When a meteor enters the atmosphere at high velocity it burns up leaving trails, sometimes even visible during daylight, though the majority of meteor trails can only be seen at night. However another method of meteor detection exists which does not need dark skies, and also is far more sensitive, detecting micro meteors not visible even during the night. This method involves the use of radios and antennas. How does this work?
As meteors burn up in the atmosphere between 80 km and 110 km altitude they ionize (stripping electrons off atoms) the air. This ionized air under the right conditions functions as a "mirror" for radio frequency waves (such as shortwave transmissions, TV stations, FM radio, radars.) The mirror exists only for a brief period, but long enough to detect reflected radio waves.
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| Meteor Echo Spatial Relationship between Meteor, Transmitter, and Receiver |
For these mirrors to be useful the sources of radio signals need to be below the horizon and thus beyond normal reception. Otherwise you would receive those signals anyway, meteors or not. However since the altitude range of meteor burnup is relatively narrow the transmitter and receiver can not be too far either, because reception will not be possible even if a meteor is range of either transmitter (but not the receiver) or receiver (but not the transmitter.) Separation between transmitter and receiver must be just right, both must share a common volume of the sky. Only when a meteor leaves a temporary "mirror" in the common volume should these signals be receivable. If these conditions are met, then using proper hardware and software, these mirrored signals can be demodulated, and made audible and visible.
I have multiple setups (see photos section) operating around the clock and normally live stream at least one of them to YouTube. The primary software used is SDR Radio, though I regularly experiment with other software. The RF signal I monitor is off an analog TV station transmitting on 55.24 MHz (channel 2) in Sault Ste. Maries, Ontario, Canada. The receiving antenna is custom build 3 element Yagi located in Minneapolis, Minnesota, US, pointing ENE. Best echoes occur late evening through late morning, US time.
A meteor echo will make a sound above the background noise and generate a colored spot or streak ranging from yellow to red. Occasionally very strong meteor echoes will occur which generate long streaks and sounds, often accompanied by multiple side streaks which are the result of FFT windowing artifacts. A diagonal line at the start of a meteor signal is a head echo, often sounding like a whistle with a decreasing pitch.