Putting Meteors to Work
It has been estimated that during a typical 24-hour period, the earth encounters as many as 200 million meteors ("shooting stars") that are bright enough to be seen with the naked eye if they fell at night. At any given location on a clear, dark night, about 50 per hour is a typical sighting rate. Although meteor sightings vary from place to place, any two observers separated by not more than about 300 miles can usually see the same meteor if its trajectory falls somewhere between them (this distance extends out to about 1000 miles if instrumental sightings are counted).
So what? Well, consider replacing the observers with two radio antennas. As a meteor enters the atmosphere, it leaves behind a trail of ionized particles (primarily electrons) that acts as a good radar target at altitudes of between 50 and 75 miles. The trail is also a good reflector of radio waves--radar itself is nothing more than a focused beam of ultra high-frequency radio waves. With such a reflector, the hypothetical antennas can now "talk" to each other. In Alaska, these antennas are no longer hypothetical, and two networks utilizing the principle (one a federal consortium and one private) are now in operation at widely scattered localities around the state.
The ionization of most meteor trails persists for only 300 to 500 milliseconds (0.3 to 0.5 seconds), but with modern communications technology, a lot of information can be transmitted in less than a second. Ken Kokjer and Tom Roberts of the Institute of Northern Engineering at the University of Alaska in Fairbanks report that 250 milliseconds--a quarter of a second--of transmission is long enough to transmit the information needed for most scientific applications. And, while high frequency (HF) communications at high latitudes are unpredictable and often "blacked out" by the aurora, communications by meteor scattering are not perceptibly affected.
Much of the data being transmitted by "meteor scattering" is environmental information from remote unmanned sites on such matters as snow depth, rainfall, stream flow, wind velocity, temperature, humidity, etc. Weather data are routinely gathered like this by the National Oceanic and Atmospheric Administration's Weather Service, for example. Many other scientific projects also reap the benefits.
The data-gathering facilities of the Alaska networks consist of two master receiving sites (both in Anchorage) which collect the signals from many remote, unmanned transmitting facilities around the state. Typically, a master facility cues each of the stations in its network to "dump" its data on an hourly basis. It keeps prompting until an appropriate meteor trail appears. When this happens and a field station receives the message, it responds by transmitting the information back to the master station. The master station then acknowledges receipt and a new data collection cycle begins. All this takes place in the one-quarter second mentioned earlier.
Longer messages can be sent when the information is plain text and not formatted scientific data. This is accomplished by sending the text in sequential quarter-second bursts. In other words, meteor scattering can be used for regular communications also.
To take one example, the University's Institute of Arctic Biology is operating a research field camp on Toolik Lake near the pipeline on the northern flanks of the Brooks Range. Meteor scattering is the preferred method of communication between this camp and Fairbanks on matters of logistical support. Kokjer estimates that a short message ("send another case of beans on the next plane") averages about a five-minute delay before an appropriate meteor trail appears. Very long messages can be spread out among successive meteor trails. With a little patience and a few shooting stars, the word gets through.
