Examples of RFI that only occupy a few time–frequency pixels. (a) An event that appears at 1298.562058 MHz, which is not in the frequency ranges categorized as RFI. (b) An event that appears at 1085.321323 MHz, which falls at a frequency used by civil aviation. (c), (d) Events that have similar patterns to the events in (a) and (b), but also appear in off-source observations.