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Magnetometer
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===Performance and capabilities=== The performance and capabilities of magnetometers are described through their technical specifications. Major specifications include<ref name=Macintyre2000/><ref name=Hovde2013/> *''Sample rate'' is the number of readings given per second. The inverse is the ''cycle time'' in seconds per reading. Sample rate is important in mobile magnetometers; the sample rate and the vehicle speed determine the distance between measurements. *''Bandwidth'' or ''bandpass'' characterizes how well a magnetometer tracks rapid changes in magnetic field. For magnetometers with no onboard [[signal processing]], bandwidth is determined by the [[Nyquist limit]] set by sample rate. Modern magnetometers may perform smoothing or averaging over sequential samples, achieving a lower noise in exchange for lower bandwidth. *''Resolution'' is the smallest change in a magnetic field the magnetometer can resolve. A magnetometer should have a resolution a good deal smaller than the smallest change one wishes to observe. This includes [[quantization error]] which is caused by recording roundoff and truncation of digital expressions of the data. *''Absolute error'' is the difference between the readings of a magnetometer true magnetic field. *''Drift'' is the change in absolute error over time. *''Thermal stability'' is the dependence of the measurement on temperature. It is given as a temperature coefficient in units of nT per degree Celsius. *''Noise'' is the random fluctuations generated by the magnetometer sensor or electronics. Noise is given in units of <math>\rm{nT}/\sqrt{\rm{Hz}}</math>, where frequency component refers to the bandwidth. *''Sensitivity'' is the larger of the noise or the resolution. *''Heading error'' is the change in the measurement due to a change in orientation of the instrument in a constant magnetic field. *The ''dead zone'' is the angular region of magnetometer orientation in which the instrument produces poor or no measurements. All optically pumped, proton-free precession, and Overhauser magnetometers experience some dead zone effects. *''Gradient tolerance'' is the ability of a magnetometer to obtain a reliable measurement in the presence of a magnetic field [[gradient]]. In surveys of [[unexploded ordnance]] or landfills, gradients can be large.
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