Mätfokus - Maetfokus

GPS III Space Vehicle 06 (SV06) reached Operational Acceptance on Jan. 31 according to the Space Systems Command (SSC) of the United States Space Force. SV06 was launched on a SpaceX Falcon 9 Block 5 vehicle on Jan. 18.

SSC also transferred Satellite Control Authority (SCA) of SV06 to the 2nd Space Operations Squadron at Schriever Space Force Base, Colorado. GPS III SV06 joins the GPS PNT constellation of 31 operational satellites.

This is the first time SCA and Operational Acceptance has occurred on the same day enabling faster delivery for users. SSC’s Military and Communication positioning, navigation and timing (PNT) enterprise collaborated with the U.S. government acquisition team, industry and space operators on the achievement.

“The Operational Acceptance of GPS III SV06 further contributes to SSC’s ongoing modernization efforts, as it brings our overall suite of capabilities ever closer to our target dates for deployment to the warfighter,” said Col. Heather J. Anderson, transition director within SSC’s PNT directorate. “GPS III SV06 will be set healthy to all global users in February 2023.”

The first-stage booster used in the SV06 launch previously sent the NASA Crew-5 mission to the International Space Station on Oct. 5, 2022.

Military Communications and PNT is SSC’s program executive office responsible for delivering next-generation technologies, which bolster the resilience of military satellite communications and space based PNT capabilities. Innovation focus areas include strategic, protected tactical, wideband and narrowband satellite communications, GPS user equipment and command and

Read Richard Langley’s introduction column, Innovation Insights: What is a carrier phase?

---

An approach for ground vehicles using carrier-phase and inertial measurement data

By Zachary Clements, James E. Yonder and Todd E. Humphreys

The combination of easily accessible low-cost GNSS spoofers and the emergence of increasingly automated GNSS-reliant ground vehicles prompts a need for fast and reliable GNSS spoofing detection. To underscore this point, Regulus Cyber, an Israeli cybersecurity company, recently spoofed a Tesla Model 3 on autopilot mode, causing the vehicle to suddenly slow and unexpectedly veer off the main road.

Among GNSS signal authentication techniques, signal-quality monitoring (SQM) and multi-antenna could be considered for implementation on ground vehicles. However, SQM tends to perform poorly on dynamic platforms in urban areas where strong multipath and in-band noise are common, and multi-antenna spoofing detection techniques, while effective, are disfavored by automotive manufacturers seeking to reduce vehicle cost and aerodynamic drag. Thus, there is a need for a single-antenna GNSS spoofing detection technique that performs well on ground vehicles, despite the adverse signal-propagation conditions in an urban environment.

In a concurrent trend, increasingly automated ground vehicles demand ever-stricter lateral positioning to ensure safety of operation. An influential study calls for lateral positioning better than 20 centimeters on freeways and better than 10 centimeters on local streets (both at a 95% probability level). Such stringent requirements can be met by referencing lidar and camera measurements to a local high-definition map, but poor weather (heavy rain, dense fog or snowy whiteout) can render this technique unavailable.

On the other hand, progress in precise (decimeter-level) GNSS-based ground vehicle positioning, which is impervious to poor weather, has demonstrated surprisingly high (above 97%) solution availability in urban areas. This technique is based on carrier-phase differential GNSS (CDGNSS) positioning, which exploits GNSS carrier-phase measurements having millimeter-level precision but integer-wavelength ambiguities.

Key to our promising results is the tight coupling of CDGNSS and inertial measurement unit (IMU) data, without which high-accuracy CDGNSS solution availability is significantly reduced due to pervasive signal blockage and multipath in urban areas. Tight coupling brings millimeter-precise GNSS carrier-phase measurements into correspondence with high-sensitivity and high-frequency inertial sensing. Our particular estimation architecture incorporates inertial sensing via model replacement, in which the estimator’s propagation step relies on bias-compensated acceleration and angular rate measurements from the IMU instead of a vehicle dynamics model.

As a consequence, at each measurement update, an a priori antenna position is available whose delta from the previous measurement update accounts for all vehicle motion sensed by the IMU, including small-amplitude high-frequency motion caused by road irregularities. Remarkably, when tracking authentic GNSS signals in a clean (open-sky) environment, the GNSS carrier-phase predicted by the a priori antenna position and the actual measured carrier phase agree to within millimeters.

The research described in this article pursues a novel GNSS spoofing-detection technique based on a simple but consequential observation: it is practically impossible for a spoofer to create a false ensemble of GNSS signals whose carrier-phase variations, when received through the antenna of a target ground vehicle, track the phase values predicted by inertial sensing. In other words, antenna motion caused by factors such as road irregularities or rapid braking or steering is sensed with high fidelity by an onboard IMU but is unpredictable at the sub-centimeter-level by a would-be spoofer.

Therefore, the differences between IMU-predicted and measured carrier-phase values offer the basis for an exquisitely sensitive GNSS spoofing-detection statistic. What is more, such carrier-phase fixed-ambiguity residual cost is generated as a byproduct of tightly coupled inertial-CDGNSS vehicle position estimation.

Two difficulties complicate the use of fixed-ambiguity residual cost for spoofing detection. First is the integer-ambiguous nature of the carrier-phase measurement, which causes the post-integer-fix residual cost to equal not the difference between the measured and predicted carrier phases (as would be the case for a typical residual), but rather modulo an integer number of carrier wavelengths. Such integer folding complicates development of a probability distribution for a detection test statistic based on carrier-phase fixed-ambiguity residual cost.

Second, the severe signal multipath conditions in urban areas create thick tails in any detection statistic based on carrier-phase measurements. Setting a detection threshold high enough to avoid false spoofing alarms caused by mere multipath could render the detection test insensitive to dangerous forms of spoofing. Reducing false alarms by accurately modeling the effect of a particular urban multipath environment on the detection statistic would be a Sisyphean undertaking, requiring exceptionally accurate up-to-date 3D models of the urban landscape, including materials properties.

Our work takes an empirical approach to these difficulties. It does not attempt to develop a theoretical model to delineate the effects of integer folding or multipath on its proposed carrier-phase fixed-ambiguity residual cost-based detection statistic. Rather, it develops null-hypothesis empirical distributions for the statistic in both shallow and deep urban areas, and uses these distributions to demonstrate that high-sensitivity spoofing detection is possible despite integer folding and urban multipath.

WHAT IS CARRIER PHASE? The obvious answer is: the phase of the carrier. But this is not helpful if you don’t know what a carrier is. A carrier is basically a harmonic electromagnetic wave — a pure continuous sinusoidal wave with a single constant frequency and amplitude.

Such a wave has limited uses. However, if we modulate or change the characteristics of the wave in some way, then the wave can carry information. Changing the amplitude by using a voice or music audio signal is amplitude modulation as used for AM radio.

Instead, one could modulate a carrier by changing its instantaneous frequency, which is frequency modulation or FM and is used for high-fidelity broadcasting. Yet another way to modulate a carrier is to change the instantaneous phase of the carrier, and that is how GNSS works.

GNSS carriers are phase-modulated by pseudorandom noise (PRN) codes and navigation messages. A GNSS receiver uses the PRN codes to produce the pseudorange observable with a precision in the tens of decimeter range. This is the most common observable for GNSS positioning.

But by stripping away the modulation of the received GNSS signals, the receiver can measure the phase of the underlying carrier. Changes in carrier phase over time reflect the change in the (pseudo)range but are about two orders of magnitude more precise.

One problem with carrier-phase measurements is that they have an initial cycle ambiguity that must be resolved, preferentially fixed to the correct integer value, before they can be used for positioning, but this can be achieved without too much difficulty. While fixing the ambiguity of carrier-phase measurements might be considered a nuisance in GNSS positioning, it can help detect spoofing of GNSS signals where some other techniques might fall short.

In this “Innovation” column, we look at how carrier-phase measurements combined with those from an inertial measurement unit can guard against a deliberate attack on an automated ground vehicle — something that cannot be discounted in our world these days.

Read the full “Innovation” column: GNSS Spoofing Detection: Guard against automated ground vehicle attacks.

Surveying is both an ancient profession and one of today’s most technologically advanced. Surveyors are among the first on the site of a new construction project, staking out its corners and boundaries, and mapping elevation contours, as well as among the last, surveying the project “as built.” This is particularly important for features that will no longer be visible once the project is complete, such as underground utilities.

While many surveyors work in quiet, uncrowded environments — such as surveying the boundaries of farm fields — those who work on large construction projects operate among the hustle and bustle of bricklayers, carpenters, electricians, plumbers and other tradespeople, as well as cranes, backhoes and other heavy machines. This chaotic environment means that in addition to accuracy and efficiency, surveyors also are concerned with safety.

In the following cover story, a Minnesota-based construction company describes a new system it developed for surveying and mapping underground utilities. Also, professional surveyor Gavin Schrock discusses the benefits of a flexible approach to GNSS rover accuracy and of adding scanning capabilities to robotic total stations.

Read the three parts of this cover story: 

1. Minnesota company develops new system for mapping underground utilities new pipes
2. Review benefits of GNSS rover accuracy
3. Robotic total stations add scanning capabilities

GMV is using high-resolution optical imagery as a part of emergency management efforts, to map the population and infrastructure of several cities in Turkiye after the 7.8 magnitude earthquake. The imagery of the aftermath is thanks to Europe’s Copernicus program, which keeps satellites and Earth observation services operational to support management and decision-making in different areas, particularly in the field of emergency management.

GMV is one of the suppliers of Copernicus program infrastructure. GMV monitors the database architecture and ensures its integrity, analyzes the data required by the service chains, and identifies the most suitable technologies to keep the entire program operational.

GMV is working with the EU Civil Protection Mechanism’s Emergency Response Coordination Center to keep them updated on the ongoing emergency situation.

For more on the emergency satellite mapping, visit the Copernicus website.

Maxar Technologies shared via Twitter satellite imagery from the aftermath of the train derailment and explosion in East Palestine, Ohio. The train derailed on Feb. 3 and was carrying toxic materials.

The satellite images show the ongoing cleanup efforts following the derailment. The wrecked train can be clearly seen as well as blue storage containers being used to collect hazardous materials.

Hundreds of East Palestine residents had to evacuate their homes after a Norfolk Southern Railroad train carrying vinyl chloride derailed and exploded, emitting deadly fumes into the air and toxic material into the Ohio River.

A Feb. 8 press release from Ohio Governor Mike Dewine stated that it was safe for residents to safely return to their homes. “There will be ongoing air monitoring in the area, but for those who would like air quality readings to be conducted within their homes, Norfolk Southern Railroad has hired an independent contractor to work with local law enforcement, the U.S. EPA, and state officials to take air quality samples and provide results at no charge to residents,” it said.

New #satellite imagery from today, February 15, 2023, showing the aftermath of the recent freight train #derailment that occurred on February 3 in #EastPalestine, #Ohio. Imagery reveals an extensive cleanup operations in progress, and blue material storage containers nearby. pic.twitter.com/B1xvhM0ETJ

— Maxar Technologies (@Maxar) February 15, 2023

This is part III of our III part cover story. Catch up on part I, Minnesota company develops new system for mapping underground utilities and part II, Review benefits of GNSS rover accuracy.

---

Scanning capabilities, in one form or another, have been added to models of robotic total station (RTS) since 2007 — for instance, on the Trimble VX. Such capabilities were limited to a pattern of individual shots, as the RTS would “nod.” While not designed to compete with traditional scanners, even such painfully slow “pseudo-scanning” capabilities demonstrate the value of new options for capturing detailed features.

It was not long before nearly all RTS offered limited (nodding scanning) capabilities, though at rates as slow as 15 shots per second. By 2013, the release of the Leica MS50 took the nodding scan to the next level, with a rate of up to 1,000 points per second, and then up to 30,000 in the subsequent MS60 model (which now also supports a tilting prism pole).

The end of 2016 saw the release of Trimble’s SX10 (and SX12 more recently). This routed the laser through a pair of rotating prisms to capture a swath of points as it nodded. In 2019, Topcon took the approach of adding a piggy-backed compact conventional scanner to the top of an RTS: the GTL-1000 and GTL-1200 models.

All these implementations were built upon high-quality RTS. Foremost, they can be operated as an RTS, with all the same integrated surveying capabilities as instruments with which surveyors were familiar, and in the same field software.

This includes all the integrated GNSS workflows: resections, combining optical and GNSS captured points in the same survey, and adding a rover to the prism pole for track-on-GNSS methods. One huge advantage of scanning total stations is instant deliverables already fully registered, as adopters of these new systems quickly realized.

Some initial users seemed skeptical of the relatively slow scan rates of these various models: 12 to 30 minutes for full-dome scans, and then a photo capture pass. Others, though, discovered that the time did not necessarily need to go to waste.

First, it is not necessary to do a full-dome scan and image pass every time; it is sufficient to pre-select specific areas to scan and image.

The real kicker is that while the RTS is scanning, it is possible to fire up the GNSS rover and capture points that the RTS cannot see, such as behind curbs, cars and vegetation. This is true especially now, with the advent of no-compensation tilt capabilities on nearly every new GNSS rover system.

This can be done in the same project, using the same software and field controller. This struck this writer as one of the coolest lateral features of scanning total stations when he first tried out an SX10 in 2017.

Considering the benefits scanning total stations deliver (especially with the integrated GNSS bonus), what has the reception been like among surveyors and other segments of the architecture, engineering and construction (AEC) community?

“As an industry, we’re getting better at tying solutions and workflow elements together, and not seeing them, or treating them, as individual functions or pieces of hardware,” said Derek Shanks, director of Geospatial Optical Product Management for Trimble. “We bring the system aspect, a case of using the best tool, using the strengths of each tool to their fullest.”

Accoring to multiple manufacturers, sales numbers indicate that the adoption of scanning total stations for AEC applications — and not just surveying — has exceeded expectations.

This is part II of our III part feature story. Check out part I, Minnesota company develops new system for mapping underground utilities and part III, Robotic total stations add scanning capabilities.

---

High precision GNSS rovers play a vital role in a broad variety of field surveying and mapping applications. Different users have different value propositions in mind when choosing field hardware and software: expected precision, sources of corrections, configurations for specific workflows, and, of course, cost. Weighing these many considerations, GNSS manufacturers have come up with portfolios of multiple models to fill these varied needs.

That said, GNSS manufacturer Bad Elf took a different approach when it designed its flagship rover, the Bad Elf Flex. The Flex is designed to meet the cost-precision-workflow needs of everyone, from asset mappers to surveyors. (Hence the name “Flex.”) To inform the design of the Flex, Bad Elf listened to field users who wished for a scalable solution in a single rover, rather than having to buy multiple different models, and without breaking the bank.

Options for the Infrequent User

“I had one of the little Bad Elf GNSS surveyor handhelds for many years,” said Jason Schilling, wildlife biologist with Douglas County Public Utility District in central Washington State. “That worked great for rough mapping, between a foot and a meter of precision, and I could connect it via Bluetooth to mapping software on my mobile.”

But this all changed when Schilling began an unmanned aerial system (UAS) program for the utility several years ago.

“I really needed survey-level precision for ground control points to geolocate the images from the UAS,” said Schilling.

He was aware of the high cost of centimeter-precision-capable surveying rovers and it was too big of an investment, considering that he only did UAS mapping a few times a month. As an existing Bad Elf customer on the company mailing list, Schilling learned about the new Flex rover, which offered multiple options, and he found one that seemed quite enticing for the needs of his utility.

Schilling purchased a Flex Standard bundle at a low base price, about $3,000, with the pay-as-you-go plan for high precision. In the standard configuration, the Flex is capable of autonomous positioning (1–5 m), and mapping grade (sub-meter precisions) via free satellite-based augmentation services (SBAS), such as WAAS. But when the user activates a pre-purchased “token,” the full centimeter-precision capability, using external corrections, is enabled.

“On the day of a UAS survey, we turn it on, activate a token from our account, and then we have 24 hours of high precision,” Schilling said. “It costs us $25 per day.”

For two to three UAS surveys a month, this works out to far less over many years than the cost of buying a typical surveying rover.

Correction Sources

For real-time kinematic (RTK) corrections, Schilling connects via NTRIP to the statewide cooperative real-time network (RTN); sometimes in a network RTK mode (such as VRS) or single-base RTK to a nearby reference station on the same network. The Flex accommodates NTRIP connections to RTN or IP-enabled reference stations, but Bad Elf has added even more flexibility for corrections.

In some scenarios there is no access to an RTN or no cell service (needed for NTRIP access). One option in these cases is to add a second Flex, set it up as an RTK base, and connect the base and rover via radios that Bad Elf offers.

Bad Elf has added other options for corrections: the Bad Elf RTK service taps into a nationwide real-time network operated by Point One Navigation. This is accessible via NTRIP in the same manner as regional, state or local RTN, and is offered for a monthly fee. In addition, for situations where there is no RTN or cell service, a global precise point positioning (PPP) service (Atlas) can be enabled on the Flex.

PPP differs from RTK/RTN in that it does not need the dense arrays of reference stations, or cell service to access. Instead, PPP derives very precise clock and orbit data from a global array of tracking stations and delivers this to the Flex via geostationary satellites. After a short convergence time, PPP from the Atlas service will yield 5 –10 cm precision over most of the globe.

The Full Boat

The City of Ellensburg, a college town and farming community in central Washington State, chose the Flex Extreme bundle for about $6,000 — the “full boat” configuration. The Extreme bundle enables all the add-on services all the time, eliminating the need for tokens. In their case, the frequency of use made the higher initial investment worthwhile.

“We have big plans for our rovers,” said Brian Cortese, Engineering Tech/Inspector for the City of Ellensburg Public Works & Utilities.

Ellensburg is a vibrant town that is attracting a lot of new development and it is being proactive in surveying and mapping assets as they are added or replaced.

“We’re recording manholes and valves, sewer systems, storm water systems, irrigation, hydrants — everything that gets built in the city gets as-built surveyed,” Cortese said. “Precise, real-time positioning, it’s been a benefit to us already. We can go out before they work on the subgrade for new developments and take measurements, and then when they finish the subgrade and pave it, we can go back and locate those exact positions.”

Ellensburg uses corrections from the statewide cooperative RTN. In fact, one of the RTN reference stations —also part of the NOAA National CORS Network — is right in the center of town atop the science building of Central Washington University. While the city does a wide variety of surveying and mapping, with the Flex and RTN corrections surveyors get the same centimeter-precision for everything they measure in the field.

“We’ve done design projects with it,” Cortese said. “For instance, we recently took measurements in an area of downtown for a proposal by recording positions and elevations to develop a new park and entertainment area for the community. We are also marking Americans with Disabilities Act (ADA) ramps to meet federal specs out in the field — it’s been really handy for so many things.”

Survey-Grade Rover

To serve the full range of precision needs, the Flex had to be designed as a survey-grade rover. It has a full-constellation GNSS and RTK engine: GPS, GLONASS, Galileo, BeiDou, and support for other regional constellations. With more satellites in view, it can perform in sky-view-challenged locations, such as around buildings and under tree canopy.

“Ellensburg is on the Tree City, USA list; our streets are very well lined with a variety of trees, which is also where a lot of our utilities are and development is going on,” Cortese said. “We have been able to get good precisions in and around those trees. Actually, someone on our staff is taking an inventory of the trees with the Flex and loading the data directly into ArcGIS.”

Even in the more rural areas of Grant County that enjoy a lot of open sky, Schilling said, some areas planned for mapping are along upper tributaries and in the hills with a lot of tree coverage. He said the Flex has performed well in those areas.

Choices

The Flex offers these options and combinations:

• Flex Extreme. Full survey-grade rover that can use a variety of correction types.
• Base-Rover RTK. Two Flex Extreme units connected via radio.
• External RTN/RTK corrections via NTRIP.
• Bad Elf RTK Service. Single-tap access to a nationwide RTK corrections service.
• PPP service. Atlas PPP corrections via L-band geostationary satellites.
• Flex Standard. Pay-as-you-go high-precision-enabled service using tokens.
• Static Logging. Observation file logging for post-processing (supported by Flex Extreme).
• Compatibility with multiple field-mapping software applications.

While many modern GNSS rover systems support one or more options similar to those listed above, Bad Elf’s Flex supports all of them, making it capable of a wide variety of applications.

This is part I of our III part feature story. Read more in part II, Review benefits of GNSS rover accuracy  and part III, Robotic total stations add scanning capabilities.

---

The danger of hitting a buried water or gas pipe when digging for a construction project persists despite many efforts to reduce it, such as “call before you dig” phone numbers. For example, in Minnesota there were 4,000 such hits in 2019. That is one reason why it is very important to map “as built” underground utilities accurately. This must be done quickly and efficiently, before trenches are filled and without slowing progress of the project.

Traditionally, crews have mapped the underground pipes and cables on paper. In turn, when a construction project needs to know the location of underground utilities before digging, it typically relies on someone who consults those paper maps, uses an electromagnetic utility locating tool, and marks the ground with spray paint. The construction crew then must correctly interpret those marks on the ground. In 2019, Minnesota-based utility consultancy Ellingson Companies was asked to develop a new and more efficient process.

Capturing Data in Real Time

By leveraging solutions from Esri and from Canadian hardware and software manufacturer Eos Positioning Systems, Ellingson Companies GIS Manager Damon Nelton developed a solution that allows his team to capture new pipe construction in real time. By streamlining documentation workflows, the new process improved field productivity and allowed Ellingson Companies to produce digital as-builts that meet the needs of its gas utility clients and improve the safety of future construction projects.

While construction crews have been putting pipe in the ground for generations, today they are expected to produce a digital record of their work in real time — for the sake of safety and efficiency.

Using Esri’s Utility Pipeline Data Model, Nelton created a system that enables crews to map their as-built pipe projects while also tracking components. The system improves data integrity — in other words, reduces human error — by relying on scannable 16-digit alphanumeric bar codes developed by the American Society for Testing and Materials that provide seven attributes for each conduit, including thickness, diameter, lot number and manufacturer date. To collect and store these data, Nelton set up an ArcGIS Enterprise geodatabase.

Gas meters, which also need to be mapped, are often in locations that are hard to map directly with a GNSS receiver because line-of-sight to the satellites is obstructed by trees, roof eves, or adjacent buildings. Therefore, they must be shot with an offset. For these situations, Nelton used Eos Positioning Systems’ laser mapping solution, which enables surveyors to use lasers attached to their range poles to feed data directly into their GIS.

No More Battleship

Using Eos Positioning System’s Arrow Gold receiver and the MNCoors RTK network, Nelton said, his team was able to average an accuracy of 0.25 throughout a project in the city of Owatonna, Minnesota, as confirmed by spot checks with other survey equipment and with the city’s survey team.

“Not every shot was easy, and some took multiple attempts and tricks of the trade to get them,” Nelton pointed out.

On projects in the middle of mountains, where real-time kinematic (RTK) networks do not exist, the company has used the Atlas Service, averaging accuracies of 12 in.

“Given the circumstances of these projects,” Nelton said, “we still consider that to be great.”

Using the new system, foremen use a survey in ArcGIS Survey123 to input their inspection notes and other information, feeding it all from the field to the office and into layers shared between divisions. This way, the data are available in real time, not at the end of the project.

For customers who still want a piece of paper to file in a physical folder in a filing cabinet, Nelton creates a Microsoft Word document template in their format, populates it using dynamic text with syntax in ArcGIS Pro, inserts a map, then saves the Word document as a PDF.

“At the end of the project, we got almost 17,000 digits with no human entry other than pressing the button on the barcode scanner, which means zero data errors,” said Nelton.

No pieces of paper with critical data on the underground utilities languish in a glove compartment or are eaten by a surveyor’s dog, and all the data is available in real time.

Additionally, the combination of the barcode scanning workflow and the high accuracy GNSS receiver enables Nelton’s team to locate gas asset pieces that need to be replaced — for example, due to a recall by the manufacturer — “without playing battleship,” he said.

Quectel Wireless Solutions’ LC76G GNSS module has been named a Product of the Year by Electronic Products. The annual awards recognize products that represent a significant advancement in technology or its application, an exceptionally innovative design, a substantial achievement in price/performance, improvements in design performance, and a potential for new product designs/opportunities. 

The LC76G module is a compact, single-band, ultra-low power GNSS module that features fast and accurate location performance. The module can concurrently receive and process signals from all satellite constellations including GPS, GLONASS, BeiDou, Galileo and QZSS. 

The LC76G has an internal surface acoustic wave (SAW) filter and integrated low-noise amplifier (LNA), which can be connected directly to a passive patch antenna and provides filtering against unwanted interference. With a compact size of 10.1 mm × 9.7 mm × 2.4 mm, the footprint of the LC76G is compatible with other industry solutions, as well as Quectel’s legacy L76 and L76-LB modules. 

The LC67G is designed for battery-operated, ultra-low power GNSS devices, such as wearable personal trackers, wildlife and livestock tracking, toll tags, portable container trackers, as well as several traditional markets such as shared mobility and low-cost asset trackers.