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The Birds

Submitter: Gyula I.G. Jozsa
Description: There are several stories about how wildlife influences the daily business of astronomers. This one is about crows.

Some time after the current receivers of the Westerbork Radio Synthesis Telescope were installed, it turned out that the polystyrene covers (radomes), a measure to protect the receivers against rain and moisture, were discovered to also be very handy as a source of nesting material by a bunch of "kauwen" living in the local neighbourhood. We disagreed, and since barbed wire is not a very good idea for protecting a radio receiver, hard plastic covers were glued to the sides of the radomes, such that our feathered friends could not find any hold on the radomes any more.

Birdless measurements were taken over the years, unaware of the fact that shortly after, the system temperature of the receivers, a measure for the noise that enters the system, started to increase. The system temperature has large variations from day to day. Only by heavily smoothing and filtering the measured system temperatures, as shown in the image above, it becomes evident that the average system temperature increased over the years. Only after a few years, astronomers from ASTRON noticed this. Our subsequent investigations revealed that moisture was stored between the polystyrene and the hard plastic covers, and that this was causing a significant increase in system temperature (with yearly periodic variations).

Recently, new radomes, without anti-bird-protection, have been placed on the receivers, and now we have gathered enough statistics to show that in the most frequently used L-band the system temperature has decreased on average by ~12%, which is equivalent to a decrease of ~25% in observing time to reach the same level of sensitivity.
Copyright: Copyright by ASTRON
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