Tag: magnetic navigation

Reading the Room’s Magnetic Personality

New algorithm cuts indoor positioning error by nearly half

Conventional indoor positioning often depends on expensive Wi-Fi or Bluetooth infrastructure, or on inertial sensors that accumulate drift within seconds. Magnetic navigation has emerged as a promising alternative because steel structures and electronics leave buildings with unique, location-specific magnetic signatures.

However, existing map-free methods rely on polynomial models that oversimplify the magnetic field’s spatial variations. They capture the broad trend but miss the sharp, local anomalies caused by metal pipes or distribution boxes.

With these limitations, a more accurate, robust, and physically interpretable approach to magnetic field modeling is urgently needed for practical indoor navigation.

A team from the Aerospace Information Research Institute, Chinese Academy of Sciences, publishing (DOI: 10.1186/s43020-026-00201-3) in the journal Satellite Navigation on June 5, has unveiled a robust magnetic-inertial odometry (MIO) method based on the Fibonacci sphere-sampled equivalent magnetic dipole model, denoted as FSS-EMD-MIO. The system uses an array of 30 small magnetometers and an inertial measurement unit to track movement without any external signals.

The core innovation lies in how the system models the indoor magnetic environment. Instead of drawing smooth curves through the data, it represents the local field as a combination of virtual “equivalent magnetic dipoles” — with 16 dipoles identified as optimal through systematic parameter analysis.

Their positions are determined by the Fibonacci sphere sampling technique, which evenly distributes points in 3D space without any directional bias, preventing overfitting. Each dipole’s magnetic moment is then solved in real time using least squares fitting.

The team also derived the spatial gradient of this model, creating a direct mathematical link between changing magnetic readings and the carrier’s displacement, velocity, and attitude. To handle the inherent nonlinearity and location-dependent noise, an adaptive error state Kalman filter fuses inertial data with magnetic observations. Tested on a public dataset, the method achieved a horizontal positioning root mean square error below 1.27 meters, outperforming the previous state of the art (MAINS) by 46% on average.

“The old polynomial methods look at the magnetic field from far away — they see the hills but not the potholes. Our model places virtual sources exactly where the magnetic perturbations live,” the authors explained. “The Fibonacci sphere sampling ensures that no direction is favored, so whether you tilt the sensor or walk in circles, the system adapts reliably. We essentially gave the building’s chaotic magnetic field a readable 3D structure. This means first responders or warehouse robots can finally have a ‘magnetic compass’ that works even when the lights are off and GNSS is out.”

The research paves the way for truly infrastructure-free indoor navigation. Potential applications include guiding firefighters through smoke-filled buildings, tracking inventory robots in steel-racked warehouses, and providing positioning for autonomous vehicles in parking garages or mines. The authors note that future work will incorporate loop-closure detection to correct long-term drift, akin to how a person recognizes a familiar intersection.

By developing scan-matching algorithms based on overlapping magnetic field regions, the team aims to build a complete magnetic simultaneous localization and mapping (SLAM) system for multi-floor buildings, further closing the gap between outdoor and indoor navigation reliability.

June 18, 2026
Magnetic Navigation 2022 – Freedom from GNSS?

Dana Goward, President, Resilient PNT Foundation

In a world where GPS and other GNSS signals can be easily denied or, worse, spoofed, interest in other forms of navigation has rebounded.

Imagine being able to locate yourself within a couple of centimeters with just your cellphone – deep underground. Or inside a metal structure. Or underwater (assuming you can keep your equipment dry).

No satellite signals, no Wi-Fi ranging, no inertial system. Just the ambient magnetic flux that constantly surrounds us all. Everywhere.

That’s the vision AstraNav Vice President Martin Neill offered to the President’s National Space-based, Positioning, Navigation, and Timing Advisory Board in May.

Animals have used the Earth’s magnetic field to find their way for millions of years. People have been using magnetic compasses for over a thousand. Until the advent of GPS, magnetic compasses were foundational tools for aircraft and ship navigation, especially when out of sight of easily recognized landmarks.

Then GPS came along, and almost everyone’s eyes turned to space.

But in a world where GPS and other GNSS signals can be easily denied or, worse, spoofed, interest in other forms of navigation has rebounded. And because GPS helped demonstrate the efficiencies geospatial services provide, users also want those services to be more resilient and to work in places signals from space just can’t reach.

According to Neill, “Our solution builds upon inexpensive magnetometers, smartphones, machine learning, edge computing, and some incredibly complex math to convert raw magnetic data into a source of ultra-precise location data. These relatively recent tech developments allow us to bring things together for a major update to a centuries-old way of navigation and positioning.”

Describing AstraNav as a software tech company, Neill said that the company’s system is “hardware agnostic.” It can work on “just about anything that has a magnetometer. No additional hardware or external connectivity is required, and we can run on any existing operating system.”

Image: Credit: Petrovich9/iStock/Getty Images Plus/Getty Images

The company has partners in retail, automotive and telecom validating the technology. They have also been working with a U.S. Department of Defense (DOD) combatant commander to demonstrate the product, as well as Virginia Tech and its National Security Institute (VTNSI.) “This is not a case of ‘here’s an idea that we hope will materialize,” said Neill. Describing two real-world trials and use cases to the board, he said, “This technology is a reality, and we’re doing it.”

Most previous magnetic navigation efforts relied upon relatively low-resolution maps. An airplane could find its way safely across the ocean using the maps that were available and likely end up within a mile or two of an airport. Much higher resolution maps built through surveys and artificial intelligence are critical to AstraNav’s centimeter-level accuracy with systems that continue to learn on their own.

Intellectual property is AstraNav’s biggest asset. “We have multiple patents filed and pending,” said Neill. “Our IP is what allows us to sense and analyze magnetic fields so finely, develop maps, and make use of very low-cost magnetometers, such as the ones in cell phones.”

Several people at the advisory board presentation expressed surprise that they had not heard of the company and this capability before. “We have been busy getting established as a company, supporting our first commercial clients, and doing demonstrations for various folks within DOD,” Neill explained. “This presentation is by way of our coming out party. We are very eager to become better known and are looking forward to explaining our capabilities one-on-one with potential users.”

Citing an abundance of proprietary material, Neill was unwilling to discuss a lot of technical detail at the public meeting. His short presentation, he said, was to raise awareness and stimulate interest.

The number of those in attendance who after the presentation said they were eager to learn more showed that he was successful.

Dana A. Goward is President of the Resilient Navigation and Timing Foundation

June 9, 2022
Riding Earth’s magnetism: An alternative approach to PNT

There are many ways to navigate. For most applications, none surpass the accuracy, affordability and convenience of satellite navigation.

However, given the threats to GNSS from spoofing and jamming, and the possibility that GNSS satellites could be destroyed accidentally by space debris or intentionally during a war, the search is on for alternative sources of positioning, navigation and timing (PNT) data.

Potential alternative PNT (APNT) approaches include computer vision, terrain contour matching (TERCOM, which was used to guide cruise missiles in the 1970s and 1980s), and using magnetic anomalies (MAGNAV).

Diverse animals — such as sea turtles, spiny lobsters, and birds — use magnetoreception for orientation and navigation. However, while animals likely perform wayfinding using the direction of the magnetic field, similarly to how humans use a compass, high-resolution maps used in conjunction with atomic instruments enable us to perform absolute positioning to tens of meters, explained Major Aaron Canciani.

Canciani, an assistant professor of electrical engineering at the Air Force Institute of Technology, has been designing algorithms for MAGNAV flight testing for several years.

Earth’s crustal magnetic field varies from location to location as much as topographic features do and, like them, it changes very little over time. However, unlike topographic features, which only occur on the third of the planet’s surface covered by land, magnetic variations also occur on the oceans. This makes them potentially very useful as landmarks to the Navy and Air Force. Magnetic variations have the additional benefit that they cannot be jammed or spoofed.

NOAA’s EMAG2 World Digital Magnetic Anomaly Map. (Image: NOAA National Geophysical Data Center)

Just like other features of Earth, magnetic fields can be mapped, using scalar magnetometer sensors to measure their strength and direction. In fact, government agencies and mining companies have been making these maps for many decades, for geological exploration and other purposes, though mostly on land.

Conversely, these maps can be used to navigate by comparing the data from magnetometers to the map, just like cruise missiles used to use on-board radar altimeters to match the contours of the land beneath them to contour lines on a digital map and navigators on vessels in shallow waters compare the depths reported by their fathometers to those marked on a chart.

Before this approach to navigation can be widely implemented, however, magnetic maps need to greatly improve in coverage and quality. In addition to magnetic maps and sensors, MAGNAV also requires sophisticated algorithms and careful calibration, to do such things as subtract errors from space weather and the local magnetic field of the aircraft or ship.

The greater the platform’s speed, the greater MAGNAV’s accuracy, because the magnetometers can collect more varying magnetic information per unit of time of INS drift, Canciani explains. On a platform moving fast and at low altitudes, MAGNAV could achieve 10-meter accuracy. In less ideal conditions and relying on lower quality magnetic maps, the accuracy could be as low as one kilometer — which is sufficient for many missions, such as navigating ships at sea.

Off-the-shelf scalar magnetometers about the size of a quarter have already been flight tested. Corporations, the military and civilian government agencies such as NOAA, NASA and NGA already have suitable magnetic maps, though they need to be improved and expanded, particularly at sea. This would require gathering new data using calibrated sensors on airplanes, ships and submarines.

Could magnetic sensors be installed on thousands of aircraft, land vehicles and sea vessels to collect magnetic data during their routine operations? “With proper calibration, yes, but it should not be downplayed how difficult it is to get 1 nanoTesla measurements on a platform,” Canciani said. “Mapping and navigation are inverse problems so any platform that has been calibrated well enough to navigate could, in turn, also be used for mapping.”

However, he points out, the task is much more complicated than just putting a magnetometer on a platform. “Getting clean data on complex platforms remains the largest challenge for magnetic navigation,” Canciani said, “although we are making excellent progress with projects like the Air Force Accelerated AI program with MIT and Lincoln Lab. In this project we are using state of the art scientific machine learning approaches to calibrate complex magnetic fields on operational platforms. Without excellent calibration algorithms the only sure-fire way to get clean magnetic data is putting a sensor out on a boom or wing-tip, which might not be practical for all use cases.”

Two F-16 Fighting Falcons fly over Edwards AFB during a 2009 air show. (Photo: U.S. Air Force/Chad Bellay)

Canciani admits that MAGNAV is often met with skepticism but hopes that realistic testing on realistic platforms will lead to more interest and funding for this approach.

While some such testing has already been performed using private survey aircraft, a much more important test will take place in September, when F-16s from the Air Force Test Pilots School will fly MAGNAV sensors and software over a test range next to Edwards Air Force Base in Nevada.

July 20, 2020