I made a video that you might find interesting, titled "Spatial Resolution of Magnetometer and Gravimeter Imaging Arrays".  I talk about ways to hack existing gravimeters, seismometers, and magnetometers by adding sensors and ADCs so you can chop the incoming signal (light and gravity and magnetic fields are all coming in at the speed of light and gravity) in time, and use that to narrow down where the source event is in space.  Using networks and correlating data from many sensors, you can narrow down which specific volume element is involved.  

I did some simple calculations to clarify my ideas, using sound cards and inexpensive ADCs as examples.  I talk about localizing earthquake seismic waves, but the same considerations should apply to the magnetometer networke -- IF they can sample at high enough rates to get the spatial resolution where you can begin to image and localize magnetic events.

https://www.youtube.com/watch?v=JwNTwxgAJkM