A gradiometer measures the
gradient
In vector calculus, the gradient of a scalar-valued differentiable function f of several variables is the vector field (or vector-valued function) \nabla f whose value at a point p gives the direction and the rate of fastest increase. The g ...
(numerical rate of change) of a
physical quantity
A physical quantity (or simply quantity) is a property of a material or system that can be Quantification (science), quantified by measurement. A physical quantity can be expressed as a ''value'', which is the algebraic multiplication of a ''nu ...
, such as a magnetic field or gravity.
Types of gradiometer
There are at least two types of gradiometer to measure
magnetic field
A magnetic field (sometimes called B-field) is a physical field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular ...
s:
# ''Axial gradiometer''. This device consists of two
magnetometer
A magnetometer is a device that measures magnetic field or magnetic dipole moment. Different types of magnetometers measure the direction, strength, or relative change of a magnetic field at a particular location. A compass is one such device, ...
s placed in series (i.e., one above the other). The result coming from the device is the difference in
magnetic flux at that point in space, in other words, the result is the difference between what each of the magnetometers detects.
# ''Biaxial gradiometer''. This device consists of three magnetometers measuring the gradient of the magnetic field in two directions.
# ''Triaxial gradiometer''. This device consists of four magnetometers measuring the gradient of the magnetic field in three directions.
# ''Planar gradiometer''. This device consists of two magnetometers placed next to each other. The result coming from the device is the difference in flux between the two loops.
Each sensor type responds differently to certain spatial signals.
Axial gradiometers are good for measuring depth, while planar gradiometers can measure weak signals even under a lot of noise.
See also
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Gravity gradiometry
Gravity gradiometry is the study of variations (gravitational anomaly, ''anomalies'') in the Earth's gravity field via measurements of the spatial gradient of gravitational acceleration. The gravity gradient tensor is a 3x3 tensor; it is given in ...
*
Magnetoencephalography
Magnetoencephalography (MEG) is a functional neuroimaging technique for mapping brain activity by recording magnetic fields produced by electric current, electrical currents occurring naturally in the human brain, brain, using very sensitive magn ...
*
Geophysical survey (archaeology)
References
Measuring instruments
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