Atmospheric noise
Atmospheric noise is radio noise caused by natural atmospheric processes, primarily lightning discharges in thunderstorms. On a worldwide scale, eight million lightning discharges per day — about 100 lightning flashes per second.
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[edit] History
In 1925, AT&T Bell Laboratories started investigating the sources of noise in its transatlantic radio telephone service[1].
Karl Jansky, a 22 year old researcher undertook the task. By 1930, a radio antenna for a wavelength of 14.6 meters was constructed in Holmdel, NJ, to measure the noise in all directions. Jansky recognized three sources of radio noise[2]. The first (and strongest) source was local thunderstorms. The second source was weaker noise from more distant thunderstorms. The third source was a still weaker hiss that turned out to be galactic noise from the center of the Milky Way. Jansky's research made him the father of radio astronomy[3].
[edit] Lightning
Atmospheric noise is radio noise caused by natural atmospheric processes, primarily lightning discharges in thunderstorms. It is mainly caused by cloud-to-ground flashes as the current is much stronger than for cloud-to-cloud flashes.[citation needed] On a worldwide scale, eight million lightning flashes occur daily. This is about 100 lightning flashes per second.[citation needed]
The sum of all these lightning flashes results in atmospheric noise. It can be observed[4] with a radio receiver in the form of a combination of white noise (coming from distant thunderstorms) and impulse noise (coming from a near thunderstorm). The power-sum varies with seasons and nearness of thunderstorm centers.
Although lightning has a broad-spectrum emission, its noise power increases with decreasing frequency. Therefore, at Very Low Frequency and Low frequency, atmospheric noise often dominates, while at High Frequency, man-made noise dominates in rural areas.
[edit] Survey
From 1960s to 1980s, a worldwide effort was made to measure the atmospheric noise and variations. This has been documented in the CCIR 322[5] publication. CCIR 322 provided seasonal world maps showing the expected values of the atmospheric noise figure Fa at 1 MHz during four hour blocks of the day. Another set of charts relates the Fa at 1 MHz to other frequencies. CCIR Report 322 has been superseded by ITU P.372[6] publication.
[edit] Random number generation
Atmospheric noise and variation is also used to generate high quality random numbers.[7] Random numbers have interesting applications in the security domain.[8]
[edit] See also
[edit] References
- ^ Singh (2005, pp. 402–408)
- ^ Singh (2005, pp. 404–405)
- ^ Singh (2005, p. 406)
- ^ Sample of atmospheric noise|url=http://www.ycars.org/EFRA/audio%20files/atmospheric%20noise.mp3
- ^ CCIR Report 322 Noise Variation Parameters|url=http://www.spawar.navy.mil/sti/publications/pubs/td/2813
- ^ ITU, Recommendation P.372: Radio Noise|url=http://www.itu.int/rec/R-REC-P.372/en
- ^ Haahr, Mads, Introduction to Randomness and Random Numbers, random.org, http://www.random.org/randomness/, retrieved November 14, 2011, self-published.
- ^ http://www.random.org/
- Singh, Simon (2005), Big Bang: The Origin of the Universe, Harper Perrennial, ISBN 978-0-00-716221-5
- Spaulding, Arthur D.; Washburn, James S. Washburn (April, 1985), Atmospheric Radio Noise: Worldwide Levels and Other Characteristics, NTIA Report TR-85-173, Boulder, CO: U. S. Department of Commerce, National Telecommunications & Information Administration, Institute for Telecommunications Sciences, http://www.its.bldrdoc.gov/pub/ntia-rpt/85-173/
