  Magnetic field sensing provides crucial insights into various geophysical
phenomena such as atmospheric currents, crustal magnetism, and oceanic
circulation. In this paper, a method for remote detection of magnetic fields
using mesospheric sodium with an assisting satellite is proposed. Sodium atoms
in the mesosphere are optically pumped with a ground-based laser beam. A
satellite-borne detector is used to measure magneto-optical rotation of the
polarization of a probe laser beam by the sodium atoms. This sensitive
magnetometry method benefits from direct detection of laser photons and
complements existing space- and aircraft-borne techniques by probing magnetic
fields at upper-atmospheric altitudes inaccessible to those.
