How stable is the earth's magnetic field at that level of detail? There's enough movement of the magnetic poles right now that new compass correction charts have to be issued every year or so. Will you need to constantly update your magnetic maps?
Magnetic navigation is totally real and seems to work great.
Diamond magnetometers might not be a great fit for this application. They require a powerful laser, RF, and are presently huge and impractical. Also, they are just terrible at accuracy and drift like crazy. Finally - and this is the thing I really can't get - they require a giant magnetic field to operate. If your magnetometer has a giant magnet bolted to it, you would expect it to basically measure drift in that magnet. Diamond magnetometer people will jump out of the woodwork now, but I haven't seen published high quality data that says otherwise. Would love to be proved wrong.
Diamond magnetometers are great at being a magnetic microscope since they have really high density of measurement sites and you can stick it right up next to an object of interest.
Drifting like crazy might not be such an issue if one is looking for an AC signal, such as could be produced by 130m x 13m metal objects moving against the stationary background.
Huge and impractical sounds like SQuIDs might still be preferable. LN2 is a byproduct, so it's cheap.
Field strength pretty quickly drops of over distance, and even the most powerful magnets don't go much beyond 100T (and even that's a stretch). Assuming you could somehow achieve 100T 1m away from the magnet (which is charitable, usually the high teslas are only achieved at the exact centre) then just a kilometre away it will have dropped to 1 microtesla, well below the 25~65 microtesla of the Earths gravitational field.
So you'd need those kinds of magnets on a kilometre spaced grid, which doesn't seem realistic. And that's with some rather charitable assumptions about building a strong magnet, to be honest I expect you'd have difficulty turning a few compasses in the same building, let alone miles away.
The AFRL press release linked in another comment says that this technique relies on measurement of the crustal magnetic field, which is in the 10s of nanoteslas range.
It depends on how far away they are. Magnetic (dipole) fields fall as the cube of distance. Since the earth's pole has a dipole moment (8.0 * 1022 Am^2) and is detectable ~30uT at the earth's radius, thousands of km from the core. Even a 1T field at a radius of 1m would be billion times smaller ~1nT a km away or 1/30k of the earth's field.
A giant 6T MRI would be comparable to earth's field at 27m.
They could using a small EMP weapon. These happen to have short range and are explosively pumped, so at that point it’s easier to just disrupt the magnetometer by initiating rapid explosive disassembly.
Based purely in my layman understanding of magnetism, you’d need quite a disturbance and that same energy would likely not make the rest of any electronics happy.
> so accurate that it might supersede GPS for aerial navigation
Very cool! I wonder if:
1. the device can be made small enough for consumer use (i.e., phones, smart watches, etc)
2. how much data it needs to pinpoint its location. i.e., it might be suitable in aviation because it can collect a larger amount of data by virtue of... you know... goin' fast.
1. No, anyway, your phone would have to be engineered to be non-magnetic to the same level that you wish to make measurements.
2. Yes, faster is better. Flying lower is also more specific if you have a sufficiently good magnetic map.
How do compasses work on aircraft? Don't the (varying across space/time?) magnetic fields from everything on the aircraft overwhelm whatever tiny variation there is from Earth's surface?
Compasses used in vehicles need to be calibrated to null the magnetic mass of the vehicle. This is true for airplanes and ships but also cars, although cheap car compasses often settle for poor accuracy to avoid this hassle. This whole issue is why the compass in airplanes is usually mounted in an odd place like above the glare shield or below the roof, so that it's farther from the other instruments to make the magnetic field situation simpler.
One of the earliest methods to do this has the amusing nickname of "Nelson's Balls," the binnacle (compass holder) on ships often has two large metal spheres mounted on its sides that serve to compensate for the fore-aft magnetic mass of the all the hardware in the ship.
The magnetic compass in an airplane is subject to a certain amount of variance due to installation (essentially calibration error), but that error should be quite small. More problematically, airplanes move fast enough that the magnetic compass shows errors due to the math of magnetic flux when you're moving relative to a magnetic field. The theory is somewhat complicated but pilots often remember it with acronyms like "ANDS" for accelerate north/decelerate south - basically, if there's any appreciable east-west component of your flight path, when you accelerate your compass will turn towards the north, and when you decelerate it will turn towards the south.
This is why airplanes are equipped with a heading indicator, also called a directional gyro, which uses a gyroscope to simulate a compass. The heading indicator isn't subject to the weird moving errors that the magnetic compass shows so it's more useful for maneuvering. On the other hand, the gyro does slowly drift over time, so every once in a while it needs to be reset against the magnetic compass - during straight and level flight to avoid moving errors.
A compass and a gyroscope are two very different devices.
The former measures the Earth magnetic field, which is an external magnitude independent of your craft or movement.
The later measures your rate of rotation, which is an internal magnitude. Even the best gyro will have an small amount of noise and drift, so you need some external reference to periodically correct it. Also, because they measure an speed, to get your orientation you need to integrate the measures over time, which amplifies the noise.
In reality you usually combine both with an accelerometer and a GPS.
I.. guess? Didn't even occur to me... I thought it went without saying that my comment wasn't just blatantly irrelevant to the article, but maybe I shouldn't have assumed that.
If this is basically comparing readings to a map of the Earth's magnetic field, couldn’t they use lidar and a lidar topo map? (I think cruise missiles used some type of map for navigation too).
Lidar's range is measured in hundreds of meters. That might be a bit limiting for flight. Radar could be used, but you might not want to have a "hey all, I'm here!"-beacon for military purposes.
You could of course use cameras, pointing either up (stellar navigation) or down, but that's not going to work all the time.
So while there is not such thing as a magnetic laser, there is a laser that can create a strong magnetic field.
https://physicsworld.com/a/radiation-friction-could-make-hug....