The contract will be awarded to a single bidder, the Air Force Space Command stated in the announcement posted on FedBizOpps.gov. The estimated dollar value of the acquisition is $10 billion including all options.
Phase 2 is planned as a single, predominantly fixed-price incentive-type contract awarded via full and open competition for production of 22 GPS III satellites. Deadline for proposals is April 16. Construction is to begin in fiscal year 2019 (Oct. 1, 2018), with delivery of the first satellite in 2026.
For Phase 1, AFSC awarded in May 2016 three fixed-price contracts to Boeing Network and Space Systems, Northrop Grumman Aerospace Systems and Lockheed Martin Space Systems Company, which is building the first 10 GPS III satellites. According to the Air Force, “Phase 1 has determined that viable, low-risk, high-confidence sources exist to conduct a full and open competition for Phase 2, the production of 22 GPS III SVs starting in the FY19 timeframe.”
Now the company has released from new tests using configurations with a differential source and with a more accurate OCXO clock, producing timing accuracy of 160 nanoseconds.
Gregory Gutt, president and chief technical officer of Satelles, made the presentation at the recent Institute of Navigation International Technical Meeting.
The 66-satellite Iridium LEO constellation transmits overlapping spot beams, which provide location-specific data that changes every few seconds. The featured image on this article (above) shows spot beam pattern for 2 of 66 satellites.
Overview of Satelles test configurations. (Chart: Satelles)
The testing employed three different configurations of equipment, services, and environment, as shown in the adjacent figure. Equipment employed in the tests included a Stanford Research Systems (SRS) rubidium vapor frequency reference, based on the PRS10 module, and a Satelles Evaluation Kit (EVK2) STL receiver, comprising a Maxim RF chip, Xylinx Spartan-3 FPGA , TI dual core DSP chip, and internal OCXO or external clock.
Parameters and equipment for the three test configurations:
Configuration #1 – Optimal. Outdoor antenna, Rubidium clock powered on for months prior to data collection, receiver configured in static mode with a known location, and high-quality antenna
Configuration #2 – Sub-optimal. Indoor antenna, Rubidium clock powered on 6 hours prior to data collection, receiver configured in static mode with an unknown location, and low quality antenna
Results from the first two tests are shown here:
Test results, configurations 1 and 2. (Chart: Satelles)
Configuration #3. Three independent receivers collecting data, receiver on-board OCXO, indoor antenna, receiver configured in static mode with an unknown location, low-quality antenna. Tests performed:
10 days with no local reference station running
10 days with local reference station, 20km away from test receivers, providing timing corrections to STL ground segment.
Results from these tests shown here:
Results from OCXO tests. (Table: Satelles)
With this individual test result:
OCXO timing result with base station. (Chart: Satelles)
Some of the commercially available products and evaluation kits that incorporate the STL service are shown here:
STL user equipment implementations. (Image: Satelles)
China continues to update the BeiDou navigation satellite system. On Feb. 12, two more navigation and positioning satellites were launched into medium Earth orbits, following the successful launch of a pair of BeiDou satellites on Jan. 11.
A Long March 3B rocket with a Yuanzheng-1 upper stage lifted off from the Xichang Satellite Launch Center, Sichuan Province, at 13:03 local time (05:03 UTC), according to gbtimes.com.
The launch had been set for the same window on Feb. 10, but was delayed by the visit of Chinese president Xi Jinping to the launch site.
Success of the mission was confirmed four hours after launch, following insertion of the satellites into their intended orbits, around 21,000 kilometers above the Earth.
The newly launched pair are BeiDou-3 28 and 29. The satellites are part of a third phase of Beidou deployment, which will take Beidou coverage from regional to covering the countries along the Belt and Road initiative by the end of 2018, and global by 2020.
According to Nasaspaceflight.com, the satellites are using a new bus featuring a phased array antenna for navigation signals and a laser retroreflector, with a launch mass of 1,014 kg.
The accuracy, stability and signal strength of the Beidou-3 satellites is improved over previous versions by developments in atomic clocks, laser communications and inter-satellite links.
The Long March 3B/YZ-1 carrying Beidou satellites 28 and 29 lifts off from Xichang Satellite Launch Centre at 13:03 local time on Feb. 12. (Photo: CNS)
Two methods of spoofer detection, the identification and sourcing of false GNSS signals, have been released by Javad GNSS, using features available for all of its OEM GNSS boards.
Spoofer detection and alarm. This feature then identifies and isolates the spoofer signal, ignores it, and provides a position solution using only valid satellite signals.
Determination of the direction from which the spoofing signals emanate. This can aid in tracking down the actual spoofing source.
Spoofer Detection
With 864 channels and roughly 130,000 quick-acquisition correlators, the Javad GNSS Triumph chip can assign more than one channel to each GNSS satellite, in order to find all the signals that are transmitted with that satellite’s PRN code. If the chip detects more than one reasonable and consistent correlation peak for any PRN code, it concludes that spoofing is present and can the proceed to identify the spoofed signals.
In this case, it uses the position solution provided by all other clean signals (L1, L2, L5, and so on, from all GNSS constellations — GPS, GLONASS, Galileo, Beidou, and mroe) to identify the spoofer signal and use the real satellite measurement. If all GNSS signals are spoofed or jammed, then the system issues an alarm, directing the user to ignore GNSS and use other sensors in an integrated system.
Satellite and Spoofer Peaks
The figure below shows an example of a spoofer signal and a real satellite signal received at a GNSS receiver. These screenshots are from a real spoofer in a large city. The bold numbers are for the detected peaks. The gray numbers represent highest noise, not a consistent peak. A “*” symbol next to the CNT numbers indicate that signal is used in position calculation. Each CNT count represent about 5 seconds of continuous peak tracking.
The first screenshot shows no spoofing is present. The second shows that all GPS satellites are being spoofed.
No spoofer. Only one reasonable peak for each satellite. (Table: Javad GNSS)Table: Javad GNSS
In the above screenshot all GPS satellites have two peaks and all are spoofed. We were able to distinguish the spoofer signal and use the real satellite signals in correct position calculation as indicated by the ”*” next to the CNT numbers.
GNSS Overall View
The following screenshot shows the status of all GNSS signals. The format and the signal definitions are explained below.
Table: Javad GNSS
Tracked: Tracked by the tracking channels and has one valid peak only.
Used: Used in position calculation.
Spoofed: Has two peaks. Good peak is isolated, if existed.
Blocked: Blocked by buildings or by jamming. If jammed, shows higher noise level.
Faked: Satellite should not be visible, or such PRN does not exist.
Replaced: Real signal is jammed and a spoofed signal put on top of it. Because of jammer, it shows higher noise level.
The U.S. Air Force plans to release a request for proposal (RFP) for the second phase of GPS III Follow-On satellite production “on or about” Feb. 13, according to a report by Inside Defense.
The RFP was expected in December 2017, but was held up as officials worked to solidify requirements.
The solicitation is expected to result in a contract for up to 22 GPS III Follow-On satellites in the 2019 time frame.
Lockheed Martin is on contract to build the initial 10 GPS III satellites, the first of which is expected to launch this year. Besides Lockheed, Boeing and Northrop Grumman have both expressed interest in competing to produce the next batch of satellites.
By Peter Steigenberger, Steffen Thoelert, André Hauschild, Oliver Montenbruck and Richard B. Langley
INNOVATION INSIGHTS with Richard Langley
POP QUIZ: What is the most populous metropolitan area in the world? According to Wikipedia, it is Tokyo. In fact, Japan has three cities in the list of the 50 largest cities in the world. Not only are there a lot of people in these cities, they also have many tall and densely packed buildings. And that’s a problem for GPS and the other global navigation satellite systems.
Radio signals travel in straight lines. Well, mostly so. At very low frequencies, radio waves propagate as ground waves and can achieve long-distance propagation in the waveguide formed by the surface of the Earth and the ionosphere. At slightly higher frequencies, such as those used by AM radio, signals still travel as ground waves. However, additionally, the signals propagate upwards as skywaves. During daylight hours, the D layer of the ionosphere absorbs the skywaves, but when the D layer dissipates at night, the higher ionospheric levels can reflect skywaves back to Earth allowing long-distance reception. And communication by shortwave is virtually all by ionosphere-bounce skywaves. Above 30 MHz or so, signals normally travel along line-of-sight raypaths. The atmosphere can slightly bend the raypath, but the signals essentially travel in straight lines. Of course, that’s what makes GPS possible.
GPS works exceedingly well as long as a receiver’s antenna has a line-of-sight “view” of the satellites. Obstacles such as mountains and buildings block the relatively weak GPS signals. In concrete canyons, for example, that may leave a receiver with fewer than four satellites in view, meaning that 3D positioning is impossible. Even if four or more satellites are visible, they may be bunched together in the sky, resulting in high dilution of precision values and potentially large position errors.
In an effort to alleviate the GPS positioning problem in both urban and mountainous areas of Japan, the Japanese government has developed the Quasi-Zenith Satellite System (QZSS). A constellation of three inclined geosynchronous orbit (IGSO) satellites and one geostationary satellite transmits GPS-compatible signals to enhance positioning availability and accuracy. The IGSO satellites have repeating figure-eight ground tracks with the satellites spending most of their one-sidereal-day orbit, centered around apogee, over the Japanese archipelago. The satellites sequentially hover in the sky near the zenith for long periods of time. The satellites also provide both standard and advanced augmentation signals.
The first, or prototype, Block I QZSS satellite was launched in 2010 and, based on the positive test results from this satellite, an additional three satellites were launched in 2017, completing a four-satellite constellation. In this month’s column, we examine the recent developments of this unique and innovative navigation system.
With the launch of two additional spacecraft in August and October 2017, the Japanese Quasi-Zenith Satellite System (QZSS) reached the goal of a four-satellite constellation with the first fully-operational services expected to start in 2018. Aug. 19, 2017, marked the launch of QZS-3, the first geostationary Earth orbit (GEO) QZSS satellite, while the third spacecraft in inclined geosynchronous orbit (IGSO), QZS-4, was subsequently launched on Oct. 10, 2017. An artist’s view of the constellation is shown in FIGURE 1.
FIGURE 1. An artist’s view of the QZSS satellites. The upper-most satellite is the geostationary QZS-3 spacecraft with the additional S-band dish antenna whereas the other satellites pictured are the inclined geosynchronous satellites. (Image: Mitsubishi Electric)
Table 1 lists the four satellites of the current QZSS constellation. Whereas the first generation Block I satellite QZS-1 was launched in 2010, the three Block II satellites joined the constellation in 2017.
Table 1. QZSS constellation as of December 2017. SVN: space vehicle number, PRN: pseudorandom noise (code number), IGSO: inclined geosynchronous orbit, GEO: geostationary Earth orbit.
The most obvious visual difference between the QZSS Block I and II satellites is the different number of subpanels for the solar arrays: three for the Block I satellite and two for the Block II satellites with spanned widths of 25.3 meters and 19.0 meters, respectively. The reduced size of the Block II array has been achieved through the use of new, high-efficiency solar cells. The GEO satellite in addition carries S- and Ku-band antennas with diameters of 3.2 meters and 1.0 meter, respectively. While the IGSO satellites are equipped with a helix antenna array for transmission of the main L-band navigation signals, the GEO satellite uses a patch antenna array similar to that of the Galileo satellites.
The ground tracks of the four QZSS satellites are plotted in FIGURE 2. The ground tracks of all of the IGSO satellites have the characteristic figure-eight shape due to the large orbit eccentricity of 0.075 and results in a longer visibility period for users in the northern hemisphere. The ground tracks do not precisely match, however. QZS-1 and QZS-4 have similar orbit inclinations (with respect to the equator) of 40.9° and 40.5°. QZS-2, on the other hand, has a larger inclination of 44.5°, which leads to a wider extension of the ground track in the north-south direction.
FIGURE 2. Ground tracks of the four-satellite QZSS constellation as of Dec. 4, 2017. The blue square indicates the sub-satellite point of the geostationary QZS-3 satellite. (Image: Authors)
Also, the central longitude of the ground tracks, which marks the center of the figure-eight shape, varies between 130° and 140° E. These differences are still within the tolerances defined in the QZSS Interface Specification, version 1.8 of Oct. 3, 2016, which specifies the inclination to be 43° ± 4° and the central longitude of the ground track to be 135° ± 5° E. The GEO satellite QZS-3 is located at 127° E and has been controlled to stay within a 0.1° inclination window since achieving its initial orbit.
All QZSS satellites transmit navigation signals in the L1, L2 and L5 bands compatible with GPS, namely L1 C/A, L1C, L2C and L5 (the Positioning, Navigation and Timing or PNT service). QZSS-specific signals are transmitted in the L1, L5 and L6 bands: the Sub-meter Level Augmentation Service or SLAS (formerly, Submeter-class Augmentation with Integrity Function or SAIF) signals for all satellites on L1 and, in addition, on L5 for Block II satellites (see TABLE 2).
Table 2. QZSS signals. The L2C and CLAS signals use interleaved bit streams for concurrent transmission of two independent ranging sequences. The L1S signal consists of SLAS, a message service, and L1Sb, an SBAS signal. (Based on Table 11.2 in the Springer Handbook of Global Navigation Satellite Systems).
Starting in 2020, the GEO satellite will also provide a satellite-based augmentation system (SBAS) signal called L1Sb with range corrections and integrity information for aviation applications in particular. The SLAS and SBAS signals are transmitted via dedicated antennas but they are phase coherent with the GPS-compatible navigation signals transmitted via the main L-band antenna. The L6 signal provides the Centimeter Level Augmentation Service or CLAS (formerly, the L-band Experiment or LEX) on all QZSS satellites, but employs a different signal structure for Block I (L61) and Block II (L62). An overview of the various L-band signals and corresponding PRN assignments is given in TABLE 3. QZS-3 also provides the QZSS Safety Confirmation Service (Q-ANPI) to support rescue operations with S-band communication in case of a disaster. The total transmit power is 500 watts for the Block II IGSO satellites and 550 watts for the GEO satellite.
Table 3. PRN code assignment of QZSS satellites according to the interface specifications (see Further Reading). RINEX: PRN code in RINEX observation files; NAV: PRN code for L1 C/A, L1C, L2C and L5 navigation signals; NSTD: non-standard codes of IGSO/GEO satellites.
QZS-3/4 SIGNAL TRANSMISSION
Tracking of the QZS-3 L1 C/A and L5 signals by receivers in the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt or DLR) and International GNSS Service networks started on Sept. 10, 2017, at 09:04 UTC followed by the L1C and L2C signals at 09:27 UTC. L5 tracking started with a very low carrier-to-noise-density ratio (C/N0) of 10 – 20 dB-Hz that increased to 50 – 55 dB-Hz shortly after the activation of the L1C and L2C signals. QZS-3 broadcast ephemerides were first transmitted on Oct. 4, 2017, at 16:00 UTC. However, tracking of the L1, L2 and L5 navigation signals with common geodetic receivers is currently limited to receivers with experimental firmware versions developed by three different manufacturers.
Signal transmissions from QZS-4 started on Nov. 1, 2017. The first L1 C/A signals of PRN J03 were received at 02:50 UTC. At the same time, L5 signal transmission started but this signal was only tracked by a very limited number of receivers due to its low signal strength resulting in a C/N0 of only about 15 dB-Hz. At 03:14 UTC, an increase of the C/N0 by about 40 dB occurred and many additional receivers started tracking the L5 signal. At the same time, the L1C and L2C signals were also activated followed by the L1 SLAS signal at 03:20 UTC.
It is interesting to note that QZS-4 also transmitted the non-standard code J06 on different frequencies during its first weeks of operation. This code cannot be used for positioning and is used for test purposes or in case of system errors. Until Nov. 27, 2017, QZS-4 regularly switched between transmission of standard and non-standard codes. An example of such a switch for the station UNX200AUS located in Sydney, Australia, is shown in FIGURE 3. During this test period, several outages of individual or all navigation signals also occurred. Since Nov. 24, 2017, 5:00 UTC, broadcast ephemerides of QZS-4 have been available and transmission of the L5 SLAS signal started at 09:31 UTC.
FIGURE 3. QZS-4 signals tracked by DLR’s JAVAD Delta-3TH receiver in Sydney, Australia. The top plot shows the standard code PRN J03 and the bottom plot the non-standard code J06. The measured C/N0 is shown for L1 C/A (black), L1C (blue), L2C (red) and L5 (green). (Image: Authors)
FIGURE 4 shows the L-band normalized power spectra of QZS-2 and QZS-4. The spectra were obtained from in-phase (I) and quadrature (Q) data recorded with DLR’s 30-meter high-gain antenna in Weilheim, Germany. Almost identical characteristics can be seen for the signals of both satellites in the L1, L2 and L6 bands. However, in the L5 band, QZS-4 shows a slightly lower power than that of QZS-2 due to the lack of the L5 SLAS transmission during the data recording. Unfortunately, QZS-3 is not visible from Weilheim due to a longitude difference of more than 115°.
FIGURE 4. Normalized power spectra of QZS-2 and QZS-4 measured with DLR’s 30-meter high-gain antenna on July 18, 2017, and Nov. 7, 2017, respectively. (Image: Authors)
ATTITUDE
Usually, QZS-2 and QZS-4 follow a nominal yaw steering attitude with the spacecraft z-axis pointing towards the Earth and the y-axis (solar panel axis) oriented perpendicular to the plane defined by the locations of the satellite, the Sun, and the Earth. The maximum yaw rate of these satellites is limited to 0.055° per second and can be exceeded by the nominal yaw rate when the angle of the Sun with respect to the orbital plane (the beta angle, β) is between -5° and +5°. During orbit control maneuvers, the QZSS Block II IGSO satellites are operated in orbit normal mode with the z-axis pointing to the Earth and the y-axis perpendicular to the orbital plane. The geostationary QZS-3 satellite is continuously operated in orbit normal model while QZS-1 enters orbit normal mode for |β| < 20°.
Detailed information about the different attitude rules as well as spacecraft reference frame, mass, center of mass, phase center offsets and variations of the navigation antenna, laser retroreflector offsets, satellite group delays as well as the total transmit power of all four satellites is provided by the Cabinet Office, Government of Japan, in the QZSS satellite information documents.
Since all QZSS satellites are equipped with a separate L1 SLAS transmit antenna, which is mounted with an offset to the main L-band antenna, each satellite’s attitude can be directly estimated from single-difference carrier-phase observations between the two spacecraft antennas.
FIGURE 5 illustrates the attitude of QZS-4 estimated from L1 C/A and L1 SLAS observations from 10 tracking stations as well as the nominal yaw steering attitude. QZS-4 had a beta angle of about 11° on Dec. 9, 2017, confirming that this satellite does not enter orbit normal mode for |β| < 20° as does QZS-1. Differences between nominal yaw steering attitude and estimated attitude are usually within ±1.5° reflecting estimation errors as well as differences between nominal and true attitude.
FIGURE 5. Nominal yaw steering attitude (blue) and estimated attitude (red) of QZS-4 for Dec. 9, 2017 (β ≈ 11°). (Image: Authors)
CLOCK PERFORMANCE
The clock stability represented by the modified Allan deviation is given in the upper panel of FIGURE 6 for the QZSS IGSO satellites. The QZSS Block II IGSO satellites show an almost identical stability for integration periods up to 100 seconds. For longer periods, the QZS-2 clock seems to perform slightly better.
However, this effect is probably related to the number of stations contributing to the clock solutions of the individual satellites which differs by a factor of more than two. For comparison purposes, the Allan deviation of two Galileo rubidium clocks (GAL-101 and GAL-204) and a Galileo passive hydrogen maser (PHM, GAL-207) are plotted in the bottom panel of Figure 6.
Whereas the performance of the QZSS and Galileo rubidium clocks is very similar, the Galileo PHM is more stable by a factor of two to five over all integration periods.
FIGURE 6. Modified Allan deviations of the QZSS IGSO rubidium clocks, Galileo rubidium clocks (GAL-101 and GAL-204) and a Galileo passive hydrogen maser (GAL-207). (Image: Authors)
CONCLUSIONS
With the launch of the third IGSO spacecraft and the first GEO spacecraft, the QZSS constellation has reached a four-satellite configuration, which is required for the provision of operational augmentation services. QZS-3 and QZS-4 were declared useable for PNT, SLAS, and CLAS trial services on Dec. 18, 2017, and Jan. 12, 2018, respectively. Inclusion in the operational QZSS constellation is expected for 2018 and this will provide continuous visibility of three satellites in the service area. An expansion to a constellation of seven satellites is planned for 2023 including a Public Regulated Service for authorized users.
MANUFACTURERS
Data used in this article was collected using Javad GNSS Delta-G3TH, Trimble NetR9 and Septentrio PolaRx4 and PolaRx5 receivers.
Authors Peter Steigenberger, Steffen Thoelert, André Hauschild and Oliver Montenbruck are from the German Aerospace Center (DLR).
Richard B. Langley is from the University of New Brunswick and authors the monthly “Innovation” column for GPS World magazine.
FURTHER READING
• Quasi-Zenith Satellite System
“Quasi-Zenith Satellite System” part of “Regional Systems” by S. Kogure, A.S. Ganeshan and O. Montenbruck, Chapter 11 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.
“QZS-2 Signal Analysis, QZS-3 Launched” by S. Thoelert, A. Hauschild, P. Steigenberger, O. Montenbruck and R.B. Langley in GPS World, Vol. 28, No. 9, September 2017, pp. 10–14.
China launched two BeiDou-3 navigation satellites into space on Jan. 12 as part of efforts to enable its BeiDou system to provide navigation and positioning services to countries along the Belt and Road by the end of 2018. The Belt and Road Initiative aims to create the world’s largest platform for economic cooperation, encompassing China, Southeast Asia, South Asia, Central and Western Asia, Middle East and Africa, and Central and Eastern Europe.
The twin satellites are coded MEO-7 and MEO-8, the 26th and 27th satellites in the BeiDou Navigation Satellite System. They are based on a newly developed dedicated satellite bus that features a phased-array antenna for navigation signals and a laser retro-reflector. They each weigh about one metric ton, and both have two deployable solar arrays; their design life is 12 years. This was the first BeiDou launch in 2018, which will see an intensive further launch schedule throughout the year.
In his December 2017 “Directions” article in GPS World, Changfeng Yang, chief BeiDou system architect, wrote that “Eighteen BD-3 MEO satellites and one BD-3 GEO satellite will be launched by around the end of 2018. Upon the deployment of those 19 satellites, BD-3 will possess the initial operational capability and serve the countries along the Belt and Road.”
This would bring the constellation to an initial operational capability before the end of this year. China targets completion of the fully operational global system in 2020.
More interference potential from another tower set
Satellite operator Iridium asked the Federal Communications Commission (FCC) in April 2017 to modify its license to add a new class of ground stations called Certus for expanded terrestrial, maritime and aeronautical operations.
Iridium’s 66-satellite constellation provides, in addition to mobile communications signals, the Satelles time and location service: microsecond timing accuracy and 20- to 50-meter unaided position accuracy worldwide (see the “Innovation” column, July 2017 GPS World).
GPSIA. The GPS Innovation Alliance (GPSIA) commented in September, “GPSIA seeks to ensure that radio navigation satellite service (RNSS) receivers operating in the 1559–1610 MHz band are adequately protected from out-of-band emissions (OOBE) generated from the new Certus mobile Earth station (MES) terminals that will operate on the second-generation Iridium satellite system.
“GPSIA and Iridium are actively engaged in constructive discussions regarding the adequacy of that protection, but no final resolution has yet been reached. [….]
“In the unlikely event that GPSIA is unable to reach an agreement with Iridium, it asks the commission to impose limitations on the operation of Certus terminal devices to protect GPS/RNSS operations in the 1559–1610 MHz band at a level equivalent to what terrestrial terminals in the same and other frequency ranges provide at –95 dBW/MHz.”
Hexagon. Hexagon, the parent company of GPS manufacturer NovAtel, commented on Jan. 8, “Certain statements in the modification application regarding output power and amount of terminals to be deployed cause great concern regarding the unimpeded operation of radio navigation satellite service (RNSS) receivers. The application does not include enough information to simulate the impact properly.
“Hexagon politely requests that the FCC will exercise the same due diligence [as] during previous modification applications close to the RNSS bands (for example docket 11-109) and establish a technical working group or a similar testing process that ensures unimpeded coexistence of the modified Iridium terminals with the established RNSS systems.”
Documents related to the case can be found here, on the FCC International Bureau website.
Galileo security center moves to Spain
The Galileo Security Monitoring Centre (GSMC) for the European Union’s Galileo satellite system will move from the United Kingdom to Madrid, Spain, as a result of Brexit.
The center, not yet fully operational, is expected to grow to a staff of as many as 30. It controls access to the satellite system and provides around-the-clock monitoring when the main security center near Paris is offline.
The GSMC is operated by the European GNSS Agency. It is one of a number of EU institutions leaving the UK as a result of the 2016 referendum vote.
Spain has another of the fundamental centers of the program, the Loyola de Palacio GNSS Service Center, also in Madrid.
Researchers testing a satellite-based earthquake early warning system developed for the U.S. West Coast found that the system performed well in a “replay” of three large earthquakes that occurred in Chile between 2010 and 2015, reports the Seismological Society of America.
The results, reported in the journal Seismological Research Letters (SRL), suggest that such a system could provide early warnings of ground shaking and tsunamis for Chile’s coastal communities in the future.
The early warning module, called G-FAST, uses ground motion data measured by GNSS to estimate the magnitude and epicenter for large earthquakes — those magnitude 8 and greater. These great quakes often take place at subducting tectonic plate boundaries, where one plate thrusts beneath another plate, as is the case off the coast of Chile and the U.S. Pacific Northwest.
Using data collected by Chile’s more than 150 GNSS stations, Brendan Crowell of the University of Washington and his colleagues tested G-FAST’s performance against three large megathrust earthquakes in the country: the 2010 magnitude 8.8 Maule, the 2014 magnitude 8.2 Iquique, and the 2015 magnitude 8.3 Illapel earthquakes.
G-FAST was able to provide magnitude estimates between 40 to 60 seconds after the origin time of all three quakes, providing magnitude estimates that were within 0.3 units of the known magnitudes. The system also provided estimates of the epicenter and fault slip for each earthquake that agreed with the actual measurements, and were available 60 to 90 seconds after each earthquake’s origin time.
“We were surprised at how fast G-FAST was able to converge to the correct answers and how accurately we were able to characterize all three earthquakes,” Crowell said.
Most earthquake early warning systems measure properties of seismic waves to quickly characterize an earthquake. These systems often cannot collect enough information to determine how a large earthquake will grow and as a result may underestimate the earthquake magnitude—a problem that can be avoided with satellite-based systems such as G-FAST.
It’s difficult to test these types of early warning systems, Crowell noted, because magnitude 8+ earthquakes are relatively rare. “We decided to look at the Chilean earthquakes because they included several greater than magnitude 8 earthquakes, recorded with an excellent and consistent GNSS network. In doing so, we would be able to better categorize the strengths and weaknesses in G-FAST.”
ShakeAlert
The Chilean tests will play a part in furthering developing G-FAST for use in the U.S., where Crowell and colleagues have been working to include it in the prototype earthquake early warning system called ShakeAlert, now operating in California, Oregon and Washington. The Chilean earthquakes, Crowell said, represent about half of magnitude 8 events in the recorded catalog of earthquakes that are used to test G-FAST and other geodetic algorithms for inclusion in ShakeAlert.
Ten magnitude 8 or greater earthquakes have occurred along the Chilean coast in the past 100 years, including the 1960 magnitude 9.5 Valdivia earthquake, which is the largest earthquake recorded by instruments. “The hazard due to these large events is well recognized and understood,” in Chile, wrote Sergio Eduardo Barrientos of the Universidad de Chile, in a second paper published this week in SRL. “Return periods for magnitude 8 and above events are of the order of 80 to 130 years for any given region in Chile, but about a dozen years when the country is considered as a whole.”
After the 2010 Maule earthquake, the country began installing a network of digital broadband seismic and ground motion stations, GPS stations, and GNSS stations to provide accurate information for tsunami warnings and damage assessment. Since 2012, the Centro Sismológico Nacional at the Universidad de Chile has operated more than 100 stations, and has recently begun to operate almost 300 strong-motion accelerometers that measure ground shaking.
In a third paper published in SRL, Felipe Leyton of the Universidad de Chile and colleagues analyze data collected from 163 of these strong-motion stations to learn more about the local site conditions of underlying rock and soil in these areas. Site conditions can modify the shaking of large earthquakes and control the damage to buildings and other infrastructure caused by the shaking.
The new study “gives us a unique opportunity to improve our knowledge of the behavior of soil deposits during earthquakes, especially in urbanized areas,” write Leyton and colleagues, who say the data could be used to help improve building designs and codes.
A U.K. government report issued on Jan. 30 looks at the vulnerability of all satellite-based positioning systems: GPS, Galileo, GLONASS, BeiDou, QZSS and more. Issued by the Office of the Government Chief Scientific Adviser, Sir Mark Walport, and informally called the Blackett Report, designating the highest level of government scientific studies, named after a UK physicist who won the 1948 Nobel Prize, the review aims to “lay out the breadth, scale and implications of our reliance on ‘the invisible utility’ mainly in terms of existing critical national infrastructure (CNI).”
“Satellite-derived Time and Position: A Study of Critical Dependencies” states in the forward that it “represents a vital step in understanding the UK’s dependency on GNSS and recommends measures to improve our resilience. Importantly, it also recognises that innovation will be key to realising, fully and safely, the economic and societal benefits offered by GNSS.”
The report points to the fragility of satellite positioning signals which can be affected by cheap jammers, spoofers, weather and interference from other radio signals — among other vulnerabilities. The 86-page PDF document is downloadable here.
The review incorporates the results of a separate but related study, issued in April 2017, looking at the fiscal consequences of a GNSS disruption in. “Economic Impact to the U.K. of a Disruption in GNSS” was briefly summarized in a June 2017 column from this magazine (scroll down to “At What Cost Ignorance?”). The report attempted to quantify the cost of a GNSS disruption, should one occur. The authors came up a figure of 5.2 billion pounds ($6 billion) for a 5-day disruption.
David Last, a UK consultant engineer specializing in radio navigation and communications systems, professor emeritus at the University of Bangor, Wales and past president of the Royal Institute of Navigation, consulted on the June 2017 economic impact report, and was a member of the expert panel and co-author of the January 2018 Blackett Report. He was to have given a presentation on them at the ION International Technical Meeting in Reston, Virginia on January, but could not make the trip. The following materials are drawn from his prepared presentation.
Some of the conclusions from the June 2017 economic impact study are:
There are alternatives to GNSS, specific to each application
However, there is no universally-applicable single alternative for positioning and navigation
Among the most salient needs: higher quality (more expensive) oscillators for timing
“The most applicable mitigation strategies for the largest number of applications are eLoran and Satelles.”
“Omnisense and Locata may be preferred for localised applications that require high levels of accuracy.”
From the just-issued Blackett Report, the first figure displayed above presents recommended mitigations to impacts on GNSS applications in road, rail, maritime and aviation. Alternative options include composite or hybrid navigation, terrestrial radio systems, space weather forecasting, eLoran, various methods of interference detection, multi-frequency receivers and differential GNSS.
A second figure from Last’s presentation, shown above, covers the mitigations recommended for telecoms, finance, energy, and emergency services sectors. Mitigations for these applications include a resilient architecture with diverse network routing to high-stability atomic clocks, terrestrial radio systems, time-by-fiberoptics, multiconstellation receivers, holdover devices, GNSS integrity monitoring, and inertial navigation.
Concluding recommendations of the Blackett Report:
CNI operators to review and report on their reliance on GNSS. Cabinet Office to assess overall dependence of CNI on GNSS.
Add loss or compromise of GNSS-derived PNT to National Risk Assessment, not just as a dimension of space weather.
In allocating radio spectrum to new services and applications, address the risk of interference to GNSS-dependent users, including CNI.
Review the legality of the sale, ownership and use of devices and software to cause deliberate interference to GNSS receivers or signals.
Assess the need to monitor interference of GNSS at key sites such as ports and share the data with government
Employ GNSS-independent back-up systems.
Cross-government PNT Working Group to report to Cabinet Office on ways to improve national resilience.
Government to facilitate as those procuring GNSS equipment for CNI specify performance standards.
Map PNT testing facilities and explore how industry and critical services can better access them.
Leverage UK academic and industrial expertise in time and geo-location, increasing coordination among existing centres of excellence.
Korea will build its own navigation satellite system by 2034, providing independent positioning and navigation signals over an area spanning a 1,000-kilometer radius from the country’s capital, Seoul.
The Ministry of Science and information and communications technology (ICT) announced that it would finalize a plan for the Korean Positioning System (KPS) at a Space Committee meeting on Feb. 5.
According to a preliminary statement from the Ministry of Science and ICT, the KPS initiative will develop a ground test in 2021, core satellite navigation technology by 2022 and begin actual satellite production in 2024. The system will comprise a total of seven navigation satellites, three of them geostationary above the Korean Peninsula.
Figure from the 2016 paper shows a conceptual view of real-time WADGPS operation. The reference station transmits observation data at 1 Hz frequency to the master station. The master station is operated in real time and creates correction information and basic integrity information thereby configuring a message. A message is sent to the satellite communication simulation device according to its own transmission protocol. The satellite communication simulation device performs broadcasting of WADGPS correction information into the L1 band. A message created in every sec is coded with reserved GPS PRN C/A code and modulated with L1 frequency. Since additional correction information transmission medium such as geostationary orbit satellite or pseudolite is not considered in this study, radio frequency (RF) signals are created using simulation devices and performance was verified while connecting the signal with user receivers via cable. Additionally, a commercial communication network was used to transfer correction messages in order to verify user performance, which is located remotely. (Image: Korean Journal of Positioning, Navigation, and Timing)
Korea currently relies on the U.S. GPS system, which has suffered repeated local area jamming emanating from North Korea.
“As the GPS becomes a necessity in everyday life, broken signals for any reason can set off a nationwide chaos,” said an official for satellite navigation at the Korea Aerospace Research Institute (KARI).
Officials stated the the KPS will also improve available un-aided accuracy of GPS in its service area from about 10 meters now to less than one meter.
“Advanced nations are trying to secure strong GPS capabilities by sending up satellites to prevent a chaos that can take place while they depend on other nations’ satellites,” stated the KARI spokesperson.
The initiative appears to be separate from the Korean Wide Area Differential GPS System, whose development was the subject of a 2011 paper presented at the Institute of Navigation (ION) International Technical Meeting. The abstract for that paper stated:
“[The] project is scheduled for 2010 to 2014 under the contract with the Ministry of Land, Transport and Maritime affairs (MLTM). After that, Korea will launch a geostationary multifunctional satellite with a navigation payload which will be broadcasting augmenting signals for GPS.”
In March 2016, the Korean Journal of Positioning, Navigation, and Timing published a paper titled “Performance Analysis of WADGPS System for Improving Positioning Accuracy,” by Hyoungmin So , Jaegyu Jang, Kihoon Lee, unpyo Park and Kiwon Song. Its conclusion section stated:
“In this paper, configuration of observation reference stations and master station and initial experiment results were presented to verify accuracy correction performance of the WADGPS. The wide area correction algorithm was implemented using eight reference stations and one master station. For the initial performance verification, static and dynamic experiments were conducted. The experiment result showed that the static experiment had a horizontal accuracy performance with a level of 1 m (95 percent). In the dynamic experiment using a vehicle, performance degradation occurred compared to that of static experiment. The reason for this was due to the measured value error at the user receiver caused by multipath and visibility limitation. In summary, the implementation and performance of the algorithm of early stage were verified. For the future study, user operation characteristics will be considered and additional performance analysis on created correction information will be conducted.”
The U.S. Air Force is intermittently jamming its own GPS signals over southern Nevada and Utah this week and next as part of a massive air-to-air combat training exercise, Red Flag 18-1, based out of Nellis Air Force Base in Nevada. The jamming aims to challenge aircrews and their weaponry under realistic fighting conditions. The Air Force has warned that navigation systems including those found in commercial flights may be disrupted or jammed completely across the southwest U.S. during that time, ending February 16. So far no major commercial airline disruptions, flight delays or re-routings have been reported.
The U.S. military, heavily and perhaps overly reliant on GPS, is developing a range of position, navigation, and timing (PNT) technologies being to help overcome the loss of GPS during combat, an increasingly likely scenario now and in years to come. Some have speculated that this year’s exercise specifically has in mind a possible conflict on the Korean Penisula. GPS jamming has regularly emanated from North Korea over the past several years.
“We’re trying a few new and different things with Red Flag 18-1,” said Col Michael Mathes, 414th Combat Training Squadron commander. “This primarily is a strike package focused training venue that we integrate at a command and control level in support of joint task force operations. It’s a lot of words to say that we integrate every capability we can into strike operations that are flown out of Nellis Air Force Base.”
The exercise, which the Air Force conducts annually, typically involves a variety of attack, fighter and bomber aircraft with added participation from the U.S. Navy, U.S. Army, Marine Corps, Royal Australian Air Force and Royal Air Force. This year’s Red Flag is the largest in the exercise’s 42 year history.
Nellis Air Force Base in southern Nevada. (Image: USAF)
Affected Areas. “Arrivals and departures from airports within the Las Vegas area may be issued non-Rnav re-routes with the possibility of increased traffic disruption near LAS requiring airborne re-routes to the south and east of the affected area,” stated an Air Force bulletin. “Aircraft operating in Los Angeles (ZLA) center airspace may experience navigational disruption, including suspension of Descend-via and Climb-via procedures. Non-Rnav SIDs and STARs may be issued within ZLA airspace in the event of increased navigational disruption. Crews should expect the possibility of airborne mile-in-trail and departure mile-in-trail traffic management initiatives.”
Alternate Capabilities. Many Air Force planes have onboard inertial navigation systems, using accelerometers, gyroscopes, and magnetic sensors to continuously calculate position without GPS signal data, as well as at a higher hertz rate. When available, GPS signals can be used to correct inertial calculations, which tend to drift over time. Fighter planes can also use AESA-scanned array radars teamed with an inertial system for navigation over short ranges. Aircraft electro-optical and infrared sensors can also read terrain over short distances to provide additional navigation.
If strike aircraft have reliable communications or datalinks, other aircraft such as E-8 JSTARS, flying outside the GPS-disrupted zone, may be able to relay position and targeting information. Some missiles carried by strike aircraft have laser-guiding instead of or in addition to GPS-guiding.
The Japan-Australia QZSS Industrial Utilisation Workshop will be held Feb. 6 at the University of New South Wales (Kensington Campus), Room Chemical Sc M18, Sydney, Australia.
The workshop will share information about QZSS and GPS related technologies and the latest developments in the applications of this technology in a range of sectors including in agriculture, autonomous driving, advanced route guidance and the maritime sector.
The workshop will explore avenues for future cooperation with Australian organisations, both in the private and public sectors and report on trials undertaken in Australia using QZSS applications.
The QZSS Workshop will feature a range of keynote speakers from key Japanese Ministries including: the Ministry of the Economy and Industry (METI), the National Space Policy Secretariat (Cabinet Office), the Ministry of Internal Affairs and Communications (MIC) , Ministry of Agriculture, Forestry and Fisheries (MAFF) and Japanese industry, including Toyota Tsusho, Mitsubishi Electric (MELCO), Global Positioning Augmentation Service Corporation (GPAS), Hitachi Zosen Corporation (HITZ), as well as keynote speakers from the Australian public and private sectors.
