From Wikipedia, the free encyclopedia
Range 300-3000 Hz of the electromagnetic spectrum
Ultra low frequency
Frequency range
| 0.3 to 3
kHz
|
---|
Wavelength range
| 1,000 to 100
km
|
---|
Ultra low frequency
(
ULF
) is the
ITU
designation
[1]
for the
frequency
range of electromagnetic waves between 300
hertz
and 3 kilohertz, corresponding to wavelengths between 1,000 to 100 km. In
magnetosphere
science and
seismology
, alternative definitions are usually given, including ranges from 1 mHz to 100 Hz,
[2]
1 mHz to 1 Hz,
[3]
and 10 mHz to 10 Hz.
[4]
Many types of waves in the ULF frequency band can be observed in the
magnetosphere
and on the ground. These waves represent important physical processes in the near-Earth plasma environment. The speed of the ULF waves is often associated with the
Alfven velocity
that depends on the ambient magnetic field and plasma mass density.
This band is used for communications in
mines
, as it can penetrate the earth.
[5]
Earthquakes
[
edit
]
Some monitoring stations have reported that
earthquakes
are sometimes preceded by a spike in ULF activity. A remarkable example of this occurred before the
1989 Loma Prieta earthquake
in
California
,
[6]
although a subsequent study indicates that this was little more than a sensor malfunction.
[7]
On December 9, 2010, geoscientists announced that the
DEMETER
satellite observed a dramatic increase in ULF radio waves over
Haiti
in the month before the magnitude 7.0
M
w
2010 earthquake
.
[8]
Researchers are attempting to learn more about this correlation to find out whether this method can be used as part of an early warning system for earthquakes.
Earth mode communications
[
edit
]
ULF has been used by the military for
secure communications
through the ground. NATO
AGARD
publications from the 1960s detailed many such systems, although it is possible that the published papers left a lot unsaid about what actually was developed
secretly
for defense purposes. Communications through the ground using conduction fields is known as "Earth-Mode" communications and was first used in
World War I
.
Radio amateurs
and electronics hobbyists have used this mode for limited range communications using audio power amplifiers connected to widely spaced
electrode
pairs hammered into the soil. At the receiving end, the signal is detected as a weak
electric current
between a further pair of electrodes. Using weak signal reception methods with PC-based
DSP
filtering with extremely narrow bandwidths, it is possible to receive signals at a range of a few kilometers with a transmitting power of 10?100
W and electrode spacing of around 10?50
m.
[
citation needed
]
See also
[
edit
]
References
[
edit
]
- ^
"Rec. ITU-R V.431-7, Nomenclature of the frequency and wavelength bands used in telecommunications"
(PDF)
. ITU. Archived from
the original
(PDF)
on 31 October 2013
. Retrieved
20 February
2013
.
- ^
V. A. Pilipenko, "ULF waves on the ground and in space",
Journal of Atmospheric and Terrestrial Physics
, Volume 52, Issue 12, December 1990, pp. 1193?1209,
ISSN
0021-9169
,
doi
:
10.1016/0021-9169(90)90087-4
.
- ^
T. Bosinger and S. L. Shalimov, "On ULF Signatures of Lightning Discharges",
Space Science Reviews
, Volume 137, Issue 1, pp. 521?532, June 2008,
doi
:
10.1007/s11214-008-9333-4
.
- ^
O. Molchanov, A. Schekotov, E. Fedorov, G. Belyaev, and E. Gordeev, "
Preseismic ULF electromagnetic effect from observation at Kamchatka
",
Natural Hazards and Earth System
Sciences, Volume 3, pp. 203?209, 2003
- ^
HF and Lower Frequency Radiation - Introduction
Archived
2005-11-09 at the
Wayback Machine
- ^
Fraser-Smith, Antony C.; Bernardi, A.; McGill, P. R.; Ladd, M. E.; Helliwell, R. A.; Villard, Jr., O. G. (August 1990).
"Low-Frequency Magnetic Field Measurements Near the Epicenter of the M
s
7.1 Loma Prieta Earthquake"
(PDF)
.
Geophysical Research Letters
.
17
(9): 1465?1468.
Bibcode
:
1990GeoRL..17.1465F
.
doi
:
10.1029/GL017i009p01465
.
ISSN
0094-8276
.
OCLC
1795290
. Retrieved
December 18,
2010
.
- ^
Thomas, J. N.; Love, J. J.; Johnston, M. J. S. (April 2009). "On the reported magnetic precursor of the 1989 Loma Prieta earthquake".
Physics of the Earth and Planetary Interiors
.
173
(3?4): 207?215.
Bibcode
:
2009PEPI..173..207T
.
doi
:
10.1016/j.pepi.2008.11.014
.
- ^
KentuckyFC (December 9, 2010).
"Spacecraft Saw ULF Radio Emissions over Haiti before January Quake"
.
Cambridge
,
Massachusetts
:
MIT Technology Review
. Retrieved
December 18,
2010
.
External articles
[
edit
]
|
---|
ELF
3 Hz/100 Mm
30 Hz/10 Mm
|
SLF
30 Hz/10 Mm
300 Hz/1 Mm
|
ULF
300 Hz/1 Mm
3 kHz/100 km
|
VLF
3 kHz/100 km
30 kHz/10 km
|
LF
30 kHz/10 km
300 kHz/1 km
|
MF
300 kHz/1 km
3 MHz/100 m
|
HF
3 MHz/100 m
30 MHz/10 m
|
VHF
30 MHz/10 m
300 MHz/1 m
|
UHF
300 MHz/1 m
3 GHz/100 mm
|
SHF
3 GHz/100 mm
30 GHz/10 mm
|
EHF
30 GHz/10 mm
300 GHz/1 mm
|
THF
300 GHz/1 mm
3 THz/0.1 mm
|
|
|