Editing Earth's magnetic field (section)

=== Detection ===
The Earth's magnetic field strength was measured by [[Carl Friedrich Gauss]] in 1832<ref>{{cite web |author=Gauss, C.F |date=1832 |title=The Intensity of the Earth's Magnetic Force Reduced to Absolute Measurement |url=http://21stcenturysciencetech.com/translations/gaussMagnetic.pdf |access-date=2009-10-21}}</ref> and has been repeatedly measured since then, showing a relative decay of about 10% over the last 150 years.<ref>{{cite journal |journal=[[Annual Review of Earth and Planetary Sciences]] |volume=1988 |issue=16 |page=435 |title=Time Variations of the Earth's Magnetic Field: From Daily to Secular |first1=Vincent |last1=Courtillot |author1-link=Vincent Courtillot |first2=Jean Louis |last2=Le Mouel |doi=10.1146/annurev.ea.16.050188.002133 |bibcode=1988AREPS..16..389C |year=1988 }}</ref> The [[Magsat]] satellite and later satellites have used 3-axis vector magnetometers to probe the 3-D structure of the Earth's magnetic field. The later [[Ørsted (satellite)|Ørsted satellite]] allowed a comparison indicating a dynamic geodynamo in action that appears to be giving rise to an alternate pole under the Atlantic Ocean west of South Africa.<ref name="pmid11948347">{{cite journal |last1=Hulot |first1=G. |last2=Eymin |first2=C. |last3=Langlais |first3=B. |last4=Mandea |first4=M. |last5=Olsen |first5=N. |title=Small-scale structure of the geodynamo inferred from Oersted and Magsat satellite data |journal=[[Nature (journal)|Nature]] |volume=416 |issue=6881 |pages=620–623 |date=April 2002 |pmid=11948347 |doi=10.1038/416620a |bibcode=2002Natur.416..620H|s2cid=4426588 }}</ref>

Governments sometimes operate units that specialize in measurement of the Earth's magnetic field. These are geomagnetic observatories, typically part of a national [[Geological survey]], for example, the [[British Geological Survey]]'s [[Eskdalemuir Observatory]]. Such observatories can measure and forecast magnetic conditions such as magnetic storms that sometimes affect communications, electric power, and other human activities.

The [[Intermagnet|International Real-time Magnetic Observatory Network]], with over 100 interlinked geomagnetic observatories around the world, has been recording the Earth's magnetic field since 1991.

The military determines local geomagnetic field characteristics, in order to detect ''anomalies'' in the natural background that might be caused by a significant metallic object such as a submerged submarine. Typically, these [[magnetic anomaly detector]]s are flown in aircraft like the UK's [[Hawker Siddeley Nimrod|Nimrod]] or towed as an instrument or an array of instruments from surface ships.

Commercially, [[geophysical]] [[prospecting]] companies also use magnetic detectors to identify naturally occurring anomalies from [[ore]] bodies, such as the [[Kursk Magnetic Anomaly]].