During the geomagnetic storm that took place May 10–11, 2024, GPS users reported significant positioning errors and outages. In particular, farmers in the Central United States reported difficulty in getting a fix with their tractors and other farm equipment.
Also affected, to a lesser extent, was the Southwestern United States.
A new study has identified the cause of the GPS outages by analyzing the data from a 1‐Hz GPS receiver network. Standalone GPS position errors In precise point positioning (PPP) mode in the Central United States reached 70 meters on May 10. The errors were attributed to a steep wall in ionospheric plasma that rapidly moved southward.
In the soutwestern states, the GPS position errors were elevated 10 to 20 meters because of the enhanced plasma density.
Vertical protection level as provided by WAAS.
Then, on May 11, intense auroral activity caused rapid enhancements in the ionospheric plasma, leading to abrupt position errors of 10 meters. Network‐based position systems likely encountered even longer duration of position errors because these ionospheric disturbances are localized.
“These findings highlight the need for more accurate understanding of ionospheric plasma conditions, as well as software and hardware improvements, to reduce disruptions during space weather events,” report the authors of “Spatio‐Temporal Evolution of Mid‐Latitude GPS Scintillation and Position Errors During the May 2024 Solar Storm.” Authors are Waqar Younas, Yukitoshi Nishimura , Weixuan Liao , Josh L. Semeter, Sebastijan Mrak, Jade Morton and Keith M. Groves. The full report will appear in an upcoming issue of the Journal of Geophysical Research: Space Physics and is now available on ResearchGate.
Figure 2. Phase scintillation index over the United States during the geomagnetic storm at 22:00 UT on May 10, 2024. The map is derived from the Global Positioning System (GPS) signals. The map shows enhanced phase fluctuations that impacted GPS position accuracy. Adapted from Figure 4d of the paper. (Credit: Authors)
Key Points
PPP failed to converge in the SED and trough, while PPK became unstable after CME arrival until the recovery phase.
SED, EIA, and trough created position errors on the noon‐evening sector. Substorms caused position errors on the nightside.
Scintillation, cycle slips, satellite geometry and ray bending were identified as contributing factors to the large position errors.
Figure 3. GPS position error over the United States during the geomagnetic storm at 22:00 UT on May 10, 2024. The map is derived from the Global Positioning System (GPS) signals. The map shows large error occurs at trough boundary and enhanced TEC regions. Adapted from Figure 5d of the paper. (Credit: Authors)
The study investigates impacts of the May 2024 superstorm on the mid‐latitude GPS scintillation and position errors. Using 1‐Hz GPS receiver data, the research team identified position errors in PPP mode reaching up to 70 m in the Central United States during the storm main phase on May 10.
The PPK solution becomes unstable following the arrival of storm and lasted till the recovery phase, coinciding with reported GPS outages of farming equipment. The large position errors were attributed to strong scintillation and carrier phase cycle slips around the equator-ward boundary of the ionosphere trough, where large total electron content (TEC) gradients and irregularities were present.
In the Southwestern United States, position errors of 10–20 m were associated with the storm‐enhanced density and equatorial ionization anomaly. Scintillation and cycle slips in this region were minor, and bending of the GPS signal paths (refractive effect) is the probable cause of the position errors. PPP outages were also associated with sudden changes in the geometric distributions of available GPS satellites used in position calculations.
On May 11, energetic particle precipitation during substorms led to abrupt jumps in TEC and scintillation, resulting in rapidly evolving position errors of up to 10 m. These findings highlight the critical role of storm‐time plasma transport, precipitation and irregularity formation in degrading GPS performance.
“The study underscores the need for accurate ionospheric state specification, improved signal processing technique, real‐time ionospheric corrections, and optimized satellite selection algorithms to enhance navigation resilience during severe space weather events,” the authors conclude.
Jackson Labs Technologies PNT-6200 Series, an STL-based time and frequency reference system installed in a 5G application. Photo: Satelles
We discussed Satellite Time and Location (STL) services and complementary PNT with Michael O’Connor, CEO at Satelles.
What is the problem with GPS/GNSS that Satelles aims to solve?
GPS and GNSS are amazing. We designed Satellite Time and Location (STL), the service that we offer, to complement those capabilities. We have focused on three unique aspects in the areas where GPS could use complementary service. First, we provide a fully independent backup. We all know that things can happen, so we aim to provide an independent source of position navigation, and timing (PNT). Second, we focused the high-power aspect of STL to enable us to reach indoors and other places where GPS does not reach. Because STL comes from low Earth orbit (LEO) satellites, the signals are naturally at a higher power.
We also focused on improving the indoor penetration capability by enhancing the signal design and doing some other things. Third, we use modern cryptographic techniques to ensure the security and resilience of the system, specifically to intentional misdirection attacks. If you can ensure that the signal is coming from the satellite and not from a third party you can have a more secure and resilient solution.
To what extent can you replace GPS during an extended outage?
We have never considered LEO PNT as a replacement for MEO (medium Earth orbit) GNSS. GNSS are the primary domain of PNT but there are applications that have additional needs. The more independence you can get, the fewer the common modes of failure, if you can at least have some survivability in the absence of GNSS. That’s one of the services we can offer. It is probably not the most important thing to our customers, honestly. The service we offer is similar to GPS and GNSS in that we have a space segment (the satellites), a ground segment, and a user segment. We have space vehicles, user equipment, and ground infrastructure that supports the space infrastructure.
What’s interesting about the way we work with the Iridium satellite constellation is that the satellites themselves include inter-satellite links. That provides a lot of resilience to ground-based events. The satellites themselves have a time transfer capability between them. So, we don’t require a direct connection to every satellite to propagate a time throughout the network. That’s one unique aspect we can take advantage of with this particular network, Iridium, which is pretty amazing.
Additionally, we have multiple ground infrastructure and monitoring sites and multiple sources of time at those ground monitoring and control stations. For example, some of them rely on GNSS combined with atomic clocks as their master timing source but we also have one installed at the National Institute of Standards and Technology facility in Boulder, Colorado. So, we have multiple primary time sources that we can integrate into our filtering across the network. That, combined, with satellite links, allows us to maintain time for substantial periods independent of GNSS.
How do you define “complementary PNT” and how does Satelles fit in that mix?
Several applications have additional needs beyond what GNSS offer. There are many technologies that can come to bear on that. There’s the LEO satellite base, which is where Satelles fits in, but there are also local and wide-area terrestrial radio navigation sources, network-based time transfer, signals of opportunity, and so on. They all have something important to offer, depending on the application. Satelles’ LEO satellite solution is available today, has global coverage, and is relatively affordable. It leverages the capital investments that have been made to launch the satellites to provide this service globally. The industry is working together to make sure that an awareness of these capabilities is propagated throughout the industries that we serve.
Besides the orbit height, which requires many more satellites, how does your system differ from GNSS?
We do not consider LEO PNT as something that might replace MEO PNT. The fundamental difference is being in lower Earth orbit, which results in a higher received power. That is what allows us to penetrate, just based on the 1/r2 losses. The measurable Doppler signatures give additional observables for PNT calculations, and higher satellite dynamics that can help with multipath. This service relies on many of the same physics and geometry as GPS. We measure the time of arrival of a very similar signal. The signals from the Iridium satellites are even in the L band. Very often we’re using a GPS chip that’s been reprogrammed to track and utilize our service as well as GPS or instead of GPS.
If I explained how GPS works to, say, a high school science class, how much of that basic explanation—about trilateration, spread spectrum, etc.—would also apply to your system?
It’s fundamentally the same. It relies on a lot of the same physics and geometry. We measure the time of arrival of a very similar signal. The signals from the Iridium satellites are even in the L band. Very often we’re using a GPS chip that’s been reprogrammed to track and utilize our service as well as GPS or instead of GPS. There are subtle differences—for example, a lower Earth orbit is faster—but it is very similar.
How would GPS user equipment have to be modified to make use of your service?
We don’t think of STL as something where we are modifying GPS user equipment. Rather, we think about what must be done in an end-user application to meet their needs. For example, one of our partners, Orolia, has a GNSS + STL secure synchronization product that we have delivered to customers in data centers and major stock exchanges around the world. Those are operational and in service. They integrate through standard interfaces, such as PPS or PTP, depending on the type of equipment to which they are connecting.
Ultimately, we don’t think of it is as replacing GPS user equipment. Rather, where a user has a need for PNT, they’re opting for this GNSS + STL solution because they have an indoor need, such as a data center, or they have a need for resilience in the case of a stock exchange.
Another example is Jackson Labs. The Jackson Labs 2600 is also a GNSS + STL solution that generally is integrating with existing 5g. It has a specialized transcoder interface that can work with any existing GNSS-type equipment. In some cases, we’ve taken a chip that was originally designed for GPS and modified its firmware.
Who are the earliest adopters?
Satelles’ LEO satellite solution is available today, has global coverage, and is relatively affordable. It leverages the capital investments that have been made to launch the satellites to provide this service globally. Data centers, stock exchanges and cell phone providers are implementing these capabilities today. The major wireless operators are seeing that more and more of the 5G infrastructure they roll out is going indoors, where GPS doesn’t reach. We provide a solution that integrates with their existing solutions and can provide reliable timing capabilities.
If your solution can survive on its own, why does it need GNSS at all?
In some cases, the user is not using GNSS at all. The product itself has a GNSS capability. User equipment is very affordable and the service is taxpayer-funded. In many cases, especially for indoor installations, the equipment that is installed is capable of tracking GNSS and STL signals, but often it relies on the STL signal itself for timing.
How do you predict STL spreading through various applications and industries?
We have our hands full with the markets we’re going after now, but there are certainly going to be other markets in which the customers will recognize that they have a critical need to implement a backup solution.
In the long run, could LEO satellites replace MEO ones for GNSS?
Sometimes there have been misperceptions in the industry. I’ve never considered that LEO PNT satellites might replace MEO ones. There are excellent reasons why Brad Parkinson, Jim Spilker, Gaylord Green and others decided almost 50 years ago to put GPS in MEO. Those physics haven’t changed. You can cover a large portion of Earth with each satellite. LEO will not replace MEO, but it has unique characteristics that make it a great complement to the GNSS MEO solutions.
Do you have any additional comments about complementary PNT?
It’s good to see that the federal government is encouraging the adoption of complementary PNT, which they often call “GPS backup.” It is encouraging to see the amount of activity on this issue that’s been going in Washington over the last couple of years. Although our company is very focused on delivering a LEO-based PNT service, which has several advantages for customers that need a global capability, many technologies can play an important role in those solutions.
The U.S. Department of Transportation did a fantastic job of looking at several of those technologies across those different categories. The European Union has also had a similar activity recently. Some reports will be coming out soon about that. It is very important that the government understands that this is an important issue for our society and encourages industry to adopt these solutions and is even starting to make some investments toward that. That includes executive order 13905 and some recent funding increases by Congress.
All of that has been very important and positive, as has modifying some of the legislation to be more inclusive of multiple technologies, such as removing the words “land-based” from the National Timing, Resilience, and Security Act this year.
I am involved in an industry consortium, the Open PNT Industry Alliance, with several other companies whose CEOs are in alignment that there is no single answer. Having a thriving ecosystem of technologies and companies trying to solve this important problem is incredibly important and it’s exciting to see.
Oceanographic & Geophysical Instruments (OGI) has selected iXblue’s Atlans INS to provide robust and uninterrupted data georeferencing to its newly unveiled mobile-mapping lidar solution dedicated to road assessment surveys.
A fully integrated mobile mapping solution, this new vehicle-based system integrates advanced systems to provide highly detailed georeferenced survey data to transportation departments throughout the United States.
“Highly accurate and reliable georeferencing of the collected data being crucial for road assessment operations, we were seeking a compact and robust navigation solution for our mobile scanner project,” said Darren Moss, program manager at OGI. “We tested other inertial navigation systems (INS) during mobile surveys in New York City and Boston with poor results, as those INS units relied mainly on GPS signals. Maintaining good GPS signals in the urban canyons of large cities proved to be impossible. This deeply impacted the georeferencing of the acquired lidar data, leading to highly inefficient operations. This is the reason we turned to iXblue’s Atlans A7 INS.”
Based on fiber-optic gyroscope (FOG) technology, the Atlans A7 north-seeking INS offers highly accurate and robust data georeferencing. Resistant to GPS outages, it enables continuous acquisition operations within environments lacking continuous GPS signals. The Atlans A7 is a valuable system for high-accuracy data acquisition without interruption.
“Working with iXblue in other markets, we were familiar with the high-quality instrumentation they are known for. We were confident their FOG-based INS systems would perform even during GPS outages,” Darren said. “By choosing the Atlans A7, we are assured to get robust and uninterrupted georeferenced data in urban environments, tunnels, forests, and mountainous areas, which is crucial for our customer’s operations. With this INS, iXblue brings high-end FOG performance to the mobile-mapping industry at a very affordable price.”
“The Atlans A7 integrates very well within our new mobile lidar solution and, combined with Teledyne Optech Polaris high-resolution lidar scanner and QPS Qinsy display and acquisition software, it brings high-accuracy and efficiency to the core of our Mobile lidar solution,” Darren said.
