The primary LOFAR data products we use are single station dynamic spectra of a bright radio source, mainly Cassiopeia A and Cygnus A. Ionospheric disturbances will cause scintillation which shows as amplitude variations in the power spectra. We collected many years of ad hoc observations of these scintillations with many stations, both Dutch and international. Cross correlating the spectra of core stations allows for measurements on small scale moving structures, whereas with the longer baselines we can monitor larger scales.
Other LOFAR data that contain ionospheric information are the calibration solutions and all sky images.