LOFAR S₄ of Cassiopeia A (a, b) and Cygnus A (c, d) calculated for days 87 (quiet) and 90 (disturbed) in 2017, recorded on LOFAR station PL612. GNSS ROT values were calculated for 1 s (e, f) and 60 s (g, h) for days 87 and 90 of 2017. GNSS S₄ index (i, j) observed on L1 (blue dots), L2 (red dots) and L5 black dots) frequencies recorded with the ionospheric monitor co-located with the PL612; LOFAR scintillation indices for the 48.92 MHz channel (from Figs. 4a to 4d) are also shown as pink area (Cas A) and blue area (Cyg A). Gaps in the GNSS scintillation indices were due to issues related to data downloading.