On Tuesday, September 23, Juha Vierinen, a post-doc at MIT came to campus to give a talk on his work at the Haystack Observatory. Vierinen works to take statistical measurements of our atmosphere.
When most people think of the atmosphere, they don’t often think of plasma, but it is definitely there. When the energetic ultraviolet light from the sun hits the Earth’s atmosphere, part of its outermost region ionizes, creating a soup of positively and negatively charged particles. If the density of the ionized gas is low enough, it becomes plasma. This plasma region starts about 90 km above the planet’s surface.
The effects of atmospheric plasma can be visible to the naked eye under the right conditions.
One of the things he can measure is the electron density in a certain region of the atmosphere. The electrons in plasma can move freely, and since they are so light, it doesn’t take much to get them going. Once one electron starts move, it effects all of its neighbors. Eventually, this results in positively and negatively charged regions, which can be detected based on the way they reflect electro-magnetic waves.
Vierinen uses Software Defined Radios (SDRs) to detect signals. These are systems where using software components, instead of traditional hardware components. This technology is actually quite accessible to the average person. Though some of the systems can cost thousands of dollars, others are quite affordable. Vierinen mentioned a small USB-powered device costing only eight dollars capable of detecting an airplane within several hundred kilometers! These utilize passive radar: they don’t transmit their own signals, but they rely on the reflected waves from other sources and are thus much cheaper. Vierinen connects many of these devices into a powerful array for a very low price. Additionally, much of the software used is open source (based on the GNURadio platform) but it is still quite powerful.
Vierinen’s work applies to more than the study of plasma physics. For example, he has developed an open source receiving software that is used by the military for missile detection.
Vierinen’s developments have thus significantly lowered the price of an otherwise expensive process. They have both scientific and practical applications, from plasma physics to missile detection, and they certainly have yet to reach their full potential.