Two regular readers wrote asking for more details on using radio scatter to "listen" to meteor tracks - something I do when it is too cloudy or light polluted to watch a meteor shower.
Radio waves travel in straight lines - the reason why we sometimes have communications that are not line of sight is mostly due to reflection. This is really important for long range radio communication. It turns out there are ionization layers from about fifty to a few hundred miles above the Earth. There is a very small amount of atmosphere at those altitudes and UV and higher energy radiation from the Sun is enough to knock off an electron or two from these molecules. The negative electrons want to reattach to a positively changed atom, but the distance between the two is now so great that it can take quite awhile. The net result, when there is a lot of energy being dumped into the layer - is that a plasma forms. This makes a nifty mirror.
A lot of physics is involved and depending on the nature of the gases available, their density and how they are energized, the reflection and absorption properties of these layers strongly depends on the wavelength of a radio signal that is pointed at them. Longer wavelengths - AM and shortwave radio - tend to have strong and useful effects. You probably have noticed that you can listen to an AM radio station well over the horizon - even thousands of miles away - when the Sun goes down. Shortwave radio DX - the practice of "working" distant sites - uses this in what can be a very sophisticated way.
In the 20s when Bell Labs was doing very careful radio propagation measurements, it was noticed bursts of distant signals sometimes appeared during meteor showers. It turns out that a meteor dumps a lot of energy into the atmosphere that slows it down. The closing speed of the average Perseid meteor is about 37 miles per second and they last about a second - so almost all of their energy is dissipated in a very small cylinder of atmosphere about 40 miles long and 80 to 100 miles up.
Electrons from this gas are stripped and it takes seconds for them to recombine. For certain radio frequencies this makes a nifty reflector. If the reflector is between me and a radio station (30 to 50 MHz is nearly ideal it turns out, but FM radio -- about 100 MHz - isn't bad either) that is over the horizon it is possible for me to me to receive it for a few seconds.
The government (military and scientific projects) and even a company or two use the statistical likelihood of small meteors being around to reflect communications to operate low data rate networks. This is a really cheap way to get a signal over the horizon and not use a satellite or ground based network. Generally you keep sending a short amount of information over and over - eventually it is heard and recorded at a base station which sends an acknowledgement - when you receive that you can start all over again. (there are more energy efficient burst detection protocols, but the idea is similar)
I've been fascinated with very low data rate communications for a long time and this makes sense for some people. One project that has been rolling along for about 40 years is SNOTEL, which gives daily (and better) snow and precipitation information for the Western US and Alaska. It would have been far too expensive to rely on satellites or conventional ground based networks. Really nifty!