Incoherent scatter - last update: 18 May 1999, 1400 UT


The basic principles of incoherent scatter:

The received signal is rich of physical content. From the power and the shape of the spectrum one can determine:

Several quantities can be calculated, e.g.:

Incoherent scatter is succesfully used by several radars, including EISCAT , to study Earth 's ionosphere.

Effects of strong electric fields

Under the influence of a strong electric field the directed component of the ion velocity may become comparable to the thermal speed yielding anisotropic and non-Maxwellian velocity distribution. This, in turn, may affect the analysis of incoherent scatter radar measurements! A correction to Ti is suggested by St.-Maurice and Schunk (1979) to allow anisotropic ion temperature during frictional heating. According to the theory, Ti should be replaced by (2Ti,perp + Ti,par)/3 (Williams and Jain,1986; Glatthor and Hernandez, 1990; Winser et al., 1990). Note that observations at aspect angle of 54.7 are not subject to this error (e.g., Lockwood and Winser, 1988). In addition, for magnetic field aligned incoherent scatter radar measurements which measure only Ti,par, the assumption of Maxwellian distribution is accurate to within 5% for field-perpendicular ion velocities up to 4 km/s (e.g., McCrae et al., 1991). Another important experimental effect is the change in ion composition due to increasing Ti: predominantly O+ plasma may change within 2-3 min to predominantly molecular ion plasma (Winser et al., 1990). Also this affects the analysis of the radar measurements: when there is a mixture of O+ and NO+, the standard analysis - assuming 100% O+ - can underestimate the ion temperature significantly (e.g., Glatthor and Hernandez, 1990).


See also: