Meter radar measures radio reflections off particles the size of a grain of sand at 100 kilometer distance. Let’s find out more.
Watching my HF spectrum recently, I came across an interesting signal on 17.45 MHz, shown above. After some digging, I discovered the source as the Canadian Meteor Orbit Radar, or CMOR. It’s run by the Department of Physics and Astronomy at University of Western Ontario.
Now what I was seeing was the actual radar transmitter at London, Ontario about 3,000 km east of Calgary. It sends over 500 75 μs pulses per second and watches for meteor reflections. All in all, CMOR tracks 2,500 meteor orbits a day using three radar stations on 17.45, 29.85 and 38.15 MHz.
Hams refer to bouncing signals off meteor trails as “meteor scatter“. You may have head that hams use mainly digital modes to communicate using meteors in short bursts. Typically, this mode of communications is done on 10, 6 and 2 meters, although higher frequencies are possible.
Meteors occur when meteorites, or small rocks, enter our atmosphere at fairly high speed. Friction causes these rocks to melt, and leave behind a trail of ionized particles in the atmosphere. You will find that these trails last from a few seconds to a few minutes, during which time they reflect radio signals back to earth.
Meteor Radar – How It Works
Typical meteor radar frequencies are from 30 to 100 MHz, with a sweet spot around 40-50. These meteor trails occur mostly at 70-120 kilometers altitude, and form a cylinder 10-30 kilometers long.
You will find around 30 meteor radar stations around the world, with two purposes. First, to measure meteor angle of arrival, speed and height. Second, and more important for the scientists, is to study wind, temperature, pressure and other parameters of the upper atmosphere.
From a propagation perspective, meteor trails occur just below the E-layer and provide good (although short lived) propagation over 500 to 3000 kilometer ranges.