A plurality of magnetic field sensors, for example arranged in an array, is operative to measure changes in magnetic field strength proximate the surface(s) of a test structure. The test structure may approximate the geometry of an airplane fuselage, wing, or the like. An electric current is applied to the test structure, and the magnetic field sensors sense changes in a magnetic field caused by the current. A corresponding plurality of integrators convert the sensor outputs to magnetic field strength values. From the plurality of magnetic field strength values and corresponding sensor locations, a current density over the target surface is inferred.