A
gradiometer for measuring properties of a
magnetic field and in particular, for measuring
magnetic field gradient components, comprising at least two magnetic sensors wherein at least two of the magnetic sensors are arranged to sense the
magnetic field component in substantially the same direction. The magnetic sensors may be super conducting
quantum interference device (
SQUID) magnetometers, Hall probes, flux gates or
magneto-resistive magnetometers. The
gradiometer also includes a computer processor loaded with an adaptive
signal-
processing algorithm, for performing adaptive
signal balancing of the
magnetometer outputs. In a preferred embodiment the
gradiometer may comprise at least eight magnetometers in a three-dimensional arrangement, and a set of three orthogonal global feedback coils, one for each direction x, y, z, such that the five independent
magnetic field gradient components may be measured. The gradiometer may also be used to measure second or higher order
magnetic field gradient components.