A morphological algorithm for improving radio-frequency interference detection

¹ University of Groningen, Kapteyn Astronomical Institute, PO Box 800, 9700 AV Groningen, The Netherlands
e-mail: offringa@astro.rug.nl
² University of Groningen, Johann Bernoulli Institute for Mathematics and Computer Science, PO Box 407, 9700 AK Groningen, The Netherlands
e-mail: j.j.van.de.gronde@rug.nl; j.b.t.m.roerdink@rug.nl

Received: 22 November 2011
Accepted: 11 January 2012

Abstract

A technique is described that is used to improve the detection of radio-frequency interference in astronomical radio observatories. It is applied on a two-dimensional interference mask after regular detection in the time-frequency domain with existing techniques. The scale-invariant rank (SIR) operator is defined, which is a one-dimensional mathematical morphology technique that can be used to find adjacent intervals in the time or frequency domain that are likely to be affected by RFI. The technique might also be applicable in other areas in which morphological scale-invariant behaviour is desired, such as source detection. A new algorithm is described, that is shown to perform quite well, has linear time complexity and is fast enough to be applied in modern high resolution observatories. It is used in the default pipeline of the LOFAR observatory.