  We propose and investigate the inverse problem of identifying magnetized
anomalies beneath the Earth using the geomagnetic monitoring. Suppose a
collection of magnetized anomalies presented in the shell of the Earth. The
presence of the anomalies interrupts the magnetic field of the Earth, monitored
above the Earth. Using the difference of the magnetic fields before and after
the presence of the magnetized anomalies, we show that one can uniquely recover
the locations as well as their material parameters of the anomalies. Our study
provides a rigorous mathematical theory to the geomagnetic detection technology
that has been used in practice.
