Mapping the Earth’s magnetic field
BERKELEY, Calif. – Current astronomy technology could be used to more accurately measure the Earth’s magnetic field,
physicists have found. This development could prove useful in tracking storms, finding
oil and minerals, or studying the planet’s interior.
A group of scientists from the University of California has discovered
a more effective way to measure the Earth’s magnetic field using ground-based
lasers rather than satellites. They found that the same sodium atoms in the atmosphere
used in laser guide stars – artificial stars used as a reference point to
adjust telescope optics to remove atmospheric disturbances – could be employed
to measure the Earth’s magnetic field. The findings appear in Proceedings
of the National Academy of Sciences, March 1, 2011 (doi: 10.1073/pnas.1013641108).
The new method involves emitting an orange beam from a ground-based
laser into the mesosphere, located about 90 km above the Earth’s surface,
where there is a 10-km-thick layer of sodium atoms. The beam from the laser, which
is small enough to load onto a truck or boat, is used to measure the rotation frequency
of the sodium atoms, which are used as sensors to measure the strength of the Earth’s
To measure the Earth’s magnetic field, an orange laser beam is directed at a
layer of sodium 90 km above the Earth. The beam is pulsed at a rate determined by
the local magnetic field to excite spin polarization of the sodium atoms, producing
a fluorescence emission. This is detected by a ground-based telescope and analyzed
to determine the strength of the magnetic field. Courtesy of Dmitry Budker lab,
Less expensive than a satellite system, this method could lead
to other ground-based laser techniques. It allows scientists to take measurements
without the spatial and temporal dependence associated with satellite movement.
Satellites used currently to measure the Earth’s magnetic
field are moving at high speeds, so it is not always possible to tell whether fluctuations
are actual or a result of the spacecraft’s movement to a new location. In
addition, metals and electronic instruments aboard the satellite could affect magnetic
field measurements. Ground-based remote sensing systems, on the other hand, eliminate
Creating maps of the Earth’s magnetic field is important
for geology, studies of currents in the atmosphere and oceans, climatology, and
oil and mineral exploration. The group will continue its studies of how spin-polarized
sodium atoms emit and absorb light, and it is building a 20-W modulated laser for
the Very Large Telescope in Chile to test its theories.
- The scientific observation of celestial radiation that has reached the vicinity of Earth, and the interpretation of these observations to determine the characteristics of the extraterrestrial bodies and phenomena that have emitted the radiation.
- remote sensing
- Technique that utilizes electromagnetic energy to detect and quantify information about an object that is not in contact with the sensing apparatus.
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