Speaker: Dr. Philip J. Erickson of the MIT Haystack Observatory (http://www.haystack.mit.edu/)
Date: Wednesday, November 13, 2013 @ 7:00 PM
Location: Squires 219
The coupled near-Earth space system is a complex and dynamic region where both large and small scale physics governs our planet's reaction to space weather disturbances from our nearest star, the Sun. Much of this fascinating environment is invisible to optical techniques, but is revealed at radio frequencies in the centimeter wavelength range. Observing in radio usefully allows study of the terrestrial geospace system from the ground.
For more than 5 decades, it has been practical to scatter UHF radio waves off the free electron gas in the upper atmosphere, modified by the presence of charged ions, in a process known as Thomson or incoherent scatter. This most powerful of ground based techniques allows the natural plasma made each day by our sun's extreme ultraviolet radiation to be probed at appropriate space and time scales. However, the radar target provided by the ionospheric plasma is an extremely weak and variable one, requiring megawatt class transmitters, sensitive receivers, and large aperture antennas. Maintaining these subsystems and interfacing legacy transmitters to modern receiver hardware is a constant and unique challenge.
I will describe the general design and operation of radars capable of detecting incoherent scatter along with the use of these radars to derive the complete physical state of the thermal ionospheric plasma. Along the way, I will describe the basics of how plasma scatter occurs at tens of centimeter wavelengths. I'll also provide specific examples of radio and radar techniques used on a routine basis at the mid-latitude Millstone Hill ionospheric radar system, operated at MIT Haystack Observatory since 1960 as an upper atmospheric facility for the space science community. Some of these techniques will be familiar to the 70 cm radio amateur community. Finally, I will briefly describe some significant scientific results arising from these uniquely productive observations.