is fully integrated. (Photo: Lockheed Martin)
These upgrades to the AEP OCS are intended to serve as gap fillers prior to the entire GPS constellation’s operational transition to the next-generation Operational Control System (OCX) Block 1, now in development.
In April, the Air Force approved Lockheed Martin’s critical design for MCEU, essentially providing a green light for the company to proceed with software development and systems engineering to deploy the M-code upgrade to the legacy AEP OCS.
The Air Force gave a similar nod to COps in November 2016. COps is now on schedule for delivery in May 2019 and MCEU is scheduled for delivery in January 2020.
“The Air Force declared the first GPS III satellite Available for Launch last year, and it’s expected to launch later this year. Nine more GPS III satellites are following close behind in production flow,” explained Johnathon Caldwell, Lockheed Martin’s program manager for Navigation Systems. “GPS III is coming soon, and as these satellites are launched, COps and MCEU will allow the Air Force the opportunity to integrate these satellites into the constellation and to start testing some of GPS III’s advanced capabilities even earlier.”
MCEU Capabilities
Part of the Air Force’s overall modernization plan for the GPS, M-code is a new, advanced signal designed to improve anti-jamming and anti-spoofing, as well as to increase secure access to military GPS signals for U.S. and allied armed forces.
To accelerate M-code’s deployment to support testing and fielding of modernized user equipment in support of the warfighter, MCEU will upgrade the AEP OCS, allowing it to task, upload and monitor M-code within the GPS constellation.
MCEU will provide command and control of M-Code capability to eight GPS IIR-M and 12 GPS IIF satellites currently on orbit, as well as future GPS III satellites.
COps Capabilities
Following launch and check out, each future GPS III satellite will take its place in the GPS constellation. The COps modifications will allow the AEP OCS to support these more powerful GPS III satellites, enabling them to perform their positioning, navigation and timing missions for more than one billion civil, commercial and military users who depend on GPS every day.
Besides the addition of GPS III, COps will also continue to support all the GPS IIR, IIR-M and IIF satellites in the legacy constellation.
Lockheed Martin has a long history of supporting ground systems, providing operations, sustainment and logistics support for nearly 60 Department of Defense satellites, including GPS, often allowing them to double their on-orbit operational design life.
GPS III Satellites
Lockheed Martin also is under contract to develop and build 10 GPS III satellites, which will deliver three times better accuracy and provide up to eight times improved anti-jamming capabilities compared to current GPS satellites.
GPS III’s new L1C civil signal also will make it the first GPS satellite to be interoperable with other international global navigation satellite systems.
With Europe’s Galileo constellation in space now expanded to 26 navigation satellites — and Galileo Initial Services available to users worldwide — the infrastructure on the ground that controls them is undergoing a corresponding expansion.
ESA has awarded a new work order for the Galileo Control Segment — that part of the Galileo system responsible for the monitoring and control of all the satellites in orbit — to GMV Aerospace and Defence, Spain.
The contract was signed by ESA Director of Navigation Paul Verhoef and Jesús B. Serrano Martínez, CEO of GMV, in a ceremony hosted at Spain’s Ministry of Science, Innovation and Universities in Madrid, in the presence of Spanish Science Minister and former ESA astronaut Pedro Duque.
The ground control contract was signed Sept. 6 at at Spain’s Ministry of Science, Innovation and Universities in Madrid. From left: Verhoef; Secretary General of Transport of Spain’s Ministry of Public Works, María José Rallo, representing Spain in the EU Committee on Satellite Navigation Programmes; Spanish Science Minister and former ESA astronaut Pedro Duque; European Commission adviser on navigation activities Augusto González; and Martínez. (Photo: ESA)
Galileo’s Control Segment is hosted at the Oberpfaffenhofen Control Centre in Germany, with a “hot backup” in place at Galileo’s second Control Centre, at Fucino in Italy. It also extends to a network of Telemetry, Tracking and Control (TT&C) ground stations placed around the globe to stay linked with all satellites in the constellation.
The combination of these Control Centres plus TT&C stations are vital to keep Galileo running at its highest possible performance level. They monitor the overall status of the constellation, gather telemetry and uplink telecommands to each satellite, while also performing two-way radio and Doppler ranging to keep precise track of their position in space, identifying any orbital drift that might degrade the system’s accuracy.
The Galileo Control Segment has been designed to allow the automatic execution of routine operations. It also includes elements supporting flight dynamics analyses, constellation operations short-term planning as well as operations preparation.
Galileo’s global ground segment. (Map: ESA)
This first work order for the “Galileo Control Segment Exploitation Phase” contracts GMV Aerospace and Defence as prime contractor to undertake all necessary activities to upgrade the Galileo Control Segment as part of Galileo’s Exploitation phase.
This work includes upgrading the system architecture to manage a constellation of up to 41 Galileo satellites, updating obsolescent elements in the current system, improving operability linked to the provision of services and the addition of a new, second TT&C station to be based in Kourou, French Guiana.
The integration, qualification, deployment and migration into operational service of the various segments of the upgraded Galileo Control Segment will be undertaken over the next three years.
The Galileo ground station near New Caledonia capital Nouméa incorporates a Galileo Sensor Station (foreground) that monitors the quality of navigation signals and an uplink station (background) to relay navigation corrections to the satellites for rebroadcast to users. An antenna 13 meters in diameter for controlling the satellites has also been built, ready to come online later this year. (Photo: ESA)
This process is to undertaken while maintaining coherence with the other segments of the overall Galileo system – such as the Galileo Mission Segment which oversees Galileo services, the external control centres that carry out initial satellite switch-ons and in-orbit testing and the satellite platform and payload manufacturers, OHB System AG in Germany and Surrey Satellite Technology Ltd in the UK.
ESA has issued this work order in its role overseeing Galileo’s deployment, the design and development of future upgrades and the technical development of infrastructure on behalf of the European Commission, Galileo’s owner.
As Galileo, BeiDou, the Quasi-Zenith Satellite System, the Indian Regional Navigation Satellite System, and a variety of satellite-based augmentation systems join GPS and GLONASS, we help celebrate the coming 25th anniversary of the IGS as a truly multi-GNSS service.
Editor’s note: Tables 1 and 3 in the print version of this article contain some incorrect values and missing designators. These errors have been corrected in the tables below.
INNOVATION INSIGHTS by Richard Langley
A QUARTER OF A CENTURY. That is how old the International GNSS Service (IGS) will be on Jan. 1, 2019. Conceived in the early 1990s as the International GPS Service for Geodynamics, the IGS continues to be the global standard bearer in providing receiver data, satellite orbit and clock products and other resources with the highest possible precision and accuracy. I remember the discussions that took place at international conferences about the need for such a service to provide the necessary data to advance our understanding of plate tectonics and other Earth-related phenomena. And this was well before GPS was officially declared fully operational in 1995. Remember, surveyors and geodesists were early adopters of GPS, making use of the technology even when only a partial GPS constellation was in place.
The initial ideas for the IGS were laid out in an article published in GPS World in February 1993 entitled “Geodynamics: Tracking Satellites to Monitor Global Change.” But the services provided by the IGS extended well beyond the needs of the geodynamics research community, and so its name was shortened to just the International GPS Service. When GLONASS data and products became available, the name was further changed to its current moniker.
One of the IGS’s notable achievements has been in advancing GNSS standards such as the Receiver-Independent Exchange format for receiver data and other information. The need for such a standard was clear even before the formation of the IGS, and it was documented in this column in the July 1994 issue of GPS World (“RINEX: The Receiver-Independent Exchange Format”). We continued to cover the evolution of the IGS over the years with, for example, the article “The International GNSS Service: Any Questions?” in the January 2007 issue of the magazine.
And now, as Galileo, BeiDou, the Quasi-Zenith Satellite System, the Indian Regional Navigation Satellite System, and a variety of satellite-based augmentation systems join GPS and GLONASS, we help celebrate the coming 25th anniversary of the IGS as a truly multi-GNSS service.
For going on 25 years, the International GNSS Service (IGS) has carried out its mission to advocate for, and provide, freely and openly available high-precision GNSS data, as well as derived operational data products, including satellite ephemerides, Earth rotation parameters, station coordinates and clock information. The IGS is a self-governed, voluntary federation of more than 300 contributing organizations from more than 100 countries around the world that collectively operate a global infrastructure of tracking stations, data centers and analysis centers to provide high-quality GNSS data products. The IGS products are provided openly for the benefit of all scientific, educational and commercial users.
The IGS was first approved by its parent organization, the International Association of Geodesy (IAG), at a scientific meeting in Beijing, China, in August 1993. A quarter of a century later, the IGS community gathers for a workshop in Wuhan, China, this November to blaze a path to multi-GNSS through global collaboration.
As a key component of the IAG’s global geodetic infrastructure, the IGS contributes to, extends and densifies the International Terrestrial Reference Frame (ITRF) of the International Earth Rotation and Reference Systems Service (IERS). The ITRF provides an accurate and consistent spatial frame for referencing positions at different times and in different locations around the world.
In addition, IGS products enable the use of GNSS technologies for scientific applications such as the monitoring of solid Earth deformations, monitoring of Earth rotation and variations in the liquid Earth, and for scientific satellite orbit determinations, precise timing, ionosphere monitoring and water vapor measurements.
IGS products are also considered critical by surveying, geomatics and geo-information users around the world, who rely on them on a daily basis to improve efficiency. Many applications that require reliable, accurate GNSS positioning in construction, agriculture, mining, exploration and transportation also benefit from the IGS.
Community Collaboration
At the heart of the IGS is a strong culture of sharing expertise, infrastructure and other resources for the purpose of encouraging global best practices for developing and delivering GNSS data and products all over the world. The collaborative nature of the IGS community leverages this diversity to integrate and make full use of all available GNSS technologies while promoting further innovation.
More than 15,000 geodetic community members, some of whom comprise the backbone of the worldwide geodetic community, ensure that new technologies and systems are integrated into operational IGS products. Responsive to this innovation, the IGS develops and publicly releases standards, guidelines and conventions for the collection and use of GNSS data and the aforementioned products.
The IGS strives to maintain an international federation with committed contributions from its members. Participation of individuals and organizations is often driven by user needs, a key characteristic of the inclusive culture within the IGS.
Structure of the IGS
The IGS consists of a central bureau, a global network of GNSS stations, data and analysis centers and a number of working groups all coordinated and overseen by a governing board.
Central Bureau. The IGS Central Bureau (CB) functions as the secretariat of the IGS, providing continuous management and technology to sustain the multifaceted efforts of the IGS in perpetuity. The CB responds to the directives and decisions of the IGS governing board. It coordinates the IGS tracking network and operates the CB information system, the principal information portal where the IGS web, FTP and mail services are hosted (www.igs.org). The CB also represents the outward face of IGS to a diverse global user community, as well as the general public. The CB office is hosted at the California Institute of Technology/Jet Propulsion Laboratory in Pasadena, California. It is funded principally by the U.S. National Aeronautics and Space Administration (NASA), which generously contributes significant resources to advance the IGS.
The IGS Network. The foundation of the IGS is a global network of more than 500 permanent and continuously operating stations of geodetic quality. These stations track signals from GPS, and increasingly also track signals from GLONASS, Galileo, BeiDou, the Quasi-Zenith Satellite System (QZSS), the Indian Regional Navigation Satellite System (IRNSS; also known as NavIC: Navigation with Indian Constellation), as well as space-based augmentation systems (SBAS).
FIGURE 1 shows the recent state of the IGS network, indicating which stations are GPS only, GPS+GLONASS and multi-GNSS. FIGURE 2 is a photo of the IGS station ARHT at McMurdo Station, Antarctica.
FIGURE 1 . The extent of the IGS network in 2017, showing the locations of stations monitoring just GPS, GPS and GLONASS, and GPS and GLONASS plus at least one other constellation. (Map: IGS)FIGURE 2. The consistency of the final GPS satellite orbit solutions from individual IGS analysis centers over the past 25 years. Each line depicts the solution of one analysis center, as compared to the weighted mean. COD: Center for Orbit Determination in Europe, EMR: Natural Resources Canada (formerly Energy, Mines and Resources Canada), ESA: European Space Agency, GFZ: GeoForschungsZentrum (German Research Centre for Geosciences); GRG: Centre National d’Etudes Spatiales (Groupe de Recherche de Géodésie Spatiale); JPL: Jet Propulsion Laboratory; MIT: Massachusetts Institute of Technology; NGS: National Geodetic Survey; SIO: Scripps Institution of Oceanography; IGR: IGS rapid product. (Graph courtesy of T. Herring, MIT and M. Moore, Geoscience Australia)
The IGS is a critical component of the IAG’s Global Geodetic Observing System (GGOS), where it encourages and advocates for geometrical linkages of GNSS with other precise geodetic observing techniques, including satellite and lunar laser ranging, very long baseline interferometry and Doppler Orbitography and Radio Positioning Integrated by Satellite (DORIS). These linkages are fundamental to generating and accessing the ITRF.
Data and Analysis Centers. Lots of hard work and dedication from IGS contributing organizations goes into the fabrication of IGS products, which start at the tracking network, then are collected by data centers and sent to analysis centers. At these centers, the data are compared and combined by the analysis center coordinator, and finally made available as IGS products.
The IGS ensures high reliability by building redundancy into all of its components. In 1994, the IGS started with a network of about 40 stations; today, more than 500 receivers are included in the network. Critical to this activity are three categories of data center — operational, regional and global. At the ground level are operational data centers, which are in direct contact with IGS tracking sites and are responsible for such efforts as station monitoring and local archiving of GNSS tracking data. Operational data centers also validate, format, exchange and compress data. Regional data centers then collect tracking data from multiple operational data centers or stations, maintaining a local archive and providing online access to their data.
The six global data centers receive, retrieve, archive and provide online access to tracking data from operational and regional data centers. These global data centers are also responsible for archiving and backing up IGS data and products, and maintaining a balance of data holdings across the IGS network.
Analysis centers then receive and process tracking data from one or more data centers to generate IGS position, orbit and clock products. These products are produced in ultra-rapid, rapid, final and reprocessed versions for each analysis center.
FIGURE 3 shows the huge improvement in the precision and accuracy of the final orbit submissions from the analysis centers over the past 25 years.
Associate analysis centers produce specialized products, such as ionospheric information, tropospheric parameters or station coordinates and velocities for global and regional sub-networks. Regional and global network associate analysis centers complement this work as new capabilities and products emerge within the IGS.
FIGURE 3. The antenna of IGS station ARHT at McMurdo Station, Antarctica. (Photo: IGS)
Products from each analysis center are then combined into a single set of orbit and clock products by the analysis center coordinator, who monitors and assists the activities of analysis centers to ensure IGS standards for quality control, performance evaluation and analysis are successfully executed. The different analysis solutions ultimately verify the accuracy of IGS products, provide important redundancy in the case of errors in a particular solution, and average out modeling deficiencies of a particular software package.
TABLE 1 shows the quality of service characteristics of the various IGS GPS and GLONASS orbit and clock products. Similarly, TABLES 2, 3 and 4 show the characteristics of the tracking station coordinates, Earth rotation parameters and atmospheric parameters. See www.igs.org/products for further details.
TABLE 1. Quality of service characteristics for IGS orbit and clock products relating to GPS and GLONASS satellite orbits and satellite (sat.) and station (stn.) clocks as of 2017. (Data: IGS)TABLE 2. Quality of service characteristics for tracking station positions and velocities. (Data: IGS)TABLE 3. Quality of service characteristics for Earth rotation parameters: polar motion coordinates and rates of change and length-of-day (µas = microarcsecond). (Data: IGS)TABLE 4. Quality of service characteristics for atmospheric parameters: tropospheric zenith path delay and gradients and global grids of total electron content. (Data: IGS)
Working Groups and Projects
The IGS technical working groups (WGs) focus on topics of particular interest to the IGS, and consider various aspects of product generation and monitoring. The current working groups of the IGS span topics from antennas to tide gauges.
Antenna Working Group. To increase the accuracy and consistency of IGS products the Antenna WG coordinates research on GNSS receiver and satellite antenna phase-center determination. The group manages official IGS receiver and satellite antenna files and their formats.
Bias and Calibration Working Group. Different GNSS observables are subject to different satellite biases, which can degrade the IGS products. The Bias and Calibration WG coordinates research in the field of GNSS bias retrieval and monitoring.
Clock Products Working Group. This group is responsible for aligning the combined IGS products to a highly precise timescale traceable to the world standard: Coordinated Universal Time (UTC). The IGS clock product coordinator forms the IGS timescales based on the clock solutions of IGS analysis centers, and IGS rapid and final products are aligned to these timescales.
Data Center Working Group. The Data Center WG works to improve the provision of data and products from the operational, regional and global data centers, and recommends new data centers to the IGS governing board.
Joint GNSS Monitoring and Assessment Working Group. This working group, in conjunction with a joint trial project with International Committee on GNSS’s (ICG) International GNSS Monitoring and Assessment (IGMA) Task Force, seeks to install, operate and further develop a GNSS Monitoring and Assessment Trial Project.
GNSS Performance Monitoring ICG-IGS Joint Trial Project. The quality of navigation signals enables numerous applications, including worldwide time and frequency transfer and GPS meteorology. This project of the IGMA task force, coordinated in partnership with the IGS, focuses on monitoring GNSS constellation status.
Ionosphere Working Group. This group produces global ionosphere maps of ionosphere vertical total electron content (TEC). A major task of the Ionosphere WG is to make available global ionosphere maps from the TEC maps produced independently by ionosphere associate analysis centers within the IGS.
FIGURE 4 shows an example TEC map recomputed from data collected on March 17, 2015. The large values of TEC in the ionosphere’s equatorial anomaly are plainly visible.
FIGURE 4. An example total electron content map recomputed from data collected on March 17, 2015. TECU: total electron content units. (Image: IGS)
Multi-GNSS Working Group. This group supports the Multi-GNSS Experiment (MGEX) Project by facilitating estimation of intersystem biases and comparing the performance of multi-GNSS equipment and processing software. The MGEX Project was established to track, collate and analyze all available GNSS signals including those from BeiDou, Galileo and QZSS in addition to GPS and GLONASS.
Reference Frame Working Group. This working group combines solutions from the IGS analysis centers to form the IGS station positions and velocity products, and Earth rotation parameters for inclusion in the IGS realization of ITRF. A new reference frame, called IGS14, was adopted on Jan. 29, 2017 (GPS Week 1934). At the same time, an updated set of satellite and ground antenna calibrations, igs14.atx, was implemented.
Real-Time Working Group. The Real-Time WG supports the development and integration of real-time technologies, standards and infrastructure to produce high-accuracy IGS products in real time. The group operates the IGS Real-Time Service (RTS) to support precise point positioning (PPP) at global scales, in real time.
RINEX Working Group. The RINEX-WG jointly manages the Receiver-Independent Exchange (RINEX) format with the Radio Technical Commission for Maritime Services Special Committee 104 (RTCM-SC104). RINEX has been widely adopted as an industry standard for archiving and exchanging GNSS observations, and newer versions support multiple GNSS constellations. Recently, the IGS governing board agreed to adopt the official RINEX V3.04 format, handling the ability for nine-character station ID and fixing the definition of GNSS reference time scales.
Space Vehicle Orbit Dynamics Working Group. This group brings together IGS groups working on orbit dynamics and attitude modeling of spacecraft. This work includes the development of force and attitude models for new GNSS constellations to fully exploit all new signals with the highest possible accuracy.
Troposphere Working Group. The Troposphere WG supports development of IGS troposphere products by combining troposphere solutions from individual analysis centers to improve the accuracy of PPP solutions. The goal of the Troposphere WG is to improve the accuracy and usability of GNSS-derived troposphere estimates.
Tide Gauge (TIGA) Working Group. When studying sea level changes, where the GPS height of the benchmark is used for defining an absolute sea-level datum, problems occur when correcting the time series for height changes of the benchmark. TIGA is a pilot study for establishing a service to analyze GPS data from stations at or near tide gauges in the IGS network to support accurate measurement of sea-level change across the globe.
A Multi-GNSS IGS Network
The development of a multi-GNSS sub-network within the greater IGS network, led by the MGEX Project, develops the IGS’s capability to operate with multiple GNSS constellations. It has 223 multi-GNSS-capable (GPS + GLONASS + at least one other constellation) stations. Also, the number of IGS stations capable of real-time data streaming in support of the IGS Real-Time Project has increased to 195.
MGEX was founded in 2012 to build a network of GNSS tracking stations, characterize the space segment and user equipment, develop theory and data-processing tools, and generate data products for emerging satellite systems. The stations within its network contain a diverse assortment of receiver and antenna equipment, which are recognized and characterized by the IGS in equipment description files. Other than GPS and GLONASS, no combination process has yet been implemented within IGS for precise orbit and clock products of the other, newer, constellations. Despite this, cross-comparison among analysis centers, as well as with satellite laser ranging, has been used to assess the precision or accuracy for various products.
The growing role of multi-GNSS within the IGS network was benchmarked by the transition of MGEX to official IGS project status in 2016. For the sake of consistency, and as a nod to its heritage, use of the acronym “MGEX” has been retained.
Making Strides in Real Time
Through the Real-Time Service (RTS), the IGS extends its capability to support applications requiring real-time access to IGS products. The RTS is a GNSS orbit and clock correction service that enables PPP and related applications, such as time synchronization and disaster monitoring, at worldwide scales. The RTS is based on the IGS global infrastructure of network stations, data centers and analysis centers that provide world-standard high-precision GNSS data products.
The RTS is currently offered as a GPS-only operational service, but GLONASS is initially being offered as an experimental product for the development and testing of applications. GLONASS will be included within the service when the IGS is confident that a sufficient number of analysis centers can ensure solution reliability and availability. Other GNSS constellations will be added as they become available.
Engagement with the United Nations
The IGS engages with diverse organizations, outside of the immediate precise GNSS community, that have an interest in geodetic applications of GNSS. Notably, the IGS has supported the development of the Global Geodetic Reference Frame resolution, roadmap and implementation plan within the United Nations Global Geospatial Information Management (GGIM) Committee of Experts.
The IGS also works with the United Nations Office for Outer Space Affairs (UNOOSA) International Committee on GNSS (ICG) to develop common understandings of the requirements for multiple system monitoring through the joint pilot project with the ICG’s IGMA subgroup. The IGS also co-chairs ICG Working Group D, which focuses on reference frames, timing and applications.
A Multi-GNSS Future
Though the accuracy of current IGS multi-GNSS products lags behind standard IGS products for GPS and GLONASS, multi-GNSS paves the way for complete exploitation of new signals and constellations in navigation, surveying, geodesy and remote sensing.
IGS also looks externally to other techniques through its participation in the IAG’s GGOS, which has illuminated how satellite laser ranging observations to GNSS satellites improves our understanding of observational errors and thus drives further improvement of IGS position, clock and orbit products.
As it enters its second quarter-century, the IGS is evolving into a truly multi-GNSS service. For 25 years, IGS data and products have been made openly available to all users for use without restriction, and continue to be offered free of cost or obligation. In turn, users are encouraged to participate within the IGS, or otherwise contribute to its advancement.
Acknowledgements
The authors gratefully acknowledge the contributions of the IGS governing board and associate members in the drafting of this article. Special thanks to Anna Riddell and Grant Hausler, who, along with Gary Johnston, have an extensive chapter on IGS in the Springer Handbook of Global Navigation Satellite Systems, published in 2017 by Springer (see Further Reading). This book chapter is the new recommended official citation for publications referencing IGS data, products and other resources.
Allison Craddock a member of the Geodynamics and Space Geodesy Group in the Tracking Systems and Applications Section at the NASA Jet Propulsion Laboratory in Pasadena, California. She is the director of the IGS Central Bureau, manager of external relations for the International Association of Geodesy’s Global Geodetic Observing System, and staff member of the NASA Space Geodesy Program.
Gary Johnston is the head of the National Positioning Infrastructure Branch at Geoscience Australia. Johnston is the chair of the IGS governing board and the co-chair of the Subcommittee on Geodesy under the United Nations Global Geospatial Information Management committee of experts.
FURTHER READING
GNSS Handbook Chapter on IGS
“The International GNSS Service” by G. Johnston, A. Riddell and G. Hausler, Chapter 33 in Springer Handbook of Global Navigation Satellite Systems, edited by P.J.G. Teunissen and O. Montenbruck, published by Springer International Publishing AG, Cham, Switzerland, 2017.
International GNSS Service Technical Report 2017 (IGS Annual Report), edited by A. Villiger and R. Dach, published by IGS Central Bureau and University of Bern, Bern Open Publishing, Bern, Switzerland, 2018, doi: 10.7892/boris.116377. Includes reports from analysis centers, data centers and working groups.
“The Multi-GNSS Experiment (MGEX) of the International GNSS Service (IGS) – Achievements, Prospects and Challenges by O. Montenbruck. P. Steigenberger, L. Prange, Z. Deng, Q. Zhao, F. Perosanz, I. Romero, C. Noll, A. Stürze, G. Weber, R. Schmid, K. MacLeod and S. Schaer in Advances in Space Research, Vol. 59, No. 7, April 1, 2017, pp. 1671–1697, doi: 10.1016/j.asr.2017.01.011.
“Data Formats” by O. Montenbruck and K. MacLeod, Annex A in Springer Handbook of Global Navigation Satellite Systems, edited by P.J.G. Teunissen and O. Montenbruck, published by Springer International Publishing AG, Cham, Switzerland, 2017.
China launched two more BeiDou satellites on Aug. 25. (Photo: CCTV)
China successfully sent twin BeiDou navigation satellites into space on Aug. 25, aboard a single carrier rocket, according to news reports. The satellites are numbers 35 and 36 in the BeiDou navigation constellation.
Only a few weeks ago, China launched another pair of BeiDou-3 navigation satellites.
The Long March-3B carrier rocket lifted off from Xichang Satellite Launch Center in Southwest China’s Sichuan Province at 7:52 a.m. local time.
This was China’s 23rd orbital launch this year, surpassing the national record of 22 launches set in 2016. China Aerospace Science and Technology Corporation (CASC), the main contractor for the space program, is planning on 35 launches this year.
China launched two more BeiDou satellites on Aug. 25. (Photo: CCTV via Weibo)
The first GPS III satellite has been delivered to Florida for launch in December on a SpaceX rocket.
On Aug. 20, Lockheed Martin shipped GPS III SV01 to Cape Canaveral. GPS III SV01 is the first of 10 new GPS III satellites being built under U.S. Air Force contract and in full production at Lockheed Martin.
Designed and built at Lockheed Martin’s GPS III Processing Facility near Denver, the satellite was transported in a custom container from the Buckley Air Force Base in Colorado to the cape on a massive Air Force C-17 Globemaster III aircraft originating from Joint Base Lewis-McChord, Washington. On Aug. 21, it arrived at the Space Coast Regional Airport in Titusville, Florida.
The first GPS III satellite is loaded aboard a U.S. Air Force C-17 at Buckley AFB, Colorado, to begin processing for a December launch aboard a SpaceX rocket from Cape Canaveral. (Photo: U.S. Air Force/Lt. Col. Erin Gulden)
Start the Clock. The delivery of Satellite Vehicle 01 (SV01) starts the clock for final testing and checkout of the space vehicle prior to launch. The satellite will be processed at the Astrotech Space Operations Florida facility.
A government and contractor team will ensure the integrity of the satellite after shipment by performing a Mission Readiness Test to verify the health and safety of the vehicle, as well as communication compatibility with the ground operations center.
The team will then prepare for propellant loading and encapsulate the satellite in its protective fairing. At the completion of these activities, the satellite will be headed for a first-of-its-kind horizontal integration with the SpaceX Falcon 9 launch vehicle.
GPS III improvements. GPS III will be the most powerful and resilient GPS satellite ever put on orbit. Developed with an entirely new design, for U.S. and allied forces it will have three times greater accuracy and up to eight times improved anti-jamming capabilities over the previous GPS II satellite design block, which makes up today’s GPS constellation.
GPS III also will be the first GPS satellite to broadcast the new L1C civil signal. Shared by other international global navigation satellite systems, like Galileo, the L1C signal will improve future connectivity worldwide for commercial and civilian users.
“The shipment of the first GPS III satellite to the launch processing facility is a hallmark achievement for the program,” said Lt. Gen. John F. Thompson, U.S. Air Force’s Space and Missile Systems Center (SMC) commander and program executive officer for Space. “The modernization of GPS has been an outstanding collaborative effort and this brings us another step closer to launch.”
Vespucci. The satellite is dubbed “Vespucci” in honor of Amerigo Vespucci, the Italian explorer for whom the Americas were named.
The transportation crew consisted of both contractor and government personnel who oversaw the entire operation to ensure that the conditions of the transport environment would not damage any of the satellite’s sensitive components, the Air Force said.
“While the launch of the last GPS IIF satellite marked the end of an era, the upcoming GPS III launch will be the start of a brand new one,” said Col. Steven Whitney, director of the GPS Directorate. “It is the first of our new GPS III satellites, first to integrate with a SpaceX rocket, first to interact with elements of GPS’ Next Generation Operational Control System (OCX) Block 0, and first to have spacecraft acquisition and on-orbit checkout from Lockheed Martin facilities. We are excited to be at this point and we are ready for the upcoming launch of Vespucci.”
December Launch. The modernized GPS III SV01 is slated to launch in December. It will augment the current constellation of 31 operational GPS satellites. GPS delivers the gold standard in positioning, navigation, and timing services supporting vital U.S. and allied operations worldwide, and underpins critical financial, transportation and agricultural infrastructure that billions of users have come to depend on daily.
“Once on orbit, the modern technology of this first GPS III space vehicle will begin playing a major role in the Air Force’s plan to modernize the GPS satellite constellation,” said Johnathon Caldwell, Lockheed Martin’s program manager for navigation systems. “We are excited to start bringing GPS III’s new capabilities to the world and proud to continue to serve as a valued partner for the Air Force’s positioning, navigation and timing mission systems.”
On Aug. 10, the National Space-Based Positioning, Navigation, and Timing (PNT) Advisory Board, the government’s GPS expert board, sent a letter to the National Executive Committee for Space-Based PNT (a multi-agency body that steers GPS policy) that concluded, “We strongly recommend your opposition to the Ligado proposal.”
The letter sprang from a unanimous vote five days earlier to oppose allowing Ligado Networks to use spectrum neighboring the GPS band for terrestrial communications.
Ligado possesses licenses to broadcast on two satellite bands located adjacent to the GPS frequencies. The company has been seeking permission from the Federal Communications Commission (FCC) to repurpose these licenses from satellite-based use to ground-based use from powerful tower transmitters.
Ligado said in May it would lower the power in its proposal for the 1526–1536 MHz band to 9.98 dBW to avoid interference with certified aviation receivers. However, the PNT Advisory Board reiterated its opposition, saying that even if the transmissions’ power was lowered to just under 10 watts, it “will create totally unacceptable interference for a great number of GPS users in the United States.”
From the Letter: “This risk is far too great, and far too many questions remain, for Ligado’s proposal to be approved. While there are many broadband alternatives (Ligado would be a very small percentage of this national asset), there is only one GPS. Any impairment to current and future uses is clearly contrary to the national interest. Therefore, implementation of their recently proposed ~10-watt operating scheme will create totally unacceptable interference for a great number of GPS users in the United States. In fact, despite power limits in their current amended application, it is probable they could still be allowed to increase this power over time. This would be even more destructive to GPS users.
“We believe avoiding degradation over at least 90 percent of the region near Ligado transmitters is the absolute minimum protection for GPS receivers in each class. This would be a hypothetical 90 percent Protection Evaluation. This is not an endorsement of this level since, of course, all users would prefer 100 percent protection. The Department of Transportation (DOT) Adjacent Band Compatibility (ABC) study is the only validated test to verify degradation at various received power levels.
“Those results inform that to insure degradation not exceed 10 percent of the Region (90 percent Protection) for High Performance receivers, either:
Ligado maximum power can be no more than .0036 watts at the 400-meter spacing they had earlier planned. Tolerable power would be 3/10ths of 1 percent of their proposed ~10 watts. Or
the closest spacing of Ligado transmitters is 20,000 meters (over 12 miles) for their proposed ~10 watt power level (see Figure 1).”
Figure 1. The PNTAB strongly believes that 90 percent is the minimum Area Protection Criterion (maximum 10 percent degradation). (Chart: PNT Advisory Board)
The U.S. Defense Advanced Research Projects Agency (DARPA) Microsystems Technology Office is soliciting research proposals for the development of a new class of atom-based systems using integrated photonics and trapped atoms to enable high-performance, robust, portable clocks and gyroscopes.
The military researchers are asking industry to develop relatively simple portable photonic integrated circuits (PICs) for high-performance position, navigation and timing (PNT) devices as an alternative to GPS for when satnav signals are not available.
A PIC or integrated optical circuit, similar to an electronic integrated circuit, integrates multiple photonic (having to do with light) functions, providing capabilities for information signals imposed on optical wavelengths, typically in the visible spectrum or near-infrared, 850–1650 nanometers.
A-PhI Program
The Atomic-Photonic Integration (A-PhI) program seeks to develop trapped-atom based, high-performance PNT devices, reducing the complexity of these atomic systems by using PICs. According to the DARPA document, the PICs will replace the optical assembly behind devices such as sensitive and accurate angle sensors and clocks, while still enabling the necessary trapping, cooling, manipulation and interrogation of atoms.
A-PhI aims to demonstrate that compact PICs can replace the optical bench of conventional free-space optics for high-performance trapped-atom gyroscopes and trapped-atom clocks without degrading the performance of the underlying physics package.
Physics
Atomic systems using trapped atoms have the potential to be made portable while maintaining their accuracy due to the atomic trap’s small size and the inherent isolation a trap offers an atomic system from the environment, especially from acceleration.
Currently, these systems are bulky, heavy, and not notably portable, because of the complexity of the optical systems used to create the trap.
In the past, efforts to miniaturize the hundreds to thousands of optical components in such benchtop systems have relied on removing optical elements, miniaturizing the remaining elements, and tightly integrating them in a small package.
The products deliver degraded performance with the need to maintain very tight optical alignment, causing both poor environmental robustness and poor tolerance to design errors. Effective miniaturized atomic systems cannot be achieved at a reasonable cost with this approach.
Recent developments in PIC research suggest that on-chip optical frequency combs based on microresonators, optical frequency synthesis, novel on-/off-chip coupling, wavelength demultiplexers, and on-chip phased arrays for dynamic manipulation of light fields can replace optical systems with readily manufacturable, low-cost chips without the alignment sensitivity of conventional free-space optics.
Gyroscopes
A-PhI also seeks to develop proof-of-concept trapped atom gyroscopes, a matter-wave analog of the interferometric fiberoptic gyroscope. Such a miniaturization effort could generate an order of magnitude improvement in angular sensitivity and dynamic range over current free-space products.
A-PhI hopes to develop portable, high-performance, navigation and timing systems: the miniaturization of the optics of atomic systems without a decrease in performance. Subsequent work, the RFP asserts, will be required to incorporate the necessary compact and robust lasers and electronics to achieve a fully functioning, high-performance, portable PNT system.
Sports data company STATSports is offering STATS GPS shirts to provide real-time GPS intelligence to athletes and coaches.
Wearing STATS GPS shirts, teams can monitor player metrics such as accelerations/decelerations, energy expenditure and count of zone entries, as well as time, distance and power thresholds.
The system uses a 50-Hz sampling frequency. It allows practitioners to monitor up to 100 players in real time and post session with more than 300 GPS, inertial measurement unit (IMU) and HR-derived metrics, the company said.
The shirts feature an embedded medical-grade ECG sensor that’s fully integrated with the GPS units, allowing for seamless real-time analysis with the STATS Dynamix online portal.
Customizable reports can include information on imbalance, cardiovascular metrics and running, explosive and brake symmetry.
GPS III Space Vehicle 02 (GPS III SV02) is complete, tested and expected to launch in 2019.
As the first Lockheed Martin-built GPS III satellite prepares to ship to the launchpad, the U.S. Air Force has declared that the second GPS III satellite is complete, fully tested and ready to launch.
In May 2017, the U.S. Air Force’s second GPS III satellite was fully assembled and entered into Space Vehicle (SV) single line flow when Lockheed Martin technicians successfully integrated its system module, propulsion core and antenna deck. (Photo: Lockheed Martin)
The Air Force’s “Available for Launch” declaration is the final acceptance of Lockheed Martin’s second GPS III Space Vehicle (GPS III SV02), declaring it technically sound and ready to launch.
GPS III SV02 will bring new capabilities to U.S. and allied military forces, and a new civil signal that will improve future connectivity worldwide for commercial and civilian users.
GPS III SV02 now awaits official call up for launch in Lockheed Martin’s GPS III Processing Facility clean room in Denver. In June, the Air Force officially called up its first GPS III satellite for launch.
“The first GPS III satellite, GPS III SV01, was declared ‘Available for Launch’ in September 2017,” said Johnathon Caldwell, Lockheed Martin’s program manager for Navigation Systems. “It is now being prepared for shipment to Cape Canaveral, Florida, for a launch before the end of the year. With two GPS III satellites now ready for launch, and the third GPS III expected to be ready by early next year, we’re building strong momentum. These satellites will soon begin modernizing the current GPS constellation with new capabilities and more advanced technology.”
On July 13, 2017, the U.S. Air Force’s second GPS III space vehicle (GPS III SV 02) successfully completed acoustic testing. (Photo: Lockheed Martin)
GPS III will be the most powerful GPS satellite ever on orbit. It will have three times better accuracy and up to eight times improved anti-jamming capabilities.
GPS III’s new L1C civil signal also will make it the first GPS satellite to be interoperable with other international global navigation satellite systems.
Lockheed Martin is now in full production on 10 GPS III satellites at its GPS III Processing Facility near Denver.
In June, GPS III SV03 completed thermal vacuum testing, strenuous environmental trials simulating operations in the harshest space environments. In May, the antenna deck was added to GPS III SV04, fully integrating it into a complete satellite ready to begin environmental testing.
Right behind GPS III SV04 on the production line, the fifth, sixth and seventh GPS III satellites are in component build-up. The fifth satellite has its navigation payload and is expected to be fully assembled later this summer. To date, more than 90 percent of parts and materials for all 10 satellites under contract have been received.
In April, the company submitted a proposal to the government to build up to 22 additional GPS III Follow On (GPS IIIF) satellites which would bring even further enhanced capabilities to the GPS constellation’s more than four billion users.
In July 2017, Lockheed Martin tested the deployment of the solar arrays for the U.S. Air Force’s second GPS III space vehicle (GPS III SV02). (Photo: Lockheed Martin)
Geneq Inc. has released the F90, a multi-constellation GNSS receiver with a high level of technology integration. The new product is designed to fulfill surveyors’ demands for performance, flexibility and cost-effectiveness.
The F90 tracks multiple constellations (GPS, GLONASS, Galileo and Beidou) and can maximize the acquisition and tracking process with all-in-view GNSS satellite frequencies, the company said.
Providing maximum performance for accuracy and real-time measurements, the F90 also supports real-time kinematic correction services, including the RTX service that can achieve centimeter accuracy without a base station.
The F90’s advanced technology ensures a high performance even in harsh environment such as under heavy canopy, Geneq said.
The F90 has an excellent combination of GNSS, 4G, Bluetooth and Wi-Fi antenna. With highly integrated Bluetooth, Wi-Fi and 4G network modules, and without affecting accuracy and efficiency, the innovative F90 GNSS receiver is light and small. Even with its magnesium-alloy casing, F90 weighs only 1 kilogram and measures 140 x 157 x 76 millimeters.
With its integrated highly sensitive E-bubble and new tilt survey algorithm, the F90 becomes a calibration-free GNSS receiver, Geneq said. It is immune to magnetic disturbance and free from the limitation of tilt angles so that it can be used to measure inaccessible points.
Equipped with an internal radio, enabling frequency band change from 410 to 470 MHz, the F90 can be used with different radio communication protocols. Another important feature is its integrated second-generation web user interfae control, which is fully compatible with all devices and all browsers.
The user will benefit the F90’s two smart hot swappable Lithium batteries (the same battery used with Geneq’s SXPad 1000P data collector), allowing uninterrupted field work for up to 10 hours.
