Daily Image
25-08-2014
Attention to Detail
| Submitter: | Madroon E.J. |
| Description: | The unusual success of institutes like ASTRON or JIVE is rooted in many factors, and one of them is an unusual attention to detail. Not many people would notice that even the license plates of our small fleet of limousines proudly reflect a significant part of our core business(****). Part of our core business is to make (ultra) high-quality images of the radio sky, using arrays of radio antennas. An important problem is the instrumental Point Spread Function (PSF) pattern around all radio sources, which often takes the shape of rings or radial spikes. Since the magnitude of the PSF is proportional to the source flux, the patterns around bright sources tend to obliterate the much fainter radio sources in which we are interested. For a sparsely sampled imaging instrument like a radio aperture synthesis array, the PSF extends over the entire field(***), and has to be removed from the data with extreme accuracy(**). After all, one cannot study what one cannot see. Fortunately, we are very good at subtracting unwanted radio sources (and their PSF). Our instruments are designed with unusual care, and our data reduction software is unusually sophisticated. As a result, the unofficial world record has been held by our WSRT for many years, with a Dynamic Range(*) of well over one million. At this moment, the record is briefly held by one of our esteemed competitors (the JVLA), but only by using software that was developed at ASTRON. We expect that the Blue Riband of Dynamic Range will soon be recaptured again by LOFAR, in its search for the elusive Epoch of Reionization. This obsession with getting the most out of our imaging instruments may have seemed a bit of a luxury pursuit in the past. But it has proved to be an essential preparation for the new generation of giant radio telescopes, like LOFAR and SKA. These will require an even higher dynamic range, and a PSF with carefully controlled sidelobes, to exploit their much greater sensitivity. And since the devil is in the details, these require unusual attention. (*) The Dynamic Range (DR) of an image quantifies the ability to see faint objects in the presence of (the PSF of) very much brighter ones in the same field. (**) A bit like removing the Sun from the daytime sky, so we can see the stars. (***) For a fully sampled imaging instrument like an optical telescope, the PSF is much smaller, so it only ruins a small area around bright sources. (****) Apart from the magic letters PSF, the license plate indicates that our images get very close to the Truth (symbolized by the number 42), and that a Dynamic Range of 6 orders of magnitude is a minimum requirement for club membership. |
| Copyright: | Madroon Community Consultants (MCC) |
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