Gradiometer
Encyclopedia
A gradiometer measures the gradient
(numerical rate of change) of a physical quantity
, such as a magnetic field or gravity.
s:
Each sensor type responds differently to certain spatial signals.
Gradient
In vector calculus, the gradient of a scalar field is a vector field that points in the direction of the greatest rate of increase of the scalar field, and whose magnitude is the greatest rate of change....
(numerical rate of change) of a physical quantity
Physical quantity
A physical quantity is a physical property of a phenomenon, body, or substance, that can be quantified by measurement.-Definition of a physical quantity:Formally, the International Vocabulary of Metrology, 3rd edition defines quantity as:...
, such as a magnetic field or gravity.
Types of gradiometer
There are at least two types of gradiometer to measure magnetic fieldMagnetic field
A magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...
s:
- Axial gradiometer. Such a device consists of two magnetometerMagnetometerA magnetometer is a measuring instrument used to measure the strength or direction of a magnetic field either produced in the laboratory or existing in nature...
s placed in series (i.e. one above the other). The result coming from the device is the difference in magnetic fluxMagnetic fluxMagnetic flux , is a measure of the amount of magnetic B field passing through a given surface . The SI unit of magnetic flux is the weber...
at that point in space (a.k.a. first spatial derivative). - Planar gradiometer. Such a 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.
See also
- Gravity gradiometryGravity GradiometryGravity gradiometry is the study and measurement of variations in theacceleration due to gravity. The gravity gradient is the spatial rate of change of gravitational acceleration....
- MagnetoencephalographyMagnetoencephalographyMagnetoencephalography is a technique for mapping brain activity by recording magnetic fields produced by electrical currents occurring naturally in the brain, using arrays of SQUIDs...
- Geophysical survey (archaeology)