Ionospheric scintillation indexes for LOFAR single station observation mode

<pre>LOFAR single station observation mode is often used for ionospheric studies. Observations of A-Team (the brightest radio sources CasA, CygA, TauA) enables measure of ionospheric scintillation. Relatively low brightness of the radio sources compared to signals coming from the Earth and originating from man-made activity (in particular RFI) can make the analysis difficult. In order to fully utilize the data, it is necessary to apply methods that eliminate interference. Combination of broadband observations and careful selection of observation frequencies should also improve the results. Another problem is the frequency (very low compared to GPS) which requires very careful data analysis. We observe large structures in relatively quiet conditions and low velocity of ionospheric drift resulting in low frequency scintillations compared to GPS. Amplitude observations conducted as a standard observations suggest using the S4 index to monitor the state of the ionosphere. In this paper, we present methods for calculating the S4 index for LOFAR data that eliminates the obstacles mentioned above. We compare different methods that resolve the problem and present the results. Signal spectra were also examined in detail to explore the possibility of using them to eliminate interference effects. The analyzes were carried out on the basis of data collected during the last 3 years at the PL610 station in Borowiec.</pre>