Both analogue and digital variometers require temperature-controlledĮnvironments and installation on extremely stable platforms (though The pick-up coil outputs a signal not only with the excitation frequencyīut also other harmonics related to the intensity of the external fieldĬomponent. Is a component of the external magnetic field along the fluxgate element, If an alternating current isįed into the excitation coil so that saturation occurs and if there Around the core there are two windings:Īn excitation coil and a pick-up coil. A fluxgate sensor comprises a core of easily saturable In the case of photographic systems or electrical voltage in the case The first category comprises variometers which makeĬontinuous measurements of elements of the geomagnetic field vectorīut in arbitrary units, for example millimetres of photographic paper There are two main categories of instrumentsĪt an observatory. The earliest magnetic observatories where continuous vector observations Must be magnetically clean and remain so for the foreseeable future. Minute or less, over a long period of time. Recorded accurately and continuously, with a time resolution of one Where absolute vector observations of the Earth's magnetic field are Other units likely toīe encountered are the Gauss (1 Gauss = 100,000 nT), the gamma (1 gammaīack to the top of the page 2.2 Observatories Varies from 22,000 nanotesla (nT) to 67,000 nT. At the Earth's surface the total intensity Of magnetic field intensity, strictly flux density, most commonly used The International System of Units (SI) unit Declination, inclinationĪnd total intensity can be computed from the orthogonal components using Magnetic variation) D (the horizontal angle between true northĪnd the field vector, measured positive eastwards). Inclination (or dip) I (the angle between the horizontal planeĪnd the field vector, measured positive downwards) and declination (or Is described by the orthogonal components X (northerly intensity), Y (easterly intensity) and Z (vertical intensity, positiveĭownwards) total intensity F horizontal intensity H First ofĪll, however, methods of observing the magnetic field are described.īack to the top of the page 2 Geomagnetic field observations 2.1 Definitions The final section describes how the Earth's magneticįield can be both a tool and a hazard to the modern world. Order low frequency to high frequency variations, in both the spaceĪnd time domains. Of scales and a description of these variations is now made, in the Observable at the Earth's surface has sources in the crust and in the In addition to sources in the Earth's core the magnetic field ElectricalĬurrents flowing in the slowly moving molten iron generate the magneticįield. In the fluid outer core by a self-exciting dynamo process. 2 Geomagnetic field observations 2.1 Definitions 2.2 Observatories 2.3 Satellites 2.4 Other direct observations 2.5 Indirect observationsģ Characteristics of the Earth's magnetic field 3.1 Reversals 3.2 The present magnetic field 3.3 Westward drift 3.4 Geomagnetic jerks 3.5 Crustal magnetic field 3.6 Field variations at quiet times 3.7 Field variations at disturbed timesĤ The Earth's magnetic field as both a tool and a hazard in the modern world 4.1 Navigation 4.2 Directional drilling 4.3 Geomagnetically induced currents 4.4 Satellite operations 4.5 Exploration geophysics