The National Geospatial-Intelligence Agency is looking for people to find novel approaches to gathering and utilizing magnetic data in conjunction with their development and support of the World Magnetic Model (WMM).  They rely heavily on ths European Space Agency "Swarm" of satellites to measure and calibrate the World Magnetic Model.  But they would like to use sensor data fusion to improve and verify the space-based sensor network.  So anything is fair game.

Personally I think they should at least upgrade the existing magnetic networks with decent ADCs, continous high sensitivity monitoring arrays, and get their Internet data sharing down to current practices at least.

https://www.magquest.com/

Here is what they say about the WMM:  "The WMM is embedded in thousands of systems. More than a billion smartphone users depend on the WMM to point them in the right direction when they use mobile navigation apps. Drivers rely on the WMM to power the compasses in their cars.  The WMM is also critical for military and commercial uses around the world. Among other applications, it supports navigation and attitude determination for submarines, satellites, and aircraft, while also informing operational logistics like the numbering of runways."

So they have an existing user base, but are not collecting ground truth from them apparently.  If you could hack the cell phone to provide ground truth, or plug millions of low cost sensors into Internet so they can be used to constrain the solutions when they try to build their model, it will help them with their current plans.  And, presumeably pay for you to continue to help them.

But it might be that there are other ways to provide better solutions to the fundamental problems and needs of their clients.  Perhaps there are better ways to solve for orientation and location using existing GPS, or by upgrading selected cell phones.  Or by letting people put in local nodes to provide very precise updates on magnetic field variations.  I can think of about 30 things to try. But, my main concern is they also upgrade sampling rates so whatever sensors are created or upgraded, can be used for magnetic time of flight imaging arrays.