This work describes the development of magnetic sensing schemes to characterize corrosion of metals in situ. GMR magnetic field sensors are applied to overcome difficulties encountered with traditional corrosion detection methods without damaging the structure. Active and passive magnetic sensing configurations are presented. Passive measurements rely on very near-surface magnetic field measurements. Active magnetic tests rely on the interaction of imposed magnetic fields with corrosion-generated magnetic fields. Although active tests may be carried out at a larger offset ...