The Low Frequency Array, the world's largest distributed radio telescope

The Low Frequency Array, is a multi-purpose sensor array. Its main application is astronomy at low radio frequencies (10-240 MHz). LOFAR consists of an array of antenna fields distributed throughout the Netherlands and several neighbouring countries. The maximum resolution of an telescope is determined by its diameter. The largest single dish radio telescopes have diameters of several hundred meters at most. Radio interferometers combine the signals of several single dish telescopes to achieve a resolution higher than possible with single dish.

With the advances in information technology, it is for the first time possible to fully process the signals of radio interferometers operating at low radio frequencies with digital electronic components. LOFAR is the first telescope which utilizes digital components for real time processing of the signals in a large telescope array.

Instead of dishes LOFAR uses arrays of dipole antennas. This allows to achieve a large collecting area for radio waves for each of the elements of the radio interferometer. Those phased arrays still have a pointing direction (similar to a dish), however, phased arrays can point to several directions at the same time, in contrast to dishes. 

LOFAR consists of 37 stations in the Netherlands, six stations in Germany, three in Poland, one station in France, UK, Sweden and Ireland each. The signals of the LOFAR stations are transferred to a central processing unit via high speed internet connections. Each station can send data with a rate up to 4 Gibabyte per second. The signal of all stations needs to be processed (correlated) in real time for an interferometric observation. This requires fast and reliable network connections and very fast central processing unit with very high input and output rates. Recently, a dedicated GPU-cluster has been developed for this task. 


Further Reading:

Überblick und Funktionsprinzip des LOFAR Radioteleskops (in German)

The LOFAR 2.0 project - A LOFAR upgrade

LOFAR page at ASTRON, the Netherlands Institute for Radio Astronomy (Astron web pages)

LOFAR in the 'Landschaft der Forschungsinfrastrukturen' of the German Federal Ministry of Education and Research (BMBF web pages)