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Johan Hamaker turns 75

Submitter: Jan Noordam
Description: In our AJDI series of ex-employees who are still active for ASTRON (or JIVE) at 70, we now celebrate Johan Hamaker, who has turned 75 last week. For a few days each week he may be found in the "dinosaur room" in the prestigious Pavillion West, together with other giants like Wim Brouw and Hans van Someren Greve.

Johan started his career with impeccable credentials, since his JornaRoos (also in the picture) is a niece of Prof Oort, the father of Dutch radio astronomy. He is also a bit of an oddity, since he is the only ASTRON ingenieur who did not receive his education at a Technical University, but at the University of Amsterdam. Not surprisingly, he speaks 7 languages and knows his classics.

Johan was part of the original group that cheerfully over-engineered the WSRT, just to be on the safe side, and thus paved the way for its sustained excellence. At the same time, together with Jaap Baars, he introduced a less formal atmosphere at the Dwingeloo establishment, where people still addressed each other by surnames, wore jackets and ties, and the boss was always right. He was involved in various hardware projects, some of which were quite revolutionary, but his real interest was in the use of software for calibration. He rose to acting head of the "Computer Group" in the early eighties, and was seconded to Hawaii for a few years to help with the JCMT.

During the seventies, for good practical reasons, the WSRT data were processed in Leiden. Unfortunately, this meant that there was very little software in Dwingeloo (or even Westerbork) to inspect the data and develop new calibration techniques. Johan played a large role in redressing this unhealthy situation by developing software tools for imaging and display. This started the process that has kept ASTRON in the forefront of ultra-quality calibration to the present day.

His finest hour came around 1995, when he formulated the Measurement Equation, a closed-form matrix formalism that describes a generic radio telescope in full polarisation. Of course this was the culmination of a decades-long search by many people around the world, but he had the idea that made it all fall into place. It was just in time too, since it would have been unthinkable to embark on the new generation of giant radio telescopes (LOFAR, SKA, etc) without the Hamaker-Bregman-Sault (HBS) formalism.

Because he can afford to, Johan has been generous in admitting that he might (perhaps) have been too severe in his early prediction that LOFAR could never be calibrated. His unusual career is yet another demonstration that "it takes all kinds to make the difference".

Copyright: JPH
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