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Ann. Geophys., 22, 3-13, 2004
www.ann-geophys.net/22/3/2004/
© European Geosciences Union 2004
Decoding of Barker-coded incoherent scatter measurements by means ofmathematical inversion
B. Damtie1, M. S. Lehtinen2, and T. Nygrén1
1Department of Physical Sciences, University of Oulu, P.O. Box 3000, FIN-90014, University of Oulu, Finland
2Sodankylä Geophysical Observatory, FIN-99600, Sodankylä, Finland
Abstract. The standard analysis of Barker-coded incoherent scatter experiments is
based on a matched filter with an impulse response which is a mirror image
of the code itself. The method produces small sidelobes which cause
contamination from regions outside the nominal range gate. A corresponding
effect is also encountered in the lag direction, where individual lag
estimates are biased by the variation of the plasma autocorrelation
function around the nominal lag value. The present paper introduces a new method of
analysing Barker-coded experiments by means of stochastic inversion. Since it does
not apply a decoding filter, it does not suffer from drawbacks caused by the
sidelobes of the range ambiguity function. The method combines the profile of
each full lag and a number of surrounding fractional lags into a single inversion
problem. Error analysis also indicates that the statistical accuracy given by
inversion is better than that obtained by means of standard decoding. Furthermore,
the inversion method gives a possibility to reduce the bias due to the
variation of the autocorrelation around the nominal lag. In this paper the method
is described and applied to data obtained by means of the EISCAT Svalbard radar.
In addition, it is shown that mathematical inversion can be used instead of the the
conventional height integration.
Key words. Radio science (ionospheric physics; signal processing; instruments and
techniques)
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