This month’s column deals with two troublesome topics: the U.S. government’s over-reliance on GPS, and the potential costs of GPS disruption toward which such a policy may be leading us.
First things first.
When someone utters the words “I’m nearly perfect,” get on your toes. Such self-appraisal usually masks something. It could be insecurity, denial, ignorance or simply fear. At the very least, some level of illusion, if not delusion, is involved.
The press release actually says, “The U.S. Air Force released two technical reports demonstrating that the Global Positioning System (GPS) continues to deliver exceptional performance to civilian users around the world….The 2014 and 2015 performance reports confirm that the GPS Standard Positioning Service (SPS) satisfied nearly all measurable performance commitments documented in the GPS SPS Performance Standard.”
Fair enough. Those are demonstrable facts. Nowhere does the release — other than in its headline — employ the words “perfect” or “near-perfect.”
The problem is, as current events repeatedly show, people remember only the headline. That may be all that they read or register in the first place.
Affixing the label “near-perfect” to GPS is “potentially dangerous,” points out Dana Goward of the Resilient PNT Foundation, “because it could exacerbate the public’s growing over-reliance on, and often blind faith in, GPS. Even if GPS did always perform perfectly, all kinds of things can happen to signals after they leave the satellites and before they get to receivers. Personal privacy devices, other jammers, spoofers, solar activity, other electromagnetic interference, even the local geography can significantly degrade or disable a receiver’s performance. That’s why in the GPS System Performance Standard the Air Force specifically says its responsibility ends once signals are in space.”
Perfection might exist in space, but it doesn’t down here.
Even in space, accidents sure will happen. The Air Force release documents GPS performance for 2014 and 2015. This conveniently draws up short of January 2016, when several GPS satellites broadcast a timing error that triggered equipment faults and failures globally for nearly 12 hours. Thus demonstrating something far from perfection.
Issuing a statement in the manner done on June 16 perpetuates a dangerous myth, keeps users in the dark about the actual state of affairs, cultivates a What-Me-Worry? approach to positioning, navigation and timing, and abets the lack of political will and understanding of GNSS vulnerabilities.
We have expanded the focus of this magazine to cover other technologies relevant and applicable to the field precisely because GPS, and by extension GNSS, great though they may be, are not perfect. Not even nearly.
At What Cost Ignorance?
A report recently compiled and released in the UK attempts to quantify the cost of a GNSS disruption, should one occur. The figure the authors came up with? 1 billion pounds sterling per day. That’s approximately $1,273,710,000.
Per day.
The report, available in either 11-page or 133-page versions, and titled The economic impact to the UK of a disruption to GNSS, looks at what would happen to the UK economy if GNSS were unavailable for five days. Five days is, indeed, a long time. One hopes that a fix could be obtained in less than that amount of time. But one never knows, does one?
“The economic impact to the UK of a five-day disruption to GNSS has been estimated at £5.2bn.” Thus the per diem figure above.
The report was commissioned by Innovate UK, the UK Space Agency and the Royal Institute of Navigation. It followed from the January 2016 accident referenced earlier, in which an error in the GPS signal from certain satellites, triggered by the decommissioning of one of those satellites, brought a number of key industrial servers to their knees. The episode lasted 12 hours.
This report hypothesizes a more fleshed-out disaster and estimates the likely impact of a disruption to GNSS availability for up to five days across ten application domains in the UK: Road, Rail, Aviation, Maritime, Food, Emergency and Justice Services, Surveying, Location-Based Services (LBS), Other Infrastructure, and Other Applications.
The report is worth reading, not only for its figures, methodology, and discussion of mitigation, but also for two salient pages: “A day in the UK with GNSS” and “A day in the UK without GNSS.” At home, on the move, with others, at work, at the shops, when things go wrong, back at home. A post-modern (or post-Beatles) “Day in the Life.”
Even if the hypothetical disruption were not to last 5 days, but a much shorter period, perusing the two chronologies of with and without can serve to remind us how many of our daily activities are keyed to and thus dependent on GPS/GNSS.
Having no viable, working back-up — not even on the visible horizon — to such an essential system makes sense how?
The second set of 10 Iridium NEXT satellites, launched June 25 by SpaceX, are functioning nominally and have begun the testing and validation process.
The batch of 10 satellites was launched from Vandenberg Air Force Base in California, increasing the total number of Iridium NEXT satellites in space to 20.
“We are thrilled with yesterday’s success,” said Scott Smith, chief operating officer at Iridium. “These new satellites are functioning well, and we are pressing forward with the testing process.”
“Since the last launch, the team at our Satellite Network Operations Center has been anxiously awaiting this new batch of satellites. There is a lot of work to do, and we are up for the challenge,” he said.
Now, and for approximately the next 45 days, the newly launched satellites will undergo a series of testing and validation procedures, ensuring they are ready for integration with the operational constellation.
Once testing is completed, Iridium will also hand over control of Aireon’s Automatic Dependent Surveillance-Broadcast hosted payload, to the team at Aireon’s Hosted Payload Operations Center, in Leesburg, Virginia.
The Trimble VRS Now GNSS correction service is now available in France. The service is designed for a variety of geospatial and construction applications including surveying, cadastral, land administration, and urban and rural construction that would benefit from easy access to high-accuracy, centimeter-level positioning.
Trimble also now provides Galileo support for VRS Now. Powered by the Trimble Pivot Platform, VRS Now in Europe fully supports GPS, GLONASS, BeiDou, QZSS and the Galileo satellite system.
Galileo support improves network performance and reliability with access to additional satellites, particularly in urban canyons or other harsh environments. The increased number of visible satellites provides additional data observations that enhance positioning integrity to better mitigate errors.
“Trimble continues to aggressively expand its VRS Now footprint in Europe,” said Patricia Boothe, general manager of Trimble’s Advanced Positioning Division. “With the addition of correction services in France, Trimble VRS Now covers over 179 million square kilometers (732 million square miles) across 10 countries.”
VRS Now coverage is available throughout the majority of France as well as Belgium, The Czech Republic, Estonia, Germany, Great Britain, Ireland, Luxembourg, the Netherlands and Sweden using a compatible GNSS receiver or display.
Subscriptions are available through Trimble’s Authorized Business Partners or Trimble’s online store.
In a specialized cleanroom designed to streamline satellite production, Lockheed Martin is in full production building GPS III — the world’s most powerful GPS satellite, according to the company. The company’s second GPS III satellite is now assembled and preparing for environmental testing, and the third satellite is close behind, having just received its navigation payload.
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.
In May, 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. GPS III SV02 smoothly came together through a series of carefully-orchestrated manufacturing maneuvers utilizing a 10-ton crane.
GPS III SV02 is part of the Air Force’s next generation of GPS satellites, which have three times better accuracy and up to eight times improved anti-jamming capabilities. Spacecraft life will extend to 15 years, 25 percent longer than the newest GPS satellites on-orbit today.
“Now fully-integrated, GPS III SV02 will begin environmental testing this summer to ensure the satellite is ready for the rigors of space,” said Mark Stewart, vice president of Navigation Systems for Lockheed Martin. “This testing simulates harsh launch and space environments the satellite will endure, and further reduces any risk prior to it being available for launch in 2018.”
A Factory Full of GPS III Satellites
Right behind GPS III SV02, eight more contracted GPS III satellites are moving through production flow at Lockheed Martin’s nearly 40,000 sq. ft., state-of-the-art GPS III Processing Facility near Denver.
GPS III SV03 recently completed initial power on of its bus, which contains the electronics that operate the satellite. The company received SV03’s navigation payload from its supplier, Harris Corporation, in May. After further system testing, SV03 will be ready for full integration later this fall.
GPS III SV04’s major electronics are being populated as it prepares for its own initial power on. This satellite’s navigation payload is expected to arrive and be integrated into its space vehicle before the end of the year.
Right behind the second GPS III space vehicle (GPS III SV02), eight more contracted GPS III satellites are moving through production flow at Lockheed Martin’s nearly 40,000 sq. ft., state-of-the-art GPS III Processing Facility (GPF) near Denver.
Components of the next six satellites, GPS III SV05-10, are arriving at Lockheed Martin daily from more than 250 suppliers in 29 states. To date, more than 70 percent of parts and materials for SV05-08 have been received. The company was put under production contract for SV09-10 in late 2016.
All of these satellites are now following the Air Force’s first GPS III satellite, GPS III SV01, through a proven assembly, integration and test flow. SV01 completed its final Factory Functional Qualification Testing and was placed into storage in February 2017 ahead of its expected 2018 launch.
Investing in the Future of GPS III
With multiple satellites now in production, Lockheed Martin engineers are building GPS III smarter and faster. Key to their success is the company’s GPS III Processing Facility, a cleanroom manufacturing center designed in a virtual-reality environment to maximize production efficiency. Lockheed Martin invested $128 million in the new center, which opened in 2011.
The company’s unique satellite design includes a flexible, modular architecture that allows for the easy insertion of new technology as it becomes available in the future or if the Air Force’s mission needs change. Satellites based off this design also will already be compatible with both the Air Force’s next generation Operational Control System (OCX) and the existing GPS constellation.
“From day one, GPS III has been a team effort and our successes would not have been possible without a strong Air Force partnership,” Stewart said. “GPS III will ensure the U.S. maintains the gold standard for positioning, navigation and timing. We look forward to bringing GPS III’s new capabilities to our warfighters and beginning to launch these satellites in 2018.”
The GPS III team is led by the Global Positioning Systems Directorate at the U.S. Air Force Space and Missile Systems Center. Air Force Space Command’s 2nd Space Operations Squadron (2SOPS), based at Schriever Air Force Base, Colorado, manages and operates the GPS constellation for both civil and military users.
UK’s SSTL to build third batch of Galileo navigation payloads
News from the European Space Agency
Europe’s Galileo navigation constellation will gain an additional eight satellites, bringing it to completion, thanks to a contract signed at the Paris Air and Space Show.
The contract to build and test another eight Galileo satellites was awarded to a consortium led by prime contractor OHB, with Surrey Satellite Technology Ltd overseeing their navigation platforms.
This is the third such satellite signing: the first four In Orbit Validation satellites were built by a consortium led by Airbus Defence and Space, while production of the next 22 Full Operational Capability (FOC) satellites was led by OHB.
These new batch satellites are based on the already qualified design of the previous Galileo FOC satellites, except for changes on the unit level – such as improvements based on lessons learned and reacting to obsolescence of parts.
ESA’s Director of the Galileo Programme and Navigation-related Activities, Paul Verhoef, signed the contract with the CEO of OHB, Marco Fuchs and OHB Navigation Director Wolfgang Paetsch, in the presence of ESA Director General Jan Woerner and the EC’s Deputy Director-General for Internal Market, Industry, Entrepreneurship and SMEs, Pierre Delsaux.
“This procurement from OHB will enable the completion of the Galileo constellation and have reserves both in-orbit and on-ground,” said Director Verhoef. “This signing delivers the necessary infrastructure robustness that is essential for the provision of Galileo services worldwide.”
ESA signed the contract on behalf of the EU represented by the European Commission – Galileo’s owner. The Commission and ESA have a delegation agreement by which ESA acts as design and procurement agent on behalf of the Commission.
Signing Ceremony
Galileo is Europe’s own satellite navigation system, providing an array of positioning, navigation and timing services to Europe and the world.
With 18 satellites now in orbit, Galileo began Initial Services on Dec. 15, 2016, the first step towards full operational capability.
Further launches will continue to build the satellite constellation, which will gradually improve the system performance and availability worldwide. The launch by Ariane 5 of another four satellites is due to take place later this year.
The full Galileo constellation will consist of 24 operational satellites in three orbital planes plus orbital spares, intended to prevent any interruption in service.
These new eight satellites will provide the constellation with in-orbit and on-ground spares. ESA and the Commission are also in the process of developing an improved Galileo Second Generation for the next decade.
Galileo is now providing three service types, the availability of which will continue to be improved.
ESA’s Director of the Galileo Programme and Navigation-related Activities, Paul Verhoef (right), signing the contract of behalf of the European Commission, shakes hands with the CEO of OHB, Marco Fuchs beside OHB Navigation Director Wolfgang Paetsch, in the presence of ESA Director General Jan Woerner (in background) and the EC’s Deputy Director-General for Internal Market, Industry, Entrepreneurship and SMEs, Pierre Delsaux.
Galileo coverage
The Open Service is a free mass-market service for users with enabled chipsets in, for instance, smartphones and car navigation systems. Fully interoperable with GPS, combined coverage will deliver more accurate and reliable positioning for users.
Galileo’s Public Regulated Service is an encrypted, robust service for government-authorized users such as civil protection, fire brigades and the police.
The Search and Rescue Service is Europe’s contribution to the long-running Cospas–Sarsat international emergency beacon location. The time between someone locating a distress beacon when lost at sea or in the wilderness will be reduced from up to three hours to just 10 minutes, with its location determined to within 5 km, rather than the previous 10 km.
The public will begin benefiting as Galileo-capable devices enter the marketplace: 17 companies, representing more than 95% of global supply, now produce Galileo-ready chips.
SSTL continues Galileo work
“SSTL is delighted to have been selected to build the third batch of navigation payloads needed to complete the initial Galileo Constellation,” said Gary Lay, SSTL’s director of navigation. “I am confident that the OHB-SSTL solution offered the lowest risk and best value for money, and I believe that our selection as payload providers for the third time in succession demonstrates a high regard for our work.”
SSTL’s state-of-the-art Galileo FOC payload comprises different units including European sourced atomic clocks, navigation signal generators, high power traveling wave tube amplifiers and antennas. SSTL’s payload proposal for Batch 3 is for a recurrent build of the existing payload, with an evolution of the atomic clocks to incorporate advances made under the European GNSS Evolution Programme.
Fourteen of SSTL’s Galileo FOC navigation payloads are currently operational in orbit, with a further eight payloads already delivered to OHB for integration and test.
SSTL has been involved in the Galileo program since 2003 with the design and build of GIOVE-A, Galileo’s pathfinder mission. GIOVE-A was launched in 2005 and is still operational today, providing valuable data about the radiation environment in Medium Earth Orbit. An experimental GPS receiver on board GIOVE-A is also used to map out the antenna patterns of GPS satellites for use in planning navigation systems for future high altitude missions in Geostationary orbit, and beyond into deep space.
It’s been a few months since I’ve published a GSS Monthly newsletter column. What a busy few months it has been. It’s been all about UAVs, high-precision GNSS projects and GIS, with some conferences and workshops sprinkled in between. High-accuracy GNSS technology and UAV technology are hot trends— red hot.
UAVs: Prosumer and mapping on a slope
Obviously, consumer UAVs have exploded in the mainstream consumer electronics market during the past five years. Since the FAA began requiring UAVs to be registered in late 2015, far more UAVs have been registered (~700,000 to date) with the FAA than manned aircraft (~320,000).
In fact, the number of registered UAVs aircraft eclipsed registered manned aircraft more than a year ago! The FAA reported that at any one point during the day, there are ~7,000 manned aircraft flying in the U.S. airspace. That begs the question, how many UAVs are flying above our heads at any one point in time? No one can answer that question.
On the coattails of consumer UAVs in mainstream America is the use of UAVs in the USA’s commercial world. Since the FAA opened the floodgates in August 2016 to allow almost anyone to fly UAVs for business ($150 and answer 42 out of 60 questions correctly), lots and lots of companies are buying inexpensive “prosumer” UAVs and extracting tremendous value from them.
Prosumer electronics is equipment and software targeted at the consumer market but also good enough to be used for business. The UAV market is a perfect example of this. DJI, by far the biggest UAV manufacturer in the world at $1B+ in annual revenue, targets the mainstream consumer market and sells a huge number of low-, medium- and high-end UAVs to businesses. Think about it: You can buy a DJI Phantom 4 Pro at your local Apple Store and the next day be generating one-foot elevation contours on a project site!
Following is an example of a papermill I flew a few weeks ago. I flew it in less than one hour (50 acres), generated an orthophoto with 2.4-cm/pixel resolution and a digital elevation model (DEM) with 4.79-cm/pixel resolution.
Figure 1. 2.4-cm/pixel resolution orthophoto, 50 acres.Figure 2. DEM with 4.79-cm/pixel resolution of the same flight.Figure 3. Zoomed-in image of the same DEM.
The detailed data above, generated from a $1,500 UAV, is clearly outstanding. By the way, the purpose of the project was to determine the volume of the various stockpiles, which I’ve not computed yet. But if the volume calcs are close enough to the traditional terrestrial-based measuring methods, the UAV return on investment (ROI) argument will be hard to beat.
It takes ~14 hours each month to measure all the stockpiles on this site using traditional terrestrial measurement tools. Also, the measurements must be taken on the weekend when the site activity is minimal. It took less than one hour to fly the entire site, and I flew it twice (one time west-east direction at 80/80 overlap and one time north-south at 70/70 overlap) to make sure I had enough data. I mean, seriously, I drove 1.5 hours to the site. Why not spend another 20 minutes to fly it in a perpendicular direction?
To date, I’ve only flown relatively flat sites such as construction sites, agricultural fields, and industrial sites. That was until a couple of weeks ago. While I’ve become pretty comfortable at flying open and relatively flat sites over the past 18 months, I’ve not ventured into flying a site with a lot of elevation changes and tree canopy. I finally did that earlier this month, and it was both challenging and rewarding. There are a few problems on sites with major elevation changes and tall tree canopy:
A. Maintaining visual line of sight (VLOS) as required by the FAA.
B. Flying in such a manner that the image-processing software has good quality data to work with so you can generate the products you need.
The mission planning/control software plays a very important roll in this process. Well, it always does, but it really does in this case. Typically, the mission planning/control folks want you to fly at a consistent height above the ground so your overlap is consistent. This is very difficult to accomplish if you’re flying a site with a lot of elevation change. In that case, they typically tell you to launch from the highest (or nearly the highest) elevation point and fly at that elevation.
The problem this causes is that you could end up flying 500, 600 or 700 feet above ground level (AGL). For example, if you are flying a site with 500 feet of elevation change and you instruct the mission planning/control software to fly at 350 feet AGL, at some point in the project the UAV will be at 850 feet AGL. That can be a problem from both a regulatory standpoint (FAA allows UAV flights up to 400 feet AGL) and an image-processing standpoint.
Fortunately, the mission planning/control software I use just introduced a Terrain Awareness feature. It uses SRTM (Shuttle Radar Topography Mission) elevation data. Granted, it’s 30-meter pixel elevation data, so each elevation block is 30 meters x 30 meters, so I really wondered if the resolution was high enough. The site I was going to fly was only 60 acres in size and had 550 feet of elevation change. Note that the trees on the site had already been harvested, so the land was relatively clear. There’s about a 550-foot difference from the projected launch point (purple dot) to the northern and western end of the site. Following is the mission plan for the site I was planning to fly.
Figure 4. 60-acre site with ~550 feet of elevation change.
To give you an idea of the slope, the solid red lines in the following image are 100-foot elevation contour lines. The green triangle is the projected UAV launch point. This was a great launch point because I could see the entire site and maintain VLOS.
Figure 5. Site topo with projected UAV launch point.
I chose to fly the mission at 300 feet AGL. I figured it would be high enough if there was some “slop” in the SRTM elevation model. Still, I was concerned about the resolution of the SRTM data because at 300 feet AGL, my UAV would be flying below the launch elevation due to the extreme elevation slope on the site. Remember, the Terrain Awareness feature of the mission planning/control software is based on the SRTM elevation data, and not based on any sensors in the UAV itself — if the SRTM elevation data was incorrect, my UAV might crash into the ground.
Following is the SRTM elevation data along with the flight path data displayed in the mission planning/control software.
Figure 6. The projected UAV flight path based on the SRTM elevation data.
The moment of truth came when I launched the UAV from the start point (purple dot) and watched it rise to 300 feet AGL to start its mission. The first few swaths were uneventful. After that, it started to fly into the canyon, following the terrain as programmed, then rise up from the canyon during each pass. It was a thing of beauty to watch.
Unfortunately, about 70% of the way through the mission, it started raining, so we called it quits. However, we proved that at least on the four sites I flew that day, the SRTM data and Terrain Awareness feature were effective in collecting data in steep-slope environments. Following is the 2.69-cm/pixel orthophoto generated from the flight. Note the tracks where the logging rigs pulled the logs up the steep slope.
Figure 7. 2.69-cm/pixel resolution orthophoto.
Following is a zoomed-in view of the UAV launch site.
Figure 8. Zoomed-in view of the orthophoto.
Following is an image of the 5.37-cm/pixel DEM generated from the flight data. Notice the logging tracks.
Figure 9. 5.7-cm/pixel image of the DEM generated from the flight data.
Following is a zoomed in view of the 5.37-cm/pixel DEM image.
Figure 10. Zoomed-in 5.37-cm DEM image of UAV launch point.
The mission was successful in proving that SRTM elevation data was sufficient enough to fly a mission with a dynamic AGL. It handled the steep slopes by maintaining a sufficient AGL elevation as I hoped it would despite only having 30-meter x 30-meter block elevation resolution. The image processing software seemed to like the UAV data, as you can see from the results above. I didn’t have to spend any additional processing time over and above what I usually spend in order to generate these products.
I did experience a hiccup with the mission planning/control software running on my iPad Mini 2. It turns out that the Terrain Awareness feature in my mission planning/control software requires some extra CPU horsepower — the software overpowered my iPad Mini and crashed once during a mission. The UAV kept flying its intended course as instructed, but it stopped taking photos when the software crashed, so I brought it back to the launch point.
After visiting the software vendor’s website, it became clear to me that it’s probably time to upgrade my iPad Mini to the latest model to keep up with the new features being implemented in the software.
A Quick Note on High-Accuracy GNSS
In March, I attended the Hawaii GIS conference and decided to perform some benchmark testing on a survey mark using WAAS and a high-accuracy GNSS receiver.
My goal was two-fold.
See how WAAS is behaving in Hawaii. WAAS in Hawaii is an anomaly because it’s far away from the Continental U.S. (CONUS) where all the WAAS reference stations are located (there’s one in Honolulu, but that’s it). In other words, Hawaii is the most challenging place for WAAS accuracy in North America.
See how many GNSS satellites I could track and use in Hawaii.
Holy moly, was I surprised at how good it was. I’ve tested WAAS in Hawaii several times in the past many years. The last time I tested it was in 2013 and the GNSS receiver I used (GPS + GLONASS) achieved a steady 80-cm accuracy. That was pretty darned good for WAAS in Hawaii at that time.
I packed up some receivers and hiked about 4 miles to a survey mark I could find in Honolulu. I was a great survey mark for testing because it was on the sidewalk of a quiet residential street. Following is a photo of the survey mark.
Figure 11. PID DK4162 survey mark in Honolulu.
I set up on the survey mark and then looked at the satellites the receiver was tracking. I wanted to know how many GPS, GLONASS, Galileo and BeiDou satellites were being used. Following is a screen shot.
Figure 12. Total number of GNSS satellites being used – 23.
Twenty-three GNSS satellites being used! Are you kidding me? This is more than double the number of GPS satellites being used. This illustrates the power of four-constellation GNSS that is only going to continue to get better over the next several years.
What surprised me the most was the number of Galileo satellites being used, and this was before two Galileo satellites were declared healthy in late May.
My next test was to evaluate WAAS accuracy. Who cares how many satellites the receiver is using if the accuracy isn’t improved? I plumbed the receiver antenna on the survey mark and plotted ~7 minutes of data.
Figure 13. Accuracy plot compared to the DK4162 survey mark coordinates.
Yep, that’s about 30-cm accuracy over a 7-minute period. That’s better by a factor of two compared to the accuracy I saw in 2013. Sure, WAAS has improved somewhat, and maybe the ionosphere was particularly happy that day, but I have to believe that the additional GNSS satellites contributed the most to the improvement in accuracy. In the next few months, I’m going to be performing more tests with WAAS and RTK on my GNSS test course near my office. I’ll keep you posted on the results of those tests.
The Esri International User Conference – July 10-14
As usual, I’ll be attending the largest gathering of GIS professionals in the U.S. next month, the Esri International User Conference. 16,000 of our colleagues will descend upon San Diego to share, network and enjoy the spatialness that we have for one another.
If you’re interested, I’m giving a couple of presentations at the Esri UC:
Tuesday (July 11), 08:30 a.m., Room 28B (subject to change)
Paper Title: An Efficient, Accuracy Mobile GIS Workflow using RTK GNSS
Session Title: Mobile Data Collection
This is cool project I worked on with WaterOne, a large water utility, to design a real-time, high-accuracy GNSS workflow in the Esri environment. They are collecting data at the centimeter level for mapping their above-ground assets as well as new construction using tablet computers and RTK GNSS receivers.
Thursday (July 13), 8:30 a.m., Room 29C (subject to change)
Paper Title: UAV (drone) applications for water utilities
Session Title: Applied GIS: Three Unique Examples
This is some groundbreaking work I’ve done with American Water on using UAV technology for mapping and inspection. We did a lot of experimenting during the proof-of-concept phase to figure out what applications are practical and which aren’t.
The Springer Handbook of Global Navigation Satellite Systems is now available.
Described as “A state-of-the-art description of GNSS as a key technology for science and society at large,” the 1,327-page tome is edited by Peter J.G. Teunissen and Oliver Montenbruck.
Teunissen is a professor of Geodesy and Satellite Navigation at Curtin University, Australia, and Delft University of Technology (TU Delft), the Netherlands.
Montenbruck is head of the GNSS Technology and Navigation Group at the DLR’s German Space Operations Center, Oberpfaffenhofen, and chair of the Multi-GNSS Working Group of the International GNSS Service, as well as being a GPS Worldcontributor and recipient of the GPS World Leadership Award.
Exhaustive Reference. The handbook presents a complete and rigorous overview of the fundamentals, methods and applications of the multidisciplinary field of GNSS, providing an exhaustive, one-stop reference work and a state-of-the-art description of GNSS as a key technology for science and society at large.
All global and regional satellite navigation systems, in operation and under development (GPS, GLONASS, Galileo, BeiDou, QZSS, IRNSS/NAVIC, SBAS), are examined in detail. The functional principles of receivers and antennas, as well as the advanced algorithms and models for GNSS parameter estimation, are rigorously discussed.
The book covers the broad and diverse range of land, marine, air and space applications, from everyday GNSS to high-precision scientific applications and provides detailed descriptions of the most widely used GNSS format standards, covering receiver formats as well as IGS product and meta-data formats.
The full coverage of the field of GNSS is presented in seven parts, from its fundamentals, through the treatment of global and regional navigation satellite systems, of receivers and antennas, and of algorithms and models, up to the broad and diverse range of applications in the areas of positioning and navigation, surveying, geodesy and geodynamics, and remote sensing and timing.
Each chapter is written by international experts and amply illustrated with figures and photographs, making the book an invaluable resource for scientists, engineers, students and institutions alike.
The U.S. Air Force released two technical reports demonstrating that the Global Positioning System (GPS) continues to deliver exceptional performance to civilian users around the world, reported the Los Angeles Air Force Base.
Operated by the 50th Space Wing at Schriever Air Force Base, Colorado, the GPS constellation provides precise PNT services worldwide 24-hours a day, seven days a week.
The 2014 and 2015 performance reports confirm that the GPS Standard Positioning Service (SPS) satisfied nearly all measurable performance commitments documented in the GPS SPS Performance Standard, furthering the status of GPS as the “Gold Standard” for PNT.
The GPS Directorate at the U.S. Air Force’s Space and Missile Systems Center commissioned the GPS SPS performance reports to enhance public transparency of the real-world performance of civil GPS.
The GPS Directorate at the U.S. Air Force’s Space and Missile Systems Center commissioned the GPS SPS performance reports to enhance public transparency of the real-world performance of civil GPS. The reports confirm that GPS met all of the evaluated commitments for calendar years 2014 and 2015 with one exception.
This exception was that the reporting notification commitment for scheduled GPS satellite interruptions during calendar year 2014 was only met in 29 of 30 cases (96.7 percent). The vast majority of GPS users were not impacted by this single delayed notification. In this single case, the U.S. Air Force only provided 17 hours of advanced notice, as opposed to the SPS PS commitment of at least 48 hours advanced notice, before the scheduled satellite interruption.
The commitments evaluated in the reports include those of accuracy, integrity, continuity, and availability of the GPS signals-in-space. For example, the signal-in-space ranging accuracy of the GPS civil signals was significantly better than the published standard of “7.8 meters or better at the 95th percentile.” This metric represents a key component in the total “user range error” that GPS receivers experience.
Most impressively, the oldest GPS satellites still provided an average signal-in-space accuracy of 2.8 meters during their worst performing month of 2015 – surpassing the target accuracy metric by over 300 percent. On average, the signal-in-space accuracy of the GPS constellation in 2015 was 1.4 meters, which is a 0.4 meter improvement over the accuracy in 2013.
The GPS SPS performance reports are generated by Applied Research Laboratories, the University of Texas at Austin (ARL:UT), which is a Department of Defense University-Affiliated Research Center. Using data from 33 GPS monitoring and reference stations located around the globe, the ARL:UT team assesses GPS performance against the commitments defined in the 2008 GPS SPS Performance Standard. The ARL:UT reports focus on those commitments that can be verified by anyone with knowledge of standard GPS data analysis practices, familiarity with the relevant signal specifications, and access to a Global Navigation Satellite System data archive.
“The GPS Directorate remains committed to providing highly accurate and reliable PNT services to our users around the globe. The use of published standards to transparently guide data-driven decision making is how we have become the ‘Gold Standard’ in PNT,” said Col. Steven Whitney, director of the GPS Directorate. “The GPS Directorate is working every day on improved capabilities to ensure users receive the maximum benefit of the PNT services offered by GPS.”
ARL-UT expects to complete the 2016 SPS performance report later this year. The 2013, 2014 and 2015 reports are publicly available for free download. The National Coordination Office for Space-Based PNT maintains the GPS.gov website to provide official information about GPS to the public.
Air Force Space Command’s Space and Missile Systems Center, located at Los Angeles Air Force Base in El Segundo, California, is the U.S. Air Force’s center of excellence for acquiring and developing military space systems. Its portfolio includes GPS, military satellite communications, defense meteorological satellites, space launch and range systems, satellite control networks, space-based infrared systems and space situational awareness capabilities.
The invisible signals that Europe’s Galileo satellites are beaming down to the world are officially award-winning: the team behind their design has won the European Inventor Award, run by the European Patent Office, reports the European Space Agency.
Just like the Galileo satellites and their globe-spanning ground stations, the Galileo signals themselves needed to be designed, having to pack multiple Galileo services aimed at different classes of users within the limited frequency bands allocated for the system by the International Telecommunications Union.
This task was accomplished by the Galileo Signal Task Force, a multinational group of experts who came up with a pair of innovative signal modulation techniques.
This team was led by Spanish engineer José Ángel Ávila Rodríguez – now part of ESA’s Galileo team – and his French colleague Laurent Lestarquit from France’s CNES space agency, sharing in the European Patent Office’s European Inventor Award 2017.
The team also includes German Günter Hein, formerly head of the department studying the evolution of EGNOS and Galileo for ESA, as well as Belgian Engineer Lionel Ries, now in ESA’s technical directorate, as well as French CNES engineer Jean-Luc Issler.
“When the nations of Europe work together, the whole world benefits,” said José.
With 18 satellites now in orbit, Galileo began Initial Services on 15 December 2016, so the two signals the team devised are now everyday reality.
They took as their inspiration the GPS system, with signal shapes first designed back in the 1960s, but first fulfilling user needs today.
The first signal technique is called Alternative Binary Offset Carrier modulation, or ‘AltBOC’ for short, combining four separate signals into one large ones – resulting in the largest bandwidth navigation signal ever transmitted.
When used in its full performance AltBOC can support precision scientific applications such as geodetic measurements and seismic monitoring.
The second modulation method, called Composite Binary Offset Carrier or ‘CBOC’, results in a signal for use by the mass market, possessing both narrowband and wideband components.
The result is a signal that can work well with low-end receivers – such as those found in current smartphones – while the wideband component ‘future proofs’ the signal, allowing manufacturers to extend mass market receiver performance in the future.
The other goal CBOC had to match was to be interoperable with GPS signals, allowing receivers to use both sets of signals at once on a seamless basis.
With China planning to use a comparable CBOC-style solution for their Beidou satnav satellites, the resulting Galileo E1 Open Signal is set to become the new standard for mass market applications for the foreseeable future.
Spirent Communications’ testing systems are being used by the European Union TREASURE project (Training, REsearch and Applications network to Support the Ultimate Real-time high-accuracy EGNSS).
The aim of the four-year project is to provide instantaneous and high-accuracy positioning anywhere in the world, exploiting different satellite systems operating together to provide users with positional accuracy of a few centimeters.
Spirent’s GSS7000 test system.
By 2020 Galileo, the European GNSS system (EGNSS), will be fully operational and provide positioning data of unprecedented accuracy. Galileo’s integration with other satellite systems through the TREASURE project is key to increasing Europe’s competitiveness in the field, which has been mainly based on the GPS system in the past 20 years.
Higher accuracy services will not only assist safety-critical industries such as air and maritime navigation services, but also help industries such as the global agri-tech market, autonomous vehicles and capital-intensive sectors.
Kimon Voutsis, Robust PNT Solutions Architect, works on a professional services project for a client.
For example, more accurate real-time positioning data can assist farmers in maximizing food production, reducing costs and minimizing the environmental impact. Equally, a deep-sea drilling platform that experiences any temporary degradation in positioning accuracy could lead to significant financial losses.
“Spirent is proud to support multi-national initiatives that advance our industry and provide better end user performance,” said Martin Foulger, general manager of Spirent’s positioning business unit. “More systems are using GNSS data, and users always want better accuracy, so TREASURE will help to provide this.”
TREASURE is an EU-funded project under the H2020-Marie Skłodowska-Curie Innovative Training Network. It is coordinated by the University of Nottingham, and Spirent is the partner providing GNSS simulation systems.
For more information on Spirent’s GNSS testing solutions, visit the website. To learn more about how to test receivers of GPS, Galileo and other GNSS, download Spirent’s eBook.
To learn more about TREASURE, contact Marcio Aquino, Nottingham Geospatial Institute.
The European Space Agency (ESA) has signed a contract with Thales Alenia Space for an upgrade to Europe’s EGNOS satellite navigation augmentation system, which underpins the safety-critical use of satnav across Europe, according to ESA.
Designed by ESA and being exploited by Europe’s GNSS Agency (GSA), the European Geostationary Navigation Overlay Service (EGNOS) improves the precision of GPS signals over most European territory, while also providing continuous and reliable updates on the “integrity” of these GPS signals.
A network of ground monitoring stations throughout Europe performs an independent measurement of GPS signals, so that corrections can be calculated, and then passed to users immediately via a trio of geostationary satellites.
The result is that the EGNOS-augmented signals are guaranteed to meet the extremely high performance standards set out by the International Civil Aviation Organisation standard, adapted for Europe by Eurocontrol, the European Organisation for the Safety of Air Navigation.
Paul Verhoef, ESA director of the Galileo Program, and Philippe Blatt, VP Thales Alenia Space France, sign on June 6 a contract for an upgrade of EGNOS.
Paul Verhoef, ESA’s director of the Galileo programme and navigation-related activities, signed the contract at ESA Headquarters in Paris with Philippe Blatt, vice president of Thales Alenia Space France.
ESA is performing the procurement of EGNOS Version 2.4.2 under the overall program authority of the GSA, which oversees both EGNOS and Europe’s Galileo satellite navigation system.
Two upgraded EGNOS releases will be provided over the course of the development: EGNOS V2.4.2I and EGNOS V2.4.2A.
The releases will resolve various obsolescence issues related to EGNOS’s central processing facility, based in Toulouse, France — which generates the corrections and integrity information to be broadcast across the European continent — to ensure continuity of EGNOS services into the future, including safety-of-life services, to an ever-expanding community of users.
The new contract includes:
a refreshment and enhancement of the Central Processing Facility design without algorithm modification
an optimized qualification process
a guarantee of full compliance to safety-critical software development requirements
the performance of end-to-end verification activities extending to the three geostationary satellites used by the system
ensuring compliance to a new set of technical requirements and international standards.
Editor’s Note: This online preview presents brief highlights from the upcoming July cover story in GPS World, “Navigation from LEO: Current Capability and Future Promise.” The article is by David Lawrence, H. Stewart Cobb, Greg Gutt, and Michael O’Connor of Satelles, Tyler G. R. Reid and Todd F. Walter of Stanford University, and David Whelan.
Robust position, navigation, and timing services from low Earth orbit (LEO) are here today, providing augmentation to GPS where GPS isn’t available. The addition of navigation signals from LEO provides a number of benefits. The proximity of LEO satellites has the potential to provide much stronger signals than the distant GNSS core-constellations like GPS in medium-Earth orbit (MEO).
Today, the only LEO system with global coverage is the Iridium constellation used primarily for communications.
Figure 1 shows the 31-satellite GPS constellation in contrast with the 66-satellite Iridium network. The scale of the difference in distance (several Earth radii) is extraordinary. The result is that Iridium signals are 300 to 2400 times stronger than GNSS signals on the ground, making them attractive for use in position, navigation, and timing (PNT) applications where GNSS signals are obstructed.
Figure 1. The 66 satellite Iridium constellation in low Earth orbit and 31 satellite GPS constellation in medium Earth orbit.
LEO-based PNT is now mainstream, in the form of real-time signals that have been delivered over the Iridium satellite network since May 2016. This service is made possible by Satelles in partnership with Iridium Communications Inc. in a service called the Satellite Time and Location (STL), a non-GNSS solution for assured time and location that is highly resilient and physically secure. Consumers, businesses, and governments are already using these LEO-based signals in environments with high GNSS interference or occlusion.
The security features of these signals are also used to reliably validate GNSS position, navigation and time (PNT) solutions in real time to help mitigate potential spoofing. Furthermore, the fast LEO orbits of Iridium generate Doppler-frequency signatures significantly stronger than GPS, increasing the utility of the STL signal for positioning applications.
STL field tests demonstrate a positioning accuracy of 20 meters and timekeeping to within 1 microsecond, all in deep attenuation environments indoors. This adds substantial robustness in augmenting the GNSS core-constellations like GPS and also allows for a standalone backup in many applications.
Along with its strong signals compared to the GNSS core-constellations in MEO, Iridium’s global coverage makes it ideal for use in PNT applications where GNSS is obstructed. Figure 1 shows the scale of the difference in altitude with Iridium at 780 kilometers and GPS at 20,200 kilometers. This has substantial implications not only for signal strength but also for coverage.
Though Iridium has twice as many satellites as GPS, at the equator users can often only see one satellite whereas they can see ten from GPS. This was one of the fundamental trades considered in the design of the GPS constellation. The higher the altitude, the more each launch cost; the lower, the more satellites had to be built to provide coverage. To put this in perspective, global coverage for one satellite in view at all times requires fewer than ten satellites in MEO but requires closer to one hundred in LEO.
Future LEO Constellations
The hundreds of LEO satellites needed to match the coverage of GPS may be coming. In late 2014 and early 2015, the International Telecommunication Union (ITU) reported a half dozen filings for spectrum allocation for large constellations of LEO satellites.
In January 2015, OneWeb announced a partnership with Virgin and Qualcomm to produce a constellation of 648 LEO satellites to deliver broadband Internet globally. This represents the next order of magnitude, with tenfold more satellites than Iridium. Within days of this announcement, SpaceX, with support from Google, announced a similar ambition for a constellation of more than 4,000 LEO satellites.
In August 2015, Samsung expressed interest in a proposal for a LEO constellation of 4,600. Boeing joined the race in June 2016 announcing plans for a LEO constellation of nearly 3,000 satellites. These LEO constellations are being proposed to keep up with the rising demand for broadband, not to replace ground infrastructure.
LEO versus MEO
Low- and medium-Earth orbit each have their individual strengths and weaknesses in the context of navigation. Closer to Earth, LEO offers less spreading loss and improved signal strength on the ground. On the other hand, being closer to Earth means that satellites have much smaller footprints. The GPS footprint is threefold larger than Iridium, corresponding to nine times more area covered. Hence, to achieve the same coverage as GPS with Iridium’s altitude, the LEO constellation requires an order of magnitude more satellites.
Another major difference between LEO and MEO is speed. A GPS satellite completes one Earth revolution every 12 hours while an Iridium one does so in only 100 minutes. The shorter the orbital period, the faster the angular rate (also called mean motion) and the more quickly satellites pass overhead.
The swift motion whitens multipath (making it more random–like white noise) as reflections are no longer effectively static over short averaging times. Geometric diversity also leads to effective Doppler positioning and is also desirable for carrier-phase differential GNSS, allowing for much more rapid resolution of integer cycle ambiguities.
Iridium-Satelles Satellite Time and Location (STL)
The STL service has been in operation since May 2016. Many from industry and government are already using this service to achieve a more robust PNT solution. This service will only continue to improve with the Iridium NEXT satellites under deployment; the first ten satellites of this generation were successfully launched in January 2017.
STL is a non-GNSS solution for assured time and location that is highly resilient and physically secure. STL utilizes the Iridium constellation to transmit specially structured time and location broadcasts. Due to their high RF power and signal-coding gain, the STL broadcasts are able to penetrate into difficult attenuation environments, including deep indoors.
Like GNSS signals, these broadcasts are specifically designed to allow an STL receiver to obtain precise time and frequency measurements to derive its PNT solutions. STL is able to augment or serve as a backup to existing GNSS PNT solutions by providing secure measurements in the presence of high attenuation (deep indoors), active jamming, and/or malicious spoofing.
Unlike the MEO GNSS satellites, Iridium uses 48 spot beams to focus its transmissions on a relatively small geographic area. The complex overlapping spot beams of Iridium combined with randomized broadcasts give a unique mechanism to provide location-based authentication that is extremely difficult to spoof.
The July cover story in GPS World magazine will explore all the above topics in more technical detail, and go further into the areas of signal strength in challenging environments, indoor time-transfer capability, and a section on looking forward.
The PNT service using Iridium is perhaps a sign of things to come. On the horizon are constellations like OneWeb which promise the next order of magnitude with 648+ satellites, slated for the 2020s. This most recent scale gives rise to better satellite geometry than GPS today with the added benefits of LEO.
The STL signal using Iridium sets a precedent that could lead to unparalleled navigation services that are robust due to the improved signal strength and precise due to the huge number of LEO satellites coming, each moving quickly and giving the geometric diversity needed to enable fast carrier-phase differential GNSS.
The need for such a service is already present. This would be enabling for the safety-critical autonomous vehicles under development that must operate in challenging urban environments and to a diversity of other future technologies and applications as well.
The report was commissioned by Innovate UK, the UK Space Agency and the Royal Institute of Navigation. It followed from the January 2016 accident referenced earlier, in which an error in the GPS signal from certain satellites, triggered by the decommissioning of one of those satellites, brought a number of key industrial servers to their knees. The episode lasted 12 hours.
