Magnetometer readings are much less easy to jam than GPS signaling

Tuesday, August 25th, 2020

The U.S. Air Force is looking into using Earth’s magnetic field as an alternative to GPS:

Magnetic fields emanating from the earth’s surface vary in intensity, just like topography, and so-called magnetic anomaly maps of those fields have existed for years. Back in 2017, Aaron Canciani, an assistant professor of electrical engineering at the Air Force Institute of Technology, set out to see if magnetic sensors (magnetometers) affixed to aircraft could measure the intensity of those magnetic fields and, thus, locate the plane based on where it was in relation to those “landmarks.” His paper (and this video) shows how to outfit a Cessna plane with magnetometers in the rear and the front. Forty flight-hours worth of data and a lot of work reducing noise from the readings proved the idea viable.

But swapping magnetic fields for GPS isn’t easy. Unlike a crisp clear signal from space, factors such as the electrical operations of the plane itself can interfere with a sensor’s ability to detect the strength of the field. This is where artificial intelligence comes in, canceling out the noise from the sensor readings to allow for a better signal and more accuracy.

Researchers in the Air Force’s-MIT Artificial Intelligence Accelerator. community, working with scientists at MIT, continued to work on the problem, publishing their own paper in July. They showed that magnetic field readings can be accurate to ten meters, only slightly inferior to GPS, which is accurate down to three meters. But magnetometer readings are much less easy to jam than GPS signaling. GPS readings rely on a signal sent along a specific wavelength across vast distances. Magnometers just have to read the magnetic environment around the vehicle.


  1. Kirk says:

    This will founder on the same issues that our inertial navigation did during the Cold War. You need carefully mapped data in enemy territory to make targeting work, and if they don’t allow you to do the mapping…? Good luck making it work.

    Little-known fact about our ICBM force back before GPS: Accuracy was a joke, in the real world. When you trucked a missile to Vandenberg, overhauled it, and then put a carefully-curated guidance package into it that had been painstakingly mapped out down to the South Pacific test ranges, that did not indicate what sort of accuracy or reliability you’d see firing the damn things over the North Pole, in and out of the Van Allen radiation belts, and over terrain we did not have the gravity maps for…

    The more cynical types who knew all the ins and outs of this stuff, being as they built it? They expected that maybe ten out of a hundred US missiles might hit near their targets, and that maybe one out of a hundred Soviet missiles would hit. Just thank God we never found out the hard way, because before GPS came in, odds are excellent that the map of the strikes coming in during the opening phases of WWIII would look a lot like some drunk with a set of darts was throwing them at a map…

  2. Wang Wei Lin says:

    An EMP pulse would disable almost everything. Magnetic sensors most certainly destroyed.

  3. Kirk says:

    I’d suggest you look into that. EMP is a real thing, but it’s not the science fictional “end of the world” sort of thing it’s built up to be in popular fiction.

    It’s about like lightning strikes; weird and unexpected things happen to equipment and in the environment. The natural world is a hell of a lot more random than we would like to think, and the effect of EMP takes place in that world.

    It’s a lot like the way blast waves propagate; sure, it’s predictable and somewhat consistent, but given some “unusual” meteorology, and you’re going to see things that you’d never predict or expect.

    Friend of mine used to do EMP testing for the Navy; inside the lab, things were very consistent. They took what they did in the lab and went out into the real world to validate, and then things got very weird, very quick. Pumping that much electromagnetic energy into the environment can have some very unpredictable consequences, and we’re still babes in the woods when it comes to understanding it all.

    Pretty much everything you read where they say “Yeah, everything electronic across the country died instantly…” is bullshit. There will be some really bizarre things going on–Say that they did do an EMP strike big enough to take out a lot of the infrastructure. Odds are pretty good that there would be some really weird eddy effects created by the various local conditions and the major electrical transmission lines, and if there were another Carrington Event these days…? LOL. Seriously unpredictable in the likely effects, other than that a lot of things would be royally ‘effed up.

    Don’t buy the end-of-the-world hype. They sell it like it’ll all go down, but the reality is that we’re gonna get a ton of “unpredictable who-knew” sort of stuff.

  4. Harry Jones says:

    EMP pulse, eh? Nuke the nukes?

  5. Bruce says:

    “You need carefully mapped data in enemy territory to make targeting work”

    I’m confused. Isn’t that how TERCOM (terrain-mapping) navigation works? I didn’t think INS navigation worked that way.

  6. Kirk says:

    You want a small enough CEP to take out a missile silo with inertial guidance equipment we had prior to GPS, you need painstakingly surveyed gravity maps. For the flight path from Vandenberg to the South Pacific test ranges, that took several years to create, and they had to validate them extensively with the early test shots before they got the accuracy up to advertised standard. This was why GPS was such a big deal and why the Soviets built GLONASS for their own use. Also, why the Chinese and Europeans have built their own systems…

    TERCOM was for cruise missiles. Mostly. From the early days until GPS came in, the whole thing was a house of cards, and possibly still is, in some significant ways. The vaunted “95% hit rate” for ICBM re-entry vehicles has only really been tested (for the US) firing from north-to-south from Vandenberg to the South Pacific test ranges with carefully overhauled missiles loaded with specialized custom guidance packages and then monitored by entire teams of controllers throughout the flight. Not at all what is going to happen during a “come as you are” situation during wartime, which in and of itself is going to mean drastically different results than we’ve all been taught to expect. With modern systems, this has hopefully changed, but who knows?

    One reason that we never went nuclear during the Cold War was that nobody really knew what would actually happen. Most of the expensive tech was mostly so much BS on both sides that you couldn’t really trust much of anything. Fuck, we sold the Soviets most of the klystron switches they needed to make their bombs work, and we did that deliberately in order to give them enough confidence in their nukes that MAD could work and they wouldn’t try some other BS. The whole thing was a massive con job on the taxpayers in some very significant ways…

  7. Bruce says:

    Interesting – modern GPS weapons are described as GPS-assisted INS. Do those modern INS devices use gravity maps or does GPS negate that need (g-estimates are good enough)? In my job, i use CEP data but I do not have a GNC background.

  8. Sam J. says:

    I think ICBM’s used to use star trackers and gravity maps before GPS.

    If I remember correctly SR-71′s had star trackers for a navigation fix.

    I doubt INS needs gravity mapping. It would take the last known good GPS fix and integrate that into it’s psition.

    Before GPS we had Loran which used a master station that would send out a radio ping and then slaves would respond when they got the master ping. By measuring the time delay, you knew where the stations were, you could get a fix on your position.

  9. Kirk says:

    Pure INS needed precise gravity mapping to get the CEP down low enough to kill missile silos. We didn’t have it for the flight paths into the Soviet Union, only over Canada and the polar region we had access to.

    Whole thing was a crapshoot, really. The entire ICBM complex, including the Soviet stuff, was a house of cards that would have probably created great disappointment for all the politicians concerned. Friend of mine who was intimately involved with Minuteman guidance work confided in me that he hoped WWIII never happened, because the aftermath was going to be monumentally ugly for those “steely-eyed missilemen” and their grandiose promises. He figured that we’d be lucky to get maybe 10% of the warheads near enough to a Soviet silo to create a mission-kill on their stuff, and that if the Soviets launched, given what he knew of their classified test data that he’d had access to, you could pretty much count on North America looking like it had measles. His take on their stuff was that it might be safer to be at ground zero in the missile fields than at some random location in the US or Canada…

    This was, of course, all before GPS and the fall of the Soviet Union. When you look at the whole picture, you really start to wonder about it all, and the conventional wisdom about Star Wars systems–Say that they did manage to attrit 10% or so of the Soviet missiles: Considering the likely issues overall, that supposed “ineffective defense” might have made a huge difference in calculation for anyone planning an attack.

    Thing that’s interesting to consider, too: Effect of weather on a launch. Everyone presupposes that a launch=hit, but when you look at the actual test data from launches from Vandenberg that include weather conditions like unexpected wind during the boost phases…? Suddenly, you start to wonder about whether or not the missiles would have even gotten out of the atmosphere on the way up.

    We most definitely have a really skewed view of how effective these systems are, at least in popular imagination. The reality would likely be much different than we imagine, even today.

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