Remote Sensing of Geospace Plasmas with Radio Waves

Bodo W. Reinisch
Environmental, Earth, and Atmospheric Sciences Department
Center for Atmospheric Research
University of Massachusetts Lowell, USA


One hundred years ago, Guglielmo Marconi took advantage of the reflecting
properties of EarthÕs ionosphere to transmit radio signals from England to
America. In the decades that followed, techniques were developed to use
radio waves for the remote exploration of the ionosphere.  The remote
sensing makes use of different physical mechanisms in geospace plasmas:
specular reflection, coherent scatter from magnetic field-aligned plasma
irregularities, incoherent scatter from thermal plasma waves, and refraction
and dispersion of trans-ionospheric signals. This talk will concentrate on
the specular reflection technique, usually referred to as Òradio soundingÓ.
Modern sounding techniques were developed in the last decade for
ground-based observations that led to a network of digisondes that provides
real time electron density profiles from some 60 locations around the globe
via the Internet. This technology has also been exported to space for the
exploration of magnetospheres and ionospheres of the Earth and other
planets. Latest results of the radio plasma imager (RPI) on NASAÕs IMAGE
satellite will illustrate how low-power very-low-frequency radio sounding
can measure magnetospheric plasma density distributions over distances of
several earth radii. New versatile digital sounding systems are under
development for the exploration of the magnetoplasma environment of Jupiter
and its moons, as well as probing for subsurface water on the moons.

_______________
Seminar given at Air Force Research Laboratory, Hanscom Air Force Base, 
October 20, 2004