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Ann. Geophys., 26, 571-581, 2008
www.ann-geophys.net/26/571/2008/
© European Geosciences Union 2008
Lag profile inversion method for EISCAT data analysis
I. I. Virtanen1, M. S. Lehtinen2, T. Nygrén1, M. Orispää2, and J. Vierinen2
1Department of Physical Sciences, University of Oulu, P.O. Box 3000, 90014, Finland
2Sodankylä Geophysical Observatory, 99600, Sodankylä, Finland
Abstract. The present standard EISCAT incoherent scatter experiments are based on
alternating codes that are decoded in power domain by simple summation and
subtraction operations. The signal is first digitised and then different
lagged products are calculated and decoded in real time. Only the decoded
lagged products are saved for further analysis so that both the original data
samples and the undecoded lagged products are lost. A fit of plasma
parameters can be later performed using the recorded lagged products. In this
paper we describe a different analysis method, which makes use of statistical
inversion in removing range ambiguities from the lag profiles. An analysis
program carrying out both the lag profile inversion and the fit of the plasma
parameters has been constructed. Because recording the received signal itself
instead of the lagged products allows very flexible data analysis, the
program is constructed to use raw data, i.e. IQ-sampled signal recorded from
an IF stage of the radar. The program is now capable of analysing standard
alternating-coded EISCAT experiments as well as experiments with any other
kind of radar modulation if raw data is available. The program calculates the
ambiguous lag profiles and is capable of inverting them as such but, for
analysis in real time, time integration is needed before inversion. We
demonstrate the method using alternating code experiments in the EISCAT UHF
radar and specific hardware connected to the second IF stage of the receiver.
This method produces a data stream of complex samples, which are stored for
later processing. The raw data is analysed with lag profile inversion and the
results are compared to those given by the standard method.
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