– Radio Observatory and International LOFAR Telescope
Our Radio Observatory department is responsible for the exploitation of the Westerbork Synthesis Radio Telescope (WSRT) and the Low Frequency Array (LOFAR). These instruments are quite different, from a technical point of view: the WSRT has larger and more complex mechanical/electrical elements, while LOFAR has a multitude of electronic components and a critical dependence on large-scale ICT . Besides that, they operate in a different stage of maturity: the Westerbork Telescope has been in use since 1970, and has been modernized several times, whereas LOFAR has only been fully operational for a few years now.
After many years of development, initial operations and testing by expert astronomers, at the end of 2013 the International LOFAR Telescope had become such a robust and mature instrument, that it was possible to give a wide range of researchers from around the world access to the telescope. More than 100 science teams with hundreds of researchers have made use of it in 2014 and 2015. The best of the submitted applications to use the telescope for specific science were selected, and they have gathered lots of valuable new research data. To enable the astronomers to use LOFAR optimally, our Science Support employees have organized various courses and trainings. Not only did they explain the technical possibilities to use LOFAR, they also demonstrated advanced techniques to process and analyze the received data.
The amount of data collected with LOFAR is enormous. At the end of 2015 there was already 20 Petabyte (20 PB = 20,000 TB = 20,000,000 GB) of data in the long term archive. Each year this amount increases by 6 or 7 PB. All data is processed through a powerful computer cluster in Groningen and distributed towards data centers in Amsterdam, Groningen (NL), Jülich (D) en Poznan (P). The long term archive is publicly available, also for science use by different groups in ways not foreseen by the original observers.
In 2014 and 2015 the Radio Observatory focused on enabling all of the users of LOFAR to do more with the instrument and make even better use of it. We have seen tremendous development and expansion in the range of capabilities of LOFAR and in its ease of use.
In order to control LOFAR and to combine and process all of its data, we need huge computing power, network capacity, and data storage. The computing system needs to be finely tuned to the task. In 2014 we have implemented a new central online processing system by the name of COBALT (COrrelator and Beamforming Application platform). Using standard GPU components, the system architecture and software for COBALT was entirely developed in-house. We also had to develop and build extra cooling devices. In collaboration with ASTRON’s Research & Development department, we completed, within 10 months time, an impressive new system with which LOFAR can function for the years to come. COBALT has also led to substantial operational cost savings, which are now only 10% of the yearly costs we made for the equivalent processing in previous years. I am very proud and satisfied with this strong team achievement!
New imaging software Besides the new online computing cluster, we also participated in developing new imaging software for LOFAR. Now we can generate images with much higher quality, at higher resolution, from the observed data. A special Calibration & Imaging Tiger Team realized this project in 2 years. Quite an achievement with a tremendously useful outcome!
New International LOFAR stations In 2014 and 2015 we have procured, constructed and taken into use four new LOFAR stations: one in Germany in 2014, at Norderstedt near Hamburg; three in Poland in 2015, at Łazy near Krakow, Borówiec near Poznan and Bałdy near Olzstyn. In total there are now 12 LOFAR stations outside the Netherlands in Europe; more are being planned. The Polish community, collected in the POLFAR consortium, has also formally joined the LOFAR International Telescope Foundation in 2015. Through the Polish National Supercomputing and Networking Center, they are now contributing capacity to the LOFAR archive.
WSRT Unlike LOFAR, the 14 dishes of the Westerbork Synthesis Radio Telescope are fully mature. In 2014 we began to take these dishes out of the operational array one by one, to make them ready for a new life cycle. In June 2015 we did the last observations with the existing receivers, and ended the project cycle festively. Of the 14 telescopes, 12 will soon receive new “cameras”, called APERTIF (APERture Tile In Focus). They will replace the old receivers from the 1990’s; the central processing systems will also be completely replaced. Experimentation with prototypes of these new cameras has been ongoing; they offer a much wider instantaneous field-of-view for imaging, and will be great for surveying the sky. The installation of the full APERTIF hardware is expected for 2016. In the meantime we have conducted large-scale maintenance of all the telescope dishes. We have painted all constructions and completely renewed all the cables. Modern telescope control circuitry was also developed and tested.
The remaining 2 telescopes will for the time being keep their current receivers, which offer a broad frequency range. In 2015 we installed a brand-new DBBC (Digital Baseband Converter), to ensure that the VLBI data (Very Long Baseline Interferometry) can be linked to JIVE. VLBI is a technique, based on the simultaneous observation of an object with multiple radio telescopes spread all over Europe and the world. The maintenance of the telescopes was planned and implemented in such a way that no interruption has taken place in the VLBI observations. A compliment to the team!
The Radio Observatory department makes cutting-edge observational facilities and data available to researchers around the world. Continuous development of new observing modes and analysis tools keeps the telescopes attractive for a wide range of astronomers from around the world. The success of our department is reflected in the number of publications of researchers working with it. In the charts below you will find the number of studies conducted using LOFAR, per country.
Until 2014 our department consisted of two groups: Science Support and Technical Operations. In view of the large size and broad range of tasks, in 2014 the latter was split into Operations & Maintenance and Software Support groups. The current three teams consist of a mixed international group, with educational levels that differ from vocational and technical/engineering training to post-PhD levels in physics and astronomy. Science support has a broad international composition.