Decoding of Barker-coded incoherent scatter measurements by means of mathematical inversion

Abstract. The standard analysis of Barker-coded incoherent scatter experiments is based on a matched filter with an im-pulse 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 correspond-ing effect is also encountered in the lag direction, where indi-vidual 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 in-version problem. Error analysis also indicates that the statis-tical 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 vari-ation 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 pro-cessing; instruments and techniques