Making the array fit for the next decade

Fig. 1: Uniboard2 electronics boards have been selected to replace the digital back-ends, which have been operational in the LOFAR system for the last ten years. Image: ASTRON.

The LOw-Frequency ARray (LOFAR) is now 10 years in continuous operation and has revolutionized the field of radio astronomy at low frequencies (<150 MHz). Year by year its data allows the radio astronomers to produce first rate publications with scientific highlights, covering a diversity of research areas. Studied are meteorological phenomena on Earth,  the Sun's activity, high-velocity outflows from young stars and galaxies, magnetic fields in galaxy cluster to name a few.

As a new generation 'software' radio telescope, LOFAR's main characteristics are the electronics, the high-speed data transport and the sophisticated software, which combine the more than 50 LOFAR stations (antenna fields including local signal processing equipment) spread over Europe to work as a giant camera recording the meter-long radio waves from all over the Universe. The performance of LOFAR is continuously increasing as more stations are added, but mostly by updating the technological infrastructure at the stations, the central processor technology and the software. This is very similar to the progress in computer technology, where the real progress is not so much with the casings of standard desktop computers, but with the performance of the processors and mass-storage devices inside. LOFAR's capabilities can be augmented by taking advantage of new or improved technologies as well as of new software tools. They need to be implemented, if astronomical research with LOFAR is expected to deliver cutting-edge results also in future.

German research interest cover a wide range of scientific topics involving the search for radio galaxies in the young universe, the characterization of (clusters of) galaxies, cosmic-ray propagation, search for radio emitting exoplanets and ultra-fast spinning pulsars, studies of transient phenomena, space weather research, and highly accurate ionosphere studies.

LOFAR 2.0 is a bundle of projects to upgrade the LOFAR stations and to increase the capabilities of the array by advances software tools:

  • New electronic boards (Fig. 1) are developed which will triple the processing power at the stations. This will enable all antennas to be used at once during observations, instead of observing either with the low-band (LBA: 30-80 MHz) or with high-band (HBA: 120-150 MHz) array. This practically doubles the available observing time and consequently the amount of data produced per time unit.
  • At the stations, the clock system will be upgraded to improve the time synchronization of the stations. Improvements by a factor 10-100 are expected. LOFAR measures differences between the arrival times of signals at the different stations and the accuracy of these measurements governs the quality of the images.
  • A major software development effort will be made to use the German and other international stations with an order of magnitude higher efficiency. Currently observations including the full LOFAR array require heavy human intervention during image construction, which will be replaced by a largely automated pipeline data reduction process.
  • New software is developed to allow efficient data processing with the HBA and LBA observing in parallel. The quality of the images obtained especially at LBA frequencies is strongly degraded by the fluctuations of Earth's ionosphere (Fig. 2). Parallel observations will improve the sensitivity for the LBA array by a factor of five.

LBA observation image construction. Left: The image is still corrupted by ionospheric errors. Center: same region after direction-independent calibration, where the bulk of the ionospheric corruptions are removed (5 mJy/beam rms noise; beam: 45"). Right: the final correction after detailed modelling the ionosphere in multiple directions (1 mJy/beam rms noise; beam: 20"). Image: F. De Gasperin.


The German contribution to LOFAR 2.0 will be the electronics upgrade of the six German stations starting in 2022 and a heavy investment in software development in areas as low-band imaging in general, joint solar observations with space probes and expanding the data archive capacities and processing capabilities.