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 Earth's 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.
The Observatorio del Ebro has made significant contributions to the
exploration of Earth's ionosphere using radio sounding, and today is part of
a network of digisondes that provides real time electron density profiles
from some 60 locations around the globe via the Internet. The modern
sounding techniques that were developed in the last decade for ground-based
observations have 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 NASA's 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 water on the moons.

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International Workshop "Challenges of Geomagnetism, Aeronomy, and Seismology 
in the XXI Century" on the occasion of the Centennial of Ebro Observatory, 
Tortosa, Spain, 29 September - 1 October 2004.