Underground Localization in 3-D Using Magneto-Inductive Tracking

Localization of mobile devices underground is extremely challenging, with radio propagation (such as used in GPS and VHF) severely attenuated by soil and moisture. However, low frequency magnetic fields are able to penetrate the ground with minimal loss. Mobile underground tracking devices record magnetic field strengths generated by an array of transmitting coils placed above the area of interest. This information is stored in flash memory, for opportunistic upload over a conventional radio link when the device is above ground. As a particular application of this technology, the underground movements of wild European badgers (Meles meles) were tracked in 3-D within their burrow systems, by equipping them with lightweight tracking collars. Typical localization accuracy is 0.45 m RMS over a 15 m × 15 m area and collar lifetime is of the order of 9 months from a 1.4 Ah lithium cell.