Daily Image
29-01-2021
In Memoriam: Prof Ir Cees van Schooneveld (1933-2021)
| Submitter: | Jan Noordam |
| Description: | In 1978, IAU Colloquium 49 (Image Formation from Cohaerence Functions in Astronomy) was held in Groningen, to celebrate and emphasize the huge success of the new Westerbork Synthesis Radio Telescope (WSRT). It was attended by a veritable Who's Who of radio astronomy, as the world was frantically building radio telescopes. The proceedings were edited by Cees van Schooneveld, who was employed by the Leiden Sterrewacht, among other things to help atronomers to master the the "dark art" of Aperture Synthesis Calibration and Imaging. It is instructive to read his introduction (and all the contributions, really) with the benefit of hindsight. At the time, CLEAN deconvolution already existed, but Selfcal was still several years in the future. Both these transformative techniques were arrived at by intuition, and are not rigorously understood even to this day. And the proper Measurement Equation of a generic radio telescope only emerged in 1995. But since we were lucky with a near-empty radio sky, dominated by well-separated compact sources, the lack of rigor never slowed the spectacular improvement in image quality(*) in the subsequent decades. Nevertheless, now that the rich pickings of low-hanging fruit are finally exhausted, mathematical rigor has become increasingly important to fully exploit the vastly increased sensitivity, and the obscene data-volumes, of the next generation of giant new radio telescopes like LOFAR and SKA. In the meantime, Cees greatly contributed to Dutch leadership by teaching observational techniques to a generation of radio astronomers, and by promoting a professional approach to the rapidly developing field of Signal Processing. He was PhD supervisor to Albert Bos, who was responsible for the other half of the sustained success of the WSRT, by virtue of his superior digital correllators. Their complete absence of "closure errors" was part of the enlightened "over-engineering" of the WSRT, which was crucial for making these wonderful images possible. (*) By 4-5 orders of magnitude, wide-field and wide-band, and in full polarisation. |
| Copyright: | Rudolf le Poole |
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