## 5 Conclusions  
In our work we present observational data of two pulsars, PSR J0332+5434 and PSR J1509+5531, obtained using the LOFAR station located in Baldy, designated PL612. This data was confronted with the data obtained by the IGS LAMA receiver located in Lamkowko. Both of these instruments are owned and managed by UWM. In our investigations firstly we searched for all the instances when the satellites of the navigators were closer than 3 angular degrees from the pulsar. Results of this search are presented in Figure 6.  
Our main objective was to assess if the LOFAR pulsar observation characteristics performance in face of the ionospheric plasma gradients can be compared with the GNSS TEC fluctuations. Pulsar data has been prepared and measured for all retrieved close-ups. We used 1-min integrated profiles to determine the maximum relative flux by using of Gaussian fit to main profile component. The one-minute integration time is connected with the physical processes causing the flux variation (Figure 2). For all the moments of relative flux determination we also measured ROT value. Figure 8 shows the corresponding graphs integrated for all the satellites close-ups in the period in which pulsar was observed. Figure 10 also confirms that increasing trend of the ROT values corresponds with the negative trend in the pulsar peak intensity and vice versa. As a result of our study, we can confirm, that there exists an echo of ionospheric fluctuations (observed with ROT) in a pulsar's flux intensity registered with LOFAR PL612 station. It is proven by a strong negative correlation between the ROT value and pulsar's peak flux, the most evident, when looking at jumping values (strong increase of a ROT value corresponds directly with a decrease of the pulsar's peak flux and vice versa). The important result of our work was the start work on the creation of a multi-instrumental tool based on LOFAR and GNSS that, independently, associated with observations of extraterrestrial sources of long radio waves, will allow the assessment of the state of the ionosphere. The results obtained in our research can be especially useful for those pulsar observations in LOFAR program which require good control of ionospheric conditions. A system could be created that would search these close-ups. As we showed before, even for longer pulsar observations there will be only a few such close-ups, but even this may allow ionospheric changes to be assessed by the interpolation method. This will allow, at least roughly, to remove the influence of the ionosphere from the observation. The corrections to the pulsar flux measured on this basis could then be applied to the data, significantly improving their quality and, above all, reducing the chance that the ionospheric effects would be taken for some new effect in the pulsar radiation mechanism. In future works we plan to increase the number of used LOFAR stations, which would allow us to perform more detailed observation of particular ionospheric structures and involving additional instruments such as ionosondes. Conceptualization, L.P.B. ; methodology, L.P.B. and A.K. ; software, P.F. ; validation, L.P.B., P.F., K.K. and A.F. ; formal analysis, A.K. and W.L. ; investigation, L.P.B. ; resources, L.P.B. and A.K. ; data curation, P.F., K.K. and L.P.B. ; writing--original draft preparation, L.P.B. ; writing--review and editing, A.K., K.K., A.F. and W.L. ; visualization, L.P.B. and P.F. ; supervision, A.K. and J.K.; project administration, A.K. ; funding acquisition, A.K. and W.L. All authors have read and agreed to the published version of the manuscript. **Funding:** The UWM and UZ contributions are supported by the Ministry of Science and Higher Education (MSHE), Poland, for granting funds for the Polish contribution to the International LOFAR Telescope (MSHE decision number DIR/WK/2016/2017/05\(-\)1) and for maintenance of the LOFAR PL-612 Baldy (MSHE decision number 59/E-383/SPUB/SP/2019.1).