A Distributed Magnetometer Network
  Various possiblities for a distributed magnetometer network are considered. We discuss strategies such as croudsourcing smartphone magnetometer data, the use of trees as magnetometers, and performing interferometry using magnetometer arrays to synthesize the magnetometers into a large-scale low-frequency radio telescope. Geophysical and other applications of such a network are discussed. 
John Scoville, John Spritzer, and Friedemann Freund
physics.geo-ph astro-ph.IM physics.pop-ph