Example of the SIR operator applied on a LOFAR observation, displaying five different methods to make the SIR operator two-dimensional. The visibilities shown are from baseline CS003  ×  CS007 of a LOFAR low-band-antenna (LBA) observation with 3s  ×  0.8 kHz resolution. This observation part was selected as an example because it has a two-dimensional RFI structure. Such RFI is less common, hence this is not a typical case. With the exception of the intersection, there is no difference between the different methods on the thin lines below 32.1 MHz. Applying the operator sequentially (panels d)–f)) is more aggressive for the two-dimensional structures, as it will flag samples that have diagonal neighbours that are flagged. Intersecting the two methods (panel b)) will only flag concave samples. Pink is pre-flagged by the SumThreshold method, yellow is added by the SIR operator. A value of η = 0.2 was used in this example.