[6] The ionosphere investigation by the Kharkov IS radar is based on the measurements of the signal correlation function (CF). Measurement and data processing methods were described by Taran [1979, 2001], Emel'yanov [1999], Lysenko [1999a, 1999b], and Pulyaev [1999]. From the measured CFs, electron Te and ion Ti temperatures, ion composition, vertical component Vz of the plasma drift velocity and other ionospheric parameters are derived. The electron density profiles Ne(h) are obtained using the power profile method from the following formula [Evans, 1969]:
![]() | (1) |
[7] The errors in estimation of the signal CFs and ionospheric parameters depend on the signal-to-noise ratio, noise background, parameters of the equipment, and other factors. Table 1 shows the statistical errors of ionospheric parameters for typical daytime conditions, 15-min signal integration, and the given signal-to-noise ratios.
[8] The vertical plasma velocity
Vz is found from the Doppler
shift of the IS signal spectrum estimated based on the measured
quadrature components of the signal CF
[Emel'yanov, 1999].
To
increase the accuracy of the measurements, a trapezoidal
smoothing of CF over altitude is performed
[Holt et al., 1992;
Lysenko, 1999a].
The RMS deviation
sVz of the measured velocity
depends on the signal-to-noise ratio
q and varies with altitude.
Usually,
sVz 5-20 m s-1
for altitudes of the ionospheric
F region
at
q
0.2 and an integration time of 15 min.
[9] The method used to determine
Ti and
Te temperatures
should be considered in more detail. These temperatures are
calculated taking into account the ion composition at altitudes
below the
F2 layer peak. In this case the
Te/Ti and
Ti/mi ratios,
where
mi is ion mass, are found from the measured CFs of a
scattered signal
[Farley, 1969]
by comparing these functions with
the theoretical CFs using the least squares technique. Certain
conditions are imposed in order to eliminate the ambiguity in the
solution of the problem
[Pavlov et al., 1999;
Schlesier and Buonsanto, 1999].
The average molecular weight of ions
(O2+ and
NO+ ) was taken equal to 31. Gradual transition from the 100%
concentration of molecular ions at 120 km altitude (where it was
considered that
Te Ti
Tn
355 K) to the 100% concentration of
O+ ions at an altitude of 230-300 km
was assumed. This height was
selected depending on specific conditions: day-night, winter-summer.
A change in
Ti within an altitude interval of 10 km is
restricted additionally:
DTi( max) =
0.1 Ti. It should be noted that
the applied technique only approximately reflects changes in the
concentration of molecular ions, which are especially significant
during magnetic disturbances, and results in additional error in
determining
Ti,
Te, and
Ne. The problem of correcting measured
ionospheric parameters
Ti,
Te, and
Ne depending on the applied
model of ion composition was first discussed by
Waldteufel [1971].
It is known that this problem is solved in the modern models of the
ionosphere [see, e.g.,
Mikhailov and Schlegel, 1997;
Schlesier and Buonsanto, 1999].
A comparison of the data on electron density
obtained by the Kharkov radar using the power profile
technique and the Faraday rotation measurements (this technique is
described, e.g., by
Grigorenko [1979])
made it possible to estimate
the error in determining
Ti and
Te below
F2 region peak. This error
was not higher than 15% under quiet conditions.
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