An even brighter meteor burst over Main Street in May 2004.
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Although only about 28 meters in diameter, the meteor burst released about 210 kilotons of energy, equivalent to about 220 of the atomic bombs dropped on Hiroshima, shattering glass in nearby buildings in the city of Chelyabinsk, and causing dozens of minor injuries from the fallout.
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Earth–Moon–Earth communication, Meteor burst communications, and Sporadic E propagation are also other methods of achieving communications past the radio horizon.
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Meteor scatter propagation as used by SNOTEL Meteor burst communications (MBC), also referred to as meteor scatter communications,Weitzen, J.A. Meteor scatter communication: A new understanding. In Meteor Burst Communications. Wiley, New York, 1993, 9–58. is a radio propagation mode that exploits the ionized trails of meteors during atmospheric entry to establish brief communications paths between radio stations up to apart.
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Such ionization trails can last up to 45 minutes at a time. Small, sand-grain sized meteoroids are entering the atmosphere constantly, essentially every few seconds in any given region of the atmosphere, and thus ionization trails can be found in the upper atmosphere more or less continuously. When radio waves are bounced off these trails, it is called meteor burst communications. Meteor radars can measure atmospheric density and winds by measuring the decay rate and Doppler shift of a meteor trail.
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Meteor scattering relies on reflecting radio waves off the intensely ionized columns of air generated by meteors. While this mode is very short duration, often only from a fraction of second to couple of seconds per event, digital Meteor burst communications allows remote stations to communicate to a station that may be hundreds of miles up to over away, without the expense required for a satellite link. This mode is most generally useful on VHF frequencies between 30 and 250 MHz.
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One of the first major deployments was "COMET" (COmmunication by MEteor Trails), used for long-range communications with NATO's Supreme Headquarters Allied Powers Europe headquarters. COMET became operational in 1965, with stations located in the Netherlands, France, Italy, West Germany, the United Kingdom, and Norway. COMET maintained an average throughput between 115 and 310 bits per second, depending on the time of year. Meteor burst communications faded from interest with the increasing use of satellite communications systems starting in the late 1960s.
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"ITU - The Meteor Burst Communication Network System " The distance over which communications can be established is determined by the altitude at which the ionization is created, the location over the surface of the Earth where the meteor is falling, the angle of entry into the atmosphere, and the relative locations of the stations attempting to establish communications. Because these ionization trails only exist for fractions of a second to as long as a few seconds in duration, they create only brief windows of opportunity for communications.
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The United States Department of Agriculture (USDA) uses meteor scatter extensively in its SNOTEL system. Over 800 snow water content gauging stations in the Western United States are equipped with radio transmitters that rely upon meteor scatter communications to send measurements to a data center. The snow depth data collected by this system can be viewed on the Internet.SNOTEL Data Collection Network Fact Sheet In Alaska, a similar system is used in the Alaskan Meteor Burst Communications System (AMBCS), collecting data for the National Weather Service from automated weather stations, as well as occasional data from other US government agencies.
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Although on-site data collection using electronic measuring equipment is common-place, many monitoring programmes also use remote surveillance and remote access to data in real time. This requires the on-site monitoring equipment to be connected to a base station via either a telemetry network, land-line, cell phone network or other telemetry system such as Meteor burst. The advantage of remote surveillance is that many data feeds can come into a single base station for storing and analysis. It also enable trigger levels or alert levels to be set for individual monitoring sites and/or parameters so that immediate action can be initiated if a trigger level is exceeded.
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This necessitated the development of alternatives that would be independent of both landlines and land-based radio systems, and also satellites, all of which were thought to be possibly subject to destruction or impairment in an all-out war. The alternatives needed to be capable of being relocated, perhaps frequently, and set up rapidly in a new location when necessary. Since the facts of nuclear warfare also seemed to indicate that High Frequency (HF) Radio propagation might be disturbed by unfamiliar nuclear effects, this led to the consideration of exotic technologies such as troposcatter and meteor burst communication links. Such systems, while effective, used relatively small antennas and could indeed be transported efficiently and economically in relocatable vans.
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In the late 1970s it became clear that the satellites were not as universally useful as originally thought, notably at high latitudes or where signal security was an issue. For these reasons, the U.S. Air Force installed the Alaska Air Command MBC system in the 1970s, although it is not publicly known whether this system is still operational. A more recent study is the Advanced Meteor Burst Communications System (AMBCS), a testbed set up by SAIC under DARPA funding. Using phase- steerable antennas directed at the proper area of the sky for any given time of day, the direction where the Earth is moving "forward", AMBCS was able to greatly improve the data rates, averaging 4 kilobits per second (kbit/s).
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An automated sampling station and data logger (to record temperature, specific conductance, and dissolved oxygen levels) There is a wide range of specialized sampling equipment available that can be programmed to take samples at fixed or variable time intervals or in response to an external trigger. For example, a sampler can be programmed to start taking samples of a river at 8-minute intervals when the rainfall intensity rises above 1 mm / hour. The trigger in this case may be a remote rain gauge communicating with the sampler by using cell phone or meteor burst technology. Samplers can also take individual discrete samples at each sampling occasion or bulk up samples into composite so that in the course of one day, such a sampler might produce 12 composite samples each composed of 6 sub-samples taken at 20-minute intervals.
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