Author: Alan Cameron

Using the new interactive ‘GPS on Bench Marks’ map

The National Geodetic Survey (NGS) is now developing the 2022 transformation model. Once again, NGS requests the assistance of the surveying and mapping community. This column provides examples to explain the symbology and use of the new version of the GPS on Bench Marks program for developing the 2022 transformation tool.

My last column discussed the results of the Beta hybrid Geoid18 model, and the differences between the Beta model and the official hybrid geoid model, Geoid12B. It provided examples to explain the symbology of the Beta Geoid18 Web Map. It was noted that NGS analysts rejected stations based on pre- and post-modeled residuals but many times there wasn’t enough redundant information available to ensure the station should be rejected or used in the creation of the hybrid geoid model. As I have mentioned before, users should be commended for their participation in the GPS on Bench Marks program. The Geoid18 model is still in “Beta” so, hopefully, users will continue their support by evaluating the Beta hybrid geoid model and reporting their issues to NGS. Saying that, NGS’ GPS on Bench Marks program is now in a different phase.

NGS held a webinar in July on the latest GPS on Bench Marks program for developing the 2022 Transformation tool. The webinar was recorded and users can find the presentation here. This was an excellent webinar and explained the functions of the web map. I would encourage readers to watch the webinar. It is an hour long but is worth while watching. See Figure 1 for information on the webinar.

Figure 1: GPS on Bench Marks:2022 Transformation Tool Campaign Webinar. (Photo: National Geodetic Survey) — Figure 1: GPS on Bench Marks:2022 Transformation Tool Campaign Webinar (Photo: National Geodetic Survey)

As in the past, the NGS on Bench Marks program can be accessed from NGS’ web page (see Figure 2). The user clicks on the “GPS on Bench Marks” button to access the program’s web page.

Figure 2: NGS Home Web Page (Photo: National Geodetic Survey)

Figure 3 depicts the home web page of the GPS on Bench Marks Program.

Figure 3: GPS on Bench Marks Home Web Page (Photo: National Geodetic Survey)

The web page provides several reasons why users should continue to participate in the GPS on Bench Marks program. Figure 4 lists three reasons for helping NGS develop the 2022 Transformation Tool.

Figure 4: Excerpt from GPS on Bench Marks Home Web Page

GPS on Bench Marks

Help improve the National Spatial Reference System (NSRS) and prepare for the NSRS modernization in 2022 by participating in the GPS on Bench Marks (GPS on BM) for the Transformation Tool campaign. Your efforts will support the following objectives:

• Improve the 2022 Transformation Tool, >which will enable conversions from current vertical datums to the North American-Pacific Geopotential Datum of 2022 (NAPGD2022) and will be integrated into the NGS Coordinate Conversion and Transformation Tool (NCAT).

• Update Passive Control Status: mark recoveries and shared solutions provide NGS and other users of the NSRS with insight into the health of the passive control network and updated information for project planning.

• Automatic Reprocessing in 2022: Shared data will be automatically reprocessed and given new coordinates after the NSRS modernization occurs in 2022.

I’d like to highlight a few of the benefits for participating in the GPS on Bench Marks program.

(1) Improve the 2022 Transformation Tool, which will enable conversions from current vertical datums to the North American-Pacific Geopotential Datum of 2022 (NAPGD2022) and will be integrated into the NGS Coordinate Conversion and Transformation Tool (NCAT).

> A goal of the transformation tool is to provide a model that will allow users to convert from the current North American Vertical Datum of 1988 (NAVD 88) to the new North American – Pacific Geopotential Datum of 2022 (NAPGD2022). The more bench marks that are occupied by GNSS and included in OPUS Shared solutions will enable NGS to generate a more detailed relationship between NAVD 88 and NAPGD2022. This will provide an accurate transformation tool in local areas which will facilitate the implementation of NAPGD2022 in surveying and mapping products and services.

(2) Update Passive Control Status: mark recoveries and shared solutions provide NGS and other users of the NSRS with insight into the health of the passive control network and updated information for project planning.

> An important part of the GPS on Bench Marks program is that it provides an indication of the status of the station. The last time a bench mark was leveled to varies greatly across the Nation. Many of stations in NGS’ Integrated Dataset haven’t been visited in over 50 years. The GPS on Bench Mark program can be useful to identify stations that have moved since the last time it was part of a leveling project. The mark recoveries will provide the latest status of a station which will help others in future project planning. More important, in my opinion, is that the OPUS shared solutions will identify stations that no longer have valid NAVD 88 published heights, and should be used with caution and flagged with a warning

(3) Automatic Reprocessing in 2022: Shared data will be automatically reprocessed and given new coordinates after the NSRS modernization occurs in 2022.

>> Any station that is part of the GPS on Bench Marks program and included in the OPUS Shared solution database will be given 2022 coordinates. This means that users will not have to resubmit their data to obtain the new coordinates in the new 2022 reference frames. This information will be useful during the implementation phase of the 2022 reference frames.

As in the past, NGS is developing web-based products and services to facilitate users incorporating their data into the National Spatial Reference System (NSRS). They have developed a GPS on Bench Marks Web Map Application to inform users which stations they would like occupied by GNSS equipment. They realize that everyone is busy so they are trying to provide information, in near real time, on stations that have been occupied to reduce users occupying a station that already has two occupations. Figure 5 depicts the buttons that will connect the user to an interactive web map application. There are several ways the user can access the application: (1) click on the link titled “Web Map Application” – the red rectangle and arrow in the box titled “GPS on Bench Marks Web Map Application Site,” (2) click on the figure of the web based application – see the blue ellipse and blue arrow in the box, and (3) download the prioritized marks in XLS or Shape file format – see the green pentagon and green arrow in the box.

Figure 5: GPS on Bench Marks Web Map Application Site (Photo: National Geodetic Survey)

Clicking on the Web Map Application button or picture will direct the user to a new website. It informs the user that they are leaving a U.S. Government Web Site for another site. See Figure 6. The user can either click on the statement or just wait until they are redirected the website. (See Figure 7.)

Figure 6: Clicking on the Web Map Application Button or Picture (Photo: National Geodetic Survey)

Figure 7: GPS on Bench Marks For the Transformation Tool Interactive Web Map (Photo: National Geodetic Survey)

Just click on the “OK” button to remove the splash screen. You can click the button “Do not show this splash screen again” so it doesn’t show up every time you access the web page. At the bottom of the web map is a legend that provides information about the map and allows the user to select various options. Figure 8 provides an example of legend buttons. The information box appears by clicking on a particular icon in the legend bar (the arrows indicate the icon and information box for that icon).

Figure 8: Legend on GPS on Bench Marks Web Map Application Site (Photo: National Geodetic Survey)

There’s a lot of information provided in the information box. There’s a scroll bar on the right side of the box that provides the entire write up. Figure 9 provides several sections of the write up. I’ve highlighted sections in the write up to emphasis what NGS is trying to accomplish. NGS’ goal is to minimize the amount of work performed by users and maximize the amount of GNSS data provided to the development of the 2022 transformation tool.

First, NGS has prioritized marks at two spatial resolutions: 10 km and 2 km. They want to reach a 10 km density to provide good national accuracy and a 2 km level to improve local accuracy. The Interactive Web Map allows users to zoom down to a level to identify individual stations selected by NGS. A 10-kilometer hexagonal lattice was developed to define the desired data density on the ground. For each hexagon, the goal was to identify a primary mark and a list of up to 4 secondary marks. The primary mark for each hexagon was added to the priority mark list. Secondary marks are listed and should be observed in cases where the primary mark cannot be found or is unobservable.

To reduce duplication, when a single mark within a 10 km hexagon has two GPS observations that meet NGS requirements, that hexagon is marked as done and the station is removed from the prioritized list. This will help to reduce the number of surveyors occupying the same station over and over again, and increase the number of prioritized stations occupied with GNSS. After a 10-kilometer hexagon is marked as done, a group of up to thirteen 2 km hexagons is generated to define the opportunities to densify the model with additional marks.

To assist in the selection of stations to be part of the GPS on Bench Marks program, NGS has prioritized stations as Priority A and B. Priority A being more important than priority B for the development of the 2022 transformation tool.

Figure 9: Excerpts from GPS on Bench Marks for the Transformation Tool Technical Details

For questions or comments on this tool please email NGS at [email protected].

NGS has developed a prioritized list of bench marks on which new GPS observations will be most helpful to develop the best transformations between the current vertical datums and the modernized NSRS in 2022.

• NGS has labeled marks as Priority A or B based on the quality of previous geodetic measurements, the stability of the mark, and other criteria. GPS observations on Priority A marks will be the most helpful.

• NGS has also prioritized marks based on two spatial resolutions: 10 km and 2 km. 10 km spacing will provide good accuracy at the national scale. Users can improve local accuracy even more by collecting data at the 2 km level.

• NGS will build the transformation tool with data submitted by December 31, 2021. The tool will interpolate over areas without GPSonBM data, meaning that the transformations will be less accurate in those areas.

Priorities A and B

Priority A
Priority A marks meet the following specific criteria from their datasheets and are most likely to be used to create the transformation tools:
• Vertical Order: FIRST, SECOND
• Stability: A, B, C
• Satellite: USEABLE
• Last Recovery Condition: excluding “MARK NOT FOUND”

Priority B
Priority B marks are lower quality marks that will only be considered for use in the transformation tool to fill data gaps if no other data exists in the region.

Spatial Resolution
NGS has also prioritized marks at two spatial resolutions: 10 km and 2 km. NGS wants to reach a 10 km density to provide good national accuracy. Additionally, users can help improve local accuracy by collecting data at the 2 km level.

To prioritize marks based on the two spatial resolutions, NGS created the following system:
• A 10-kilometer hexagonal lattice was developed to define the desired data density on the ground and help select appropriate marks within those areas throughout the U.S. and territories.
• Hexagons with appropriate bench marks were identified.
• For each hexagon, a primary mark was selected and a list of up to 4 secondary marks — if available — were identified. The primary mark for each hexagon was added to the priority mark list. Secondary marks are listed and should be observed in cases where the primary mark cannot be found or is unobservable.
To communicate when observations in a hexagon have been completed, the following process was developed:
• Once a single mark within a 10 km hexagon has two GPS observations that meet the requirements, that hexagon is marked as done and the observed mark is removed from the prioritized list.

• Once a 10 km hexagon is marked as done, a group of up to thirteen 2 km hexagons is generated to define the opportunities to densify the model with additional marks.
• In each of the 2 km hexagons, a primary mark is identified and a list of secondary marks is provided in case the primary mark cannot be found or is not observable. The new primary marks are added to the priority mark list. The number of 2 km hexagons will vary since not all areas have bench marks inside the 2 km lattice. See graphic below:

Clicking on the Web Map Applications “Instructions” button will provide a summary of all of the tools available on the Web Map. See the arrow in Figure 10. The instruction page provides a lot of information and explains the function of each tool.

Figure 10: GPS on Bench Marks Web Map Instructions Site (Photo: National Geodetic Survey)

Figure 11 provides an excerpt from that web page. All of the icons on the Web Map are explained on a mock up of a sample map in the beginning of the Instruction web page.

Figure 11: GPS on Bench Marks Web Map Instructions List of Tools (Photo: National Geodetic Survey)

The list of detailed descriptions of the tool is fairly long so I’ve provided some of the descriptions in Figure 12. The reader is referred to this page for the descriptions of all of the tools.

Figure 12: Partial List of Descriptions of GPS on Bench Marks Web Map Instructions Tools

Legend
Clicking this button will display the legend for all of the active layers displayed on the map.

Layer List
Clicking this button will bring up the list of available layers to display on the map. By default, only the Priority List of marks at 10 km spacing appears. Users can select other layers to display on the map by clicking on the box to the left of the layer name. Once clicked, the box will show a check mark, and all layers with check marks are displayed on the map.

Layer Descriptions:
• Priority List 10 km – Marks requested for national coverage
• Priority List 2 km – Marks requested to densify local areas
• Priority List Done – All marks with enough observations to be considered for use in the Transformation Tool.
• Hexagons 10 km – Areas where GPSonBM data is still requested to complete broad national coverage
• Hexagons 10 km – Done – Areas where sufficient data exists
• Hexagons 2 km -Areas where GPSonBM data may still be submitted to increase local accuracy of the transformation tool.
• Hexagons 2 km – Done – Areas where sufficient data exists.

Working with the Layer List
Clicking on the ellipsis to the right of each layer opens a window with actions for that layer. Set visibility range allows the user to set the zoom level at which each layer appears. By default the visibility ranges are set to prevent too much data from being plotted at once which would slow down the application. Users with fast internet connections can change the visibility range to allow data to be displayed when zoomed out far enough to see the extents of larger states.

Mark Selection Tool:

This tool provides several options for selecting marks. First, change the layer to select from, click in the box to the left of the layer name. Click the green Select box and choose a selection method, then use the mouse to left-click on the map to draw the selection region. Selected marks’ icons will turn blue. Once marks are selected, click on the ellipsis to the right of the layer to open menu of actions that can be performed with selected marks. Using this menu, selected marks can be exported into csv, JSON, and GeoJSON formats.

Attribute Table
This button opens a table at the bottom of the screen that displays all the information available on each mark.

Filters

By State, County, and PID: This tool allows the user to filter the marks on the map down to specific states, counties, or PIDS. After selecting the filter option, click on the switch at the top right of the filter box and the map will pan and zoom to the selected area. If the marks do not appear on the map, try zooming in until they appear.

Figure 13 provides four different options of the icons on the bottom of the web map. They include the “Legend,” Layer List,” Select Priority List,” and Filter by State. These options help the user focus on a particular area of interest. I would encourage the user to familiar themselves with each of these options because they help will make it easier to navigate the map and identify priority stations.

Figure 13: Example of Several Options on the Legend on GPS on Bench Marks Web Map Application Site (Photo: National Geodetic Survey) — Figure 13: Example of Several Options on the Legend on GPS on Bench Marks Web Map Application Site. Examples below are for the “Legend,” Layer List,” Select Priority List,” and Filter by County.” (Photo: National Geodetic Survey)

Another important icon located at the bottom of the Web Map opens an attribute table of the bench marks. (See Figure 14). Once you open the Attribute table tool (see the red arrow in the box), a table of attributes of the stations appears at the bottom of the screen. If you click on a station in the table, the station gets highlighted on the map (see the blue arrow in the box). NGS’ Web Map Application makes it very easy to locate potential stations in a user’s area of interest.

Figure 14: Example of the Attribute Table on the Legend on GPS on Bench Marks Web Map Application Site (Photo: National Geodetic Survey)

When the user clicks on the Layer List tool, they can select which priority list they would like to see plotted on the map. They can click on the “More Info” button to obtain the latest NGS Datasheet. Figure 15 provides an example of A and B stations from the 10 km priority list in the Loudoun County, Virginia, region. The map highlights priority A and B stations; the user can than find more information about a specific station by clicking on the map.

Figure 15: Excerpt from GPS on Bench Marks Web Map Layer List - Priority List 10 km (Photo: National Geodetic Survey) — Figure 15: Excerpt from GPS on Bench Marks Web Map Layer List – Priority List 10 km (Photo: National Geodetic Survey)

A very interesting feature is that once a station is classified as done in a 10 km hexagon, the hexagon is colored green and flagged as done. There is no longer a requirement to occupy a station in that hexagon to assist the 2022 transformation tool for the National level of accuracy. See Figure 16 to see a 10-km hexagon labeled as “Done.” Note that the station considered “Done” is labeled with a white circle.

Figure 16: An Example of a 10-km Hexagon in the Montgomery County, Maryland, and Loudoun County, Virginia, Region (Photo: National Geodetic Survey)

Now the user can focus on the 2-km hexagon boxes to identify stations to improve the local accuracy of the 2022 transformation tool in their area of interest. Figure 17 provides an example of the 2-km hexagons with priority marks plotted within each 2-km hexagon. Once again, the symbology indicates A and B stations, and the 2-km hexagons that need more observations and the hexagons that are labeled as “Done.”

Figure 17: An Example of 2-km Hexagons in the Montgomery County, Maryland, and Loudoun County, Virginia, Region (Photo: National Geodetic Survey)

NGS’ goal is to update the Interactive Web Map in “Near Real Time.” Of course, there’s always going to be some lag time from the time the user uploads their data into the OPUS Shared solution database to when the NGS 2022 Transformation Team reviews the data to ensure the results meet NGS’ criteria. Once again, NGS wants to minimize the amount of duplicate work performed by surveyors and maximize the number of stations contributing to the development of the 2022 transformation tool.

This newsletter highlighted the next phase of NGS’ GPS on Bench Marks program; that is, the development of the 2022 transformation model. The newsletter provided examples to explain the symbology and use of the new version of the GPS on Bench Marks program. It provided web links to material explaining the new GPS on Bench Marks program such as NGS’ July 2019 webinar on the latest GPS on Bench Marks program for developing the 2022 Transformation tool. NGS has done a tremendous job of explaining the importance, process, and results of the GPS on Bench Marks Program. Several of my previous newsletters have highlighted the NGS GPS on Bench Marks program and how users have supported the development of the hybrid Geoid18 model: Hopefully, this support will continue to develop the best possible 2022 Transformation Tool.

August 7, 2019

Without Galileo, life goes on

Galileo’s Control Centre in Fucino is used to oversee the satellites’ navigation payloads and services. (Photo: ESA)

Global markets learned something important from the brown-out of Galileo signals over a week’s time in July: Life goes on without a hiccup in the absence of the European GNSS.

Very unfortunately for the backers and boosters of Galileo, this message will reverberate down through the years. If vital affairs proceed unaffected by Galileo’s travails, or triumphs for that matter, who needs it? The response, a shrug. I’m tempted to say a Gallic shrug, were it not that the Gauls, the French, are prime among the system’s boosters and backers.

I’m among that number as well. Galileo and I have known each other all our lives, all our professional lives. When I started on this magazine 19 years ago, the first story I edited was on Galileo’s public-private partnership.

Galileo then was just a collective gleam in several politicians’ and scientists’ eyes. Look how far it has come: 20 satellites flying in various operational or testing states.

The European GNSS Agency was very careful to point out during the crisis that Galileo is in its initial services phase. Its signals are available for use in combination with other GNSS and are not intended to provide a complete solution by themselves. This status is expressly designed to allow for “the detection of technical issues before the system becomes fully operational.”

So, it doesn’t count. Because, the game hasn’t really started yet. Right?

Not quite.

Because this episode occurred, it will be remembered. Because it lasted so long, it will be factored. Because the official announcements about it were so obscurantist, the system may find it more difficult to regain trust.

Of course a full, careful, in-depth investigation must take place before officially announcing what caused the debacle. But more than was said could surely have been said, during the crisis. A full week now, as of this writing, after the week-long outage concluded, we still have no indication as to which piece of ground equipment or software failed and why there wasn’t a smooth transition from the Italian to the German control station.

Redundancy was built into the system to preclude exactly such failures as this. Why didn’t redundancy work?

Transparency is a rhyming word that goes well with redundancy.

Trust — corporate confidence — is fundamental to installation in multi-GNSS chips, boards, modules, all manner of devices. Four systems compete for spots at a table that may comfortably fit only three. Even three could be a stretch.

GLONASS suffered a much shorter (11-hour) timing glitch in 2014, and has yet to climb back into the public-confidence ring.

Here’s a very public lesson in transparency: When the GPS satellite SVN49 failed rather spectacularly in 2009, the GPS Directorate was very forthcoming, almost embarrassingly so, about what happened and why. GPS never lost a step in the public’s and the industry’s eyes.

July 25, 2019
AFRL tests Chimera to battle spoofers and hackers

L1C Signal Could Be Watermarked as Countermeasure

The U.S. Air Force will load a new signal feature, designed to make spoofing detectable, aboard a satellite that will broadcast it from space as a security overlay for the GPS L1C signal, but not until 2022 at the earliest.

The Chips Message Robust Authentication (Chimera) is now in testing under the auspices of the Air Force Research Laboratory (AFRL), getting ready to fly on the Navigation Technology Satellite 3 (NTS-3), which will trial a number of new PNT techniques and technologies.

Chimera inserts encrypted digital signatures and watermarks within the L1C signal. A GPS receiver with the requisite additional capability for this purpose can then detect whether the signal is real or fake and also authenticate the location of a GPS receiver that is remotely located.

This key feature could provide a defense against hacking by blocking access from anyone unable to prove they are at an anticipated or licensed site. Hacking, of course, is a growing threat to all sorts of infrastructure: financial, security, utility grid and more.

Presentation slide from PNT Advisory Board briefing by Logan Scott.

Consultant Logan Scott first proposed the Chimera technology in 2003, when he affirmed that “Some of the spoofing detection measures in wide use offer a false sense of security. Authenticatable signal architectures are needed.” In June, he made a presentation to the PNT Advisory Board: “The Role of Civil Signal Authentication in Trustable Systems.” The two slides accompanying this article appeared in that presentation.

“Chimera represents a fundamental paradigm shift in PVT security paradigms,” Scott related in a subsequent conversation. “Trust takes time and memory on a personal level and, in this case, in GNSS signals, too.

“You don’t trust somebody as soon as you meet them. Over a period of time, you get to know them. If you can’t remember anything, you can’t develop trust either.”

“In the GNSS world, there are a lot of applications where you don’t need output in real time,” Scott said. “For example, to align an inertial. The inertial provides the real-time aspect. You don’t want to send anything to the IMU that is factually incorrect. When building to aid inertial, I can afford to have a delay from real time as long as I tell it where it was 10 seconds ago. The power of that is, if I don’t have to give real-time output, I can ponder and think about things.

“If a spoofer attacks, there’s an evolution that happens there. If I, as the receiver, can see the developing scenario, and how it starts to look at little screwy, I can stop and not send anything to the IMU that might corrupt it.”

How It Works. The core concept of Chimera involves the satellites sending encrypted watermarks, encoded into the signal by the satellite. After a slight delay, the satellite sends the key used to generate those encrypted watermarks. Once a key is sent, the system changes the key.

Since the receiver has already recorded the signal with its watermarks before the key is sent, spoofers cannot know the correct key ahead of time, in time to insert correct watermarks of their own. This means that any spoofed signals can be easily spotted: either the subsequent key won’t match up with the spoofed watermarks, or there will be no watermarks at all.

“Another reason it’s hard for someone to generate these watermarks on their own is because the signal is buried below the noise,” added Scott. “The watermarks are hidden.”

A number of different time delays between signal and key are possible within this concept and within the general set-up of GPS. Scott and the AFRL have, for various practical reasons, provisionally settled on a 6-second delay on the fast watermark channel and a 3-minute delay for the slow watermark channel.

The signal enhancement could be incorporated into the Wide Area Augmentation System (WAAS). This has yet to be fully determined, but this route would lead to a faster implementation of Chimera. Scott thinks that going the WAAS route could bring Chimera capability into action within two years.

The AFRL, however, is looking at a much longer timeline. The NTS-3 satellite, where it first intends to test Chimera, will not launch until 2022 — three years hence. And that’s only a test, not an enactment or a system-wide implementation.

Slide: Logan Scott

Verification. One key benefit for commercial entities, particularly those in financial infrastructure and other systems that increasingly fall victim to hacking, is that Chimera gives them the ability to verify customers’ or partners’ locations before granting any kind of access. The customer’s or other erstwhile user’s GPS receiver would record the full signal, including the watermarks, and transmit that data to the company, entity or data center needing location verification, before the keys are published. Each combination of watermarks and signals is unique to the place where it was recorded, thus it is possible to tell whether the user is actually where they say they are, or in an authorized or pre-identified location before granting access or accepting further input (such as commands).

Scott claims that Chimera affords a 99.9% probability of detecting spoofers. “I have a 99.9% chance of detecting that the watermark is not there, because they don’t know how to generate it. This is based on how you’re processing the signal. It’s designed to be very flexible in how the receiver uses the signal.”
Just One Problem. Receiver manufacturers will have to develop new Chimera-capable receivers, and customers will have to buy them. An additional cost for the added processing, above and beyond that required for normal GPS operation, is unavoidable.

And a Hiccup. Chimera, while an acronym, is as a name perhaps not a totally felicitous choice. In Greek mythology, the chimera is a fire-breathing female monster with a lion’s head, a goat’s body, and a serpent’s tail. These historic ancestors have evolved into the word’s more current use: a thing that is hoped or wished for but that is in fact illusory or impossible to achieve.

AFRL Wants Your Opinion. The Air Force Research Laboratory seeks feedback from the PNT community on the Chimera enhancement for the L1C signal. The specification is here. And, you can download a comment form

July 24, 2019
What value does precise timing hold for GPS?

Image: Lockheed Martin

This just in: a Final Report on the Economic Benefits of GPS. Sponsored by National Institute of Standards and Technology, the study began a couple of years ago, conducted by RTI International, one of the nation’s oldest and largest research firms.

The report runs 306 pages and examines the benefits derived from GPS by 10 U.S. industries: agriculture, electricity, finance, location-based services, mining, maritime, oil and gas, surveying, telecommunications and telematics.

Among other issues, the research explored the potential effect of a 30-day GPS outage, assuming that other GNSS would be disrupted as well, and found the outage would have a $1 billion per-day impact. The 30-day outage scenario was specifically added at the request of the National Executive Committee for Space-Based Positioning, Navigation and Timing.

While a disruption lasting 30 days seems unlikely, as the report says, “understanding the relative magnitude of potential impacts is important for making informed decisions about investments in back-up systems and contingency plans.”

Relating a sense of the full report is beyond the scope of this small space, but I encourage all readers to download it (link at ) and examine it either in its entirety, or in its applicability to your particular industrial sector. Here

I’ll focus briefly on GPS’s precise timing capability, which supports telecommunications.

Precise timing enables service providers to more efficiently use available spectrum and deliver high-speed wireless services. Given American society’s intensive use of these two lifelines, it is not surprising that benefits related to telecommunications are substantial: $685 billion, more than twice that of the second-ranked industry in terms of economic benefits, and more than half of the total benefits.

GPS reduces/eliminates dropped calls and increases bandwidth, enabling more advanced networks such as 4G LTE, which we now have, and 5G, which is coming at breakneck speed.

Wireless network infrastructure has evolved to rely heavily on GPS. In fact, GPS has shaped the telecommunications industry: its technology has evolved around GPS. See last month’s cover story for more details.

Interestingly, to calculate the economic benefits of GPS in the telecom sector, the researchers used two indices as a baseboard: radio spectrum auction data showing telecom service providers’ willingness to pay (WTP) for spectrum to provide 4G LTE, and consumers’ WTP for the broadband speeds enabled by 4G LTE. Both these numbers are going up, up, up.

While the number of wireless subscribers in the United States increased at a respectable rate from 2009 to 2017 — about 35% — the average bandwidth used by those subscribers expanded at an astonishing 2,200%!

Experts interviewed on the prospect of an extended GPS outage agreed that, eventually, a user would have to remain stationary to maintain a wireless connection, albeit a degraded one. After some time of steady degradation of quality of service, wireless service would cease to function altogether.

It’s hard to imagine which would be worse: a world without mobile telecoms, or one without GPS. However, we don’t have to strain, because in this case we would lose both.

To avoid the unimaginable…plan, plan, plan, and backup, backup, backup.

July 24, 2019
Galileo picks itself up and moves on

Galileo Ground Control Center, Fucino. Photo: GSA

Galileo Initial Services have been restored after a week-long signal outage, according to a statement released on July 18 by the European GNSS Agency (GSA).

“Commercial users can already see signs of recovery of the Galileo navigation and timing services…although some fluctuations may be experienced until further notice.”

After a signal outage that began on July 11, efforts to restore services reportedly found a malfunction in the calculation of time and orbit predictions (ephemeris).

Why the error affected both Precise Timing Facilities (PTFs) within the Galileo ground control system, at Fucino in Italy and Oberpfaffenhoffen in Germany, has not been explained. System redundancy in the form of such doubled facilities was meant to prevent such breakdowns.

The GSA statement continues:

“Galileo Initial Services have now been restored. Commercial users can already see signs of recovery of the Galileo navigation and timing services, although some fluctuations may be experienced until further notice.

“The technical incident originated by an equipment malfunction in the Galileo ground infrastructure, affecting the calculation of time and orbit predictions, and which are used to compute the navigation message. The malfunction affected different elements on the ground facilities.

“A team composed of GSA experts, industry, ESA and Commission, worked together 24/7 to address the incident. The team is monitoring the quality of Galileo services to restore Galileo timing and navigation services at their nominal levels.

“We will set an Independent Inquiry Board to identify the root causes of the major incident. This will allow the Commission, as the programme manager, together with the EU Agency GSA to draw lessons for the management of an operational system with several millions of users worldwide.”

The full statement, including links to previously issued Notice Advisories to Galileo Users (NAGUs) is available here on the GSA website.

July 18, 2019
Galileo’s initial services rocky patch continues

The Galileo signal outage, ongoing since Thursday, July 11, has been attributed to a problem with the system’s ground infrastructure, according to an announcement by the European GNSS Agency (GSA). “Experts are working to restore the situation as soon as possible,” states the GSA. “An Anomaly Review Board has been immediately set up to analyze the exact root cause and to implement recovery actions.”

No update has appeared at this time as to when service will resume.

[Photo: Galileo’s Ground Mission Segment in the Fucino Control Centre in Italy oversees Galileo navigation services and satellite payload operations. Photo: Telespazio.]

The announcement points out that Galileo is currently in its initial services phase, wherein its signals are available for use in combination with other GNSS and do not provide a complete solution in and of themselves. This status is expressly designed to allow for “the detection of technical issues before the system becomes fully operational,” according to the GSA.

Indeed, experiments undertaken with Galileo-capable smartphones found that these devices excluded Galileo participation in their position solution. This is likely true of commercial receivers as well, which employ sophisticated signal checks as well as following system notice advisories, which have been issued in this case.

“For each constellation, there is a defined maximum age of ephemeris that is considered valid,” explained Sandy Kennedy, vice president, innovation at NovAtel. “Once an ephemeris is too old, our receiver will deem it invalid. Measurements made to satellites without a valid ephemeris are not allowed to contribute to the PVT solution. We noticed the missing Galileo ephemeris within 3 hours of the broadcast stopping. It wasn’t the NAGU that alerted us to the problem.”

The company posted a bulletin to its website on Friday afternoon, July 12, stating: “During this time [without ephemeris], NovAtel receivers will continue to track Galileo signals, but without a valid ephemeris, the signals are not included in the position solution. . . . Once the Galileo service returns to normal and transmits ephemeris information, NovAtel receivers will revert to normal operation.”

The experiments mentioned above were conducted by the Navigation Signal Analysis and Simulation (NavSAS) Group at Fondazione LINKS (formerly the Istituto Superiore Mario Boella) and the Politecnico di Torino. In their account they state that, using a software receiver that tracked the Galileo signals in space (SISs), “the position solution computed using both the GPS and Galileo constellation is affected by errors on the order of 500 meters or even more.”

In a detailed technical analysis, the NavSAS Group found three other curious and unexpected aspects of the situation, all explored and illustrated at the Group’s posting.

July 15, 2019
Galileo down over weekend

The entire Galileo system suffered an unexpected and hitherto unexplained signal outage, beginning on Thursday, July 11, at 1 p.m. Central European Time. At about that time, users noticed that all ephemeris stopped broadcasting, and then a Notice Advice to Galileo Users (NAGU) appeared:

NAGU Subject: Service Degradation

Satellite Affected: ALL

Event Description: Until further notices, users may experience service degradation on all Galileo satellites.s this means that the signals may not be available nor meet the minimum performance levels defined in the service definition documents and should be employed at users’ own risk. The nominal service will be resumed as soon as possible.”

The signal outage has persisted for more than two days (as of Saturday) and as yet no word has emerged as to the cause or duration of the signal outage.

On the evening of July 13, a second NAGU appeared, saying simply that “Until further notice, users experience a service outage. the signals are not to be used.”

On the European GNSS Service Centre’s constellation status page, 22 Galileo satellites are listed as “Not Usable” with cause being “Service Outage.”

[Photo: Galileo Control Center, Oberpfaffenhofen. Photo: GSA]

July 14, 2019
Aircraft lands autonomously without ground assistance

A German research team successfully demonstrated a completely autonomous airplane landing in May, without assistance from any ground-based systems, fulfilling a key step towards autonomous air traffic and the much-bruited Urban Air Mobility (UAM).

An optical reference system, encompassing a camera in the normal visible range and an infrared camera for conditions with poor visibility, combined with GPS to bring the modified Diamond DA42 in for a safe, unpiloted landing at the Diamond Aircraft airfield in Wiener-Neustadt, Austria.

The team, from the Technical University of Munich (TUM) and the Technische Universität Braunschweig, formed the project they call C2Land with funding from the German federal government. Two 2019 conference papers by the researchers, cited at the end of this article, give the technical underpinnings of the C2Land system.

What’s New

Automatic landings by both commercial aircraft and small planes can and do take place at major airports with the Instrument Landing System (ILS) infrastructure to guide aircraft in with sufficient precision. Ground antennas send radio signals to the autopilot to make sure it navigates to the runway safely. Procedures in development to use GNSS alone to make autonomous landings also require a ground-based augmentation system.

But systems such as these are too expensive for small airports that will conceivably carry the major share of UAM: automated air freight transport and autonomous flying taxis.

What needs to happen before George Jetson air taxis become a reality? UAM will take place in the zone 500 to 5,000 feet above ground, transporting one to five passengers or cargo over distances of five to 50 miles. The vision shared by most UAM stakeholders, a group that includes NASA and the FAA, involves vertical take-off and landing rather than conventional “glide” takeoff and landing, but precise navigation to the landing spot is critical in both cases.

“Automatic landing is essential, especially in the context of the future role of aviation,” said Martin Kügler, research associate at the TUM Chair of Flight System Dynamics.

Fly-by-wire systems, semiautomatic and typically computer-regulated systems for aircraft navigation, use GPS signals for positioning. But since GPS is susceptible to errors, interference, and obstruction, it is not solely sufficient for landing procedures. Current GPS approach procedures require that human pilots resume control over the aircraft at 60 meters altitude, and land the aircraft manually.

To enable completely automated landings , the TU Braunschweig team designed an optical reference system: two cameras, one in normal visible range and one infrared camera for poor visibility conditions. Custom image processing software lets the system determine where the aircraft is relative to the runway based on the camera data it receives. Additional functions were integrated in the software, such as comparison of data from the cameras with GPS signals, calculation of a virtual glide path for the landing approach and flight control for various phases of the approach.

Visual Recognition

Test pilot Thomas Wimmer, who sat through the procedure with his hands folded, said “The cameras already recognize the runway at a great distance from the airport. The system then guides the aircraft through the landing approach on a completely automatic basis and lands it precisely on the runway’s centerline.”

The researchers presented their system in two papers at the Institute of Navigation’s 2019 Pacific PNT Meeting in April:

“Model-based Threshold and Centerline Detection for Aircraft Positioning during Landing Approach,” by S. Wolkow, M. Angermann, A. Dekiert, and Ulf Bestmann; and

“Linear Blend: Data Fusion in the Image Domain for Image-based Aircraft Positioning during Landing Approach,” by M. Angermann, S. Wolkow, A. Dekiert, U. Bestmann, and P. Hecker.

Summaries of each paper are here. The full papers are available at www.ion.org/publications/browse.cfm.

July 9, 2019
Israel accuses Russia of spoofing in its airspace

Photo: Ministry of Defense of the Russian Federation

Israeli security officials publicly accused Russia of disrupting and spoofing GPS signal reception in Israeli airspace throughout the month of June. The electronic warfare at which Russia is known to be adept was reportedly traced to the Khmeimim Air Base in Syria, where Russia maintains and actively flies a large number of warplanes on behalf of the Syrian government. The base is approximately about 350 kilometers (217 miles) north of Ben Gurion, so if the accusation is true, fairly powerful equipment is behind the attack.

Both Israeli and other-nationality airline pilots have reported interruptions in GPS reception during take-off and landing at Tel Aviv’s Ben Gurion International Airport. The Israeli Airline Pilots Association labeled the interruptions a spoofing attack, causing airplane receivers to report false positions.

The International Federation of Air Line Pilots’ Associations issued a Notice to Airmen: “GPS signal loss affects RNAV arrivals and departures and may create numerous alerts for systems that rely on internal position accuracy. Flight Crews should be aware of the potential risk, avoid distractions, and plan for alternative procedures as necessary.”

Pilots have since for the most part relied on Instrument Landing System, a precision runway approach aid based on two radio beams which together with both vertical and horizontal guidance during an approach to land at Ben Gurion International Airport.

The Israeli Airports Authority stated that the GPS attacks affected only airborne crews and not terrestrial navigation systems, and that they occur only during daytime.

The Russian ambassador to Israel has denied the accusations.

In April, a U.S. research institute, the Center for Advanced Defense Studies, documented more than 10,000 separate incidents of GPS disruption on Russian soil, in northern Scandinavia and in the Middle East between February 2016 and November 2018. It said Russia was “pioneering” the technique to “protect and promote its strategic interests.” GPS World summarized the report here, stating that “The Russian Federation is growing and actively nurturing a comparative advantage in the targeted use and development of GNSS spoofing capabilities to achieve tactical and strategic objectives at home and abroad.”

Tie-in with Iran Tensions. Meanwhile the Helsinki Times reported that researchers at the Finnish Geodetic Institute noticed unusual power variations in the GPS signal on June 20 and 21: “an increase of up to 10dBHz in the carrier-to-noise ratio readings comparing with the usual daily values.” Normally the variations are between -0.5 and 0.5 dBHz.

The same findings were communicated to the research community by Peter Steigenberger, senior scientist at the German Aerospace Center, DLR:

“Based on carrier-to-noise density ratio observations (C/N0) of IGS receivers, we observed global flex power operations on June 20 and 21, 2019. Flex power started subsequently for all healthy Block IIR-M and IIF satellites on June 20 between 15:18 and 17:49 UTC. C/N0 of the P(Y)-code tracking increased by roughly 10 dB for all healthy Block IIR-M and IIF satellites whereas C/N0 of the C/A-code decreased by about 2-3 dB for the healthy IIR-M satellites only. The changes in power levels are similar to flex power mode III discussed in “Steigenberger P, Thölert S, Montenbruck O. (2019) Flex power on GPS Block IIR-M and IIF, GPS Solutions, doi:10.1007/s10291-018-0797-8″. All satellites returned to normal power levels on June 21 between 6:00 and 10:00 UTC.”

On June 20, a US military drone was downed down by Iranian missiles. On June 21 President Trump tweeted that he had called off a dawn attack on Iran that day.

Whether the spoofing affecting Israeli airspace has any connection to building tensions 1,500 kilometers to the east is unknown.

June 29, 2019
Last call for State of the Industry — and $100 gift cards

Early polling results are in, and trends have emerged. Don’t absent yourself from this exercise in democracy. Make your views known on the state of the PNT industry before it’s too late — July 4 will be too late — and earn a chance at a $100 gift card.

With such questions as “Is your organization taking steps to ensure continuity of PNT availability in the event of a disruption in GNSS service?” and “What is the biggest challenge for the UAV industry?,” the survey takes the pulse of engineers, executives, designers, integrators, product managers and more across the industry. We’re looking to the horizon, seeking to identify the challenges that will guide us all into the next Big Thing.

Go to the 2019 State of the Industry Survey page and answer just slightly over 20 questions. Not only will you help create the future, you’ll help create your own chance at wealth. All who wish will be entered in a random drawing for two $100 gift cards.

June 28, 2019
Global BeiDou grows to 21 with latest launch

Seven-ninths of the way there! The 21st satellite of the BeiDou-3 global constellation, destined to number 27 upon completion, successfully launched from Xichang on June 24. Once in final orbit and commissioned, it will become the second of three planned inclined geosynchronous orbit (IGSO) satellites, traipsing in figure-eight loops across the skies above China and neighbors in the Asia-Pacific region.

The IGSO trio will play a key role in the expansion of BeiDou-3 from a regional to a global system, in that they may afford the Asia-Pacific region greater BeiDou-derived accuracy and availability — the so-called “optimized coverage” — than will be accessible to users of the constellation in other areas of the world.

The new satellite, like others of its latest generation, will establish inter-satellite ranging links, and carries new-gun rubidium atomic clocks and passive hydrogen maser clocks. It weighs 450 kg, a gain over previous generations, with a phased array antenna for navigation signals, a laser retroreflector and deployable S/L-band and C-band antennas.

While BeiDou-3 has widespread applications in construction, transportation, fishing, power grid, disaster response, public security, smart cities and more, it will also bring increased capability — and independence from GPS — to the People’s Liberation Army. At 2 million strong with modernizing equipment, this is a force to be reckoned with in an increasingly unsettled region, with China actively pursuing numerous territorial disputes.

BeiDou-3 is migrating its civil or B1 signal from 1561.098 MHz to 1575.42 MHz, the same as the GPS L1 and Galileo E1, and changing from a quadrature phase shift keying modulation to a multiplexed binary offset carrier modulation similar to Galileos E1 and the pending GPS L1C.

June 24, 2019
K2 will drive GLONASS under 1M

New GLONASS-K2 satellites will improve the accuracy of Russia’s satellite navigation system from 3-5 meters to less than 1 meter, said Chief Designer Mikhail Korablyov of the Joint Stock Company GLONASS, operator of the ERA-GLONASS traffic accident emergency response system, at a transport conference in Moscow in late May.

Russia plans to launch the first K2 satellite in late 2019 or early 2020. By 2030 the GLONASS constellation will consist wholly of K2 space vehicles, 24 of them.

The improved accuracy will better determine vehicle location in analyzing a traffic accident, according to Korablyov. It will not, however, be sufficient for lane-keeping and other advanced driver assistance systems, nor for more stringent autonomous driving requirements, at least according to emerging Western standards.

“There are also tasks linked with the country’s defense, there are special precision weapons, the requirements for which already make up less than a meter,” Korablyov added.

Yury Urlichich, First Deputy Director General, Roscosmos. (Photo: Roscosmos)

Numbers. Writing in the December 2018 issue of GPS World, Yury Urlichich, First Deputy Director General, Roscosmos State Space Corporation, gave a somewhat more precise figure for the new accuracy to be achieved via the K2 generation. “The new signals will allow lowering the hardware-dependent SC-user ranging error by an order of magnitude, reducing the influence of signal reflections from buildings, constructions and landscape (multipath effect), thus enabling their effective use for high-precision navigation with real-time errors below 0.1 m.

“This SC will enable navigation not only using legacy FDMA signals available for users for more than 35 years, but simultaneously with a full row of CDMA signals in all GLONASS frequency bands: L1, L2 and L3.”

Later in the same piece, Urlichich wrote “Mission Definition Requirements for Glonass-K2 define user range error to be 0.3 m, qualitatively improving GLONASS user performance.”

The new K2 satellite will transmit nine navigation signals and will weigh about 1,800 kg, twice as much the latest GLONASS-K generation, known as K1. Of the 24 currently orbiting operational satellites, only two are K1 space vehicles. The other 22 are older GLONASS-M satellites.

A Shock to the System. A bolt of lightning struck the rocket launcher for the latest GLONASS-M satellite to rise, on May 27. It did not adversely affect the bird’s journey to space, and all systems were found to be functioning properly once the satellite was released into preliminary orbit, Russian space officials said.

June 20, 2019