Magnetic Gradiometers

A magnetometer measures magnetic field strength at a specific measuring point. In some applications, it is more useful to measure how much the strength of a magnetic field changes between two specific points. For such a measurement of the change in field (the "gradient" of the field), a Magnetic Gradiometer is the ideal instrument.

A common application of a gradiometer is the location of features or objects that are invisible to the eye, but have magnetic properties; underground features are a typical example. The features magnetic characteristics will cause a disturbance in the earth's magnetic field in an area around the object. This disturbance can be detected as a magnetic field gradient, by a gradiometer.

Single-axis gradiometers measure magnetic gradient in a single vector-direction. They are  quick to setup, lower cost than the three-axis equivalent,  and produce data that is straightforward to analyse. Three-axis gradiometer measure the gradient in the x,y and z directions and can yield more information about features, but data processing is significantly more complicated.

Bartington Instruments produce single-axis and three-axis fluxgate gradiometers.
Click on the links below for more details of the instruments:

Grad601 Single-axis Magnetic Gradiometer
The Grad 601 is a single-axis, vertical component, fluxgate gradiometer with data logger and either one or two cylindrical sensor assemblies for use in geophysics and archaeology. Each sensor assembly contains two fluxgate magnetometers with a one metre vertical separation  together with electronics and non-volatile memory for calibration data. The system provides an enhanced depth response, exceptional stability and electronic adjustment.
Individual sensors can be supplied independently and integrated in multi-sensors instruments.

Grad-03-500L Three-axis Gradiometer
The Grad-03-500L is a three-axis gradiometer, and is an ideal choice for applications which require magnetic measurements from two closely-spaced three-axis sensors. This type of differential measurement is especially useful for magnetic detection techniques.

Grad-03-500M Three-axis Marine Gradiometer
The Grad-03-500M is a marine version of the three-axis gradiometer. The gradiometer is intended for ROV mounting and operation to a depth of 5000 metres. Applications include detection and geophysical surveys.