Antennas and Digital Technology
LOFAR is a collection of radio antennas distributed across Europe. These antennas are controlled by super-computing facilities in The Netherlands in such a way that the entire network acts as a single instrument. The combination of multiple antennas across large distances is known as radio interferometry and it offers the LOFAR telescope far greater power and ability to resolve far-away objects in the sky than any other telescope.
Each international station in the network (including I-LOFAR) consists of an array of antennas, very much the same as radio receiving antennas used in communications broadcasting. LOFAR consists of two types of antennas; the low band antennas (LBA) operating at 10-90 MHz and the high band antennas (HBA) operating at 110-250 MHz. The LBAs can be seen in the picture below and they consist of four copper wires connected to a receiver at the top of a pole and anchored into the ground. Below the LBA a metal mesh is placed which acts as a mirror reflecting radio waves into the copper wires.
The HBAs are more complex antennas which are encased in a styrofoam frame. Each group of 16 antennas are covered by black tarp to form a tile as seen in the image below.
Low Band Antennas
High Band Antennas
The operation of each antenna is controlled by a collection of integrated circuits known as a field programmable gate array (FPGA). The operation of the system by such digital electronics mean that the antennas can be pointed (or beam-formed) electronically to receive from a desired direction. This means the antennas themselves do not need to be moved. Digitally steering a collection of antennas in this way is known as ‘phased array’ technology. The benefit of such technology is that LOFAR can be pointed in many directions at once, acting as a “fly’s eye on the sky”.
Once the signals from all antennas in a station are recorded the data is sent by a high speed (3 Gb/s) fiber optic link to computing facilities in The Netherlands. Data from all LOFAR stations is then processed by a cluster of graphics processing units (GPUs, as seen in the image below) and the data products are stored for future analysis in the Long Term Archive (LTA).
Graphic Processing Units in The Netherlands
The interdisciplinary approach of LOFAR LOFAR has already stimulated discussions between scientists and engineers across Europe to collaborate on this interdisplinary project. Of particular interest to the I-LOFAR consortium is research in:
- Distributed Sensor Fields
- High-speed data communication and GRID computing
- Algorithms for data analysis and visualization
- Use of supercomputers and novel computer architectures
Following significant investment in ICT by Irish funding agencies, such as SFI and Enterprise Ireland, these are areas in which Ireland has great expertise. LOFAR will challenge Irish researchers in ICT to develop new methods for transporting, storing and processing large data volumes, technologies key to the development of the next generation internet. Indeed, IBM are already working closely with LOFAR teams in Sweden and The Netherlands.
The huge ratio between the LOFAR field-of-view and the resolution provided by it’s long baselines represents a huge challenge to traditional imaging and data calibration algorithms. Significant development and innovation will be required to image the entire field-of-view at full resolution, as well to provide adequate calibration and removal of atmospheric effects on long baselines. The broad frequency coverage and narrow channel widths will also present new and exciting possibilities to spectral and polarization studies, which are currently unfeasible for existing telescopes. The consortium is develop statistical imaging reconstruction techniques, focusing in particular on Bayesian and multi-scale techniques.
The I-LOFAR International Station
LOFAR is made up of core, remote and international stations, differing mainly in the number of LBA and HBA antennas in each. I-LOFAR is now a full international station (similar to the one shown above), meaning it consists of 96 LBA antennas and 96 HBA antennas, laid out in a field in the arrangement shown below. Each antenna has two coax cable, buried in cable trenches across the site, with each cable connecting back to a unique receiver board. The station digital electronics (receiver boards and high speed internet link) are housed in a shipping container close to the antennas array. On site at the I-LOFAR station there is also a new Education Centre which can accommodate meetings, small conferences or school children, see an architect’s design below.
The International LOFAR Telescope
The entire collection of international stations, comprising of remote and core stations is known as the International LOFAR telescope (ILT). This consists of 12 “International Stations”, with 5 in Germany, 3 in Poland, and 1 station in France, Sweden, the UK, and now Ireland, shown on the map below. In the Netherlands there are the remote stations and a central core of six stations known as the ‘Superterp’ (in the photo above), made up of the 2×48 LBA dipoles, and 2×24 HBA tiles, and also 24 “core stations” made up of 2×48 LBA dipoles, and 2×24 HBA tiles, and 16 “remote stations” made up of 2×48 LBA dipoles, and 48 HBA tiles.
The Netherlands Institute of Radio Astronomy (ASTRON) is home to LOFAR operations, where LOFAR observing schedules and overall operations are carried out. The University of Groningen in the Netherlands also provides data processing service for LOFAR, with the data processing facility being located in the the ‘Zernikeborg’ building shown above.
Supporters
Birr Kids Space Ireland
Birr Scientific & Heritage Foundation
Grant Engineering
Joe Hogan (Openet)
Dermot Desmond
Denis O’Brien
Birr Lions Club
Birr Chamber of Commerce
Funders
Science Foundation Ireland
Enterprise Ireland
HEAnet
Dept. of Jobs, Enterprise, and Innovation
Offaly County Council
Dept. of Arts, Heritage, Regional, Rural, and Gaeltacht
Dept. for Communities
Consortium Members
TCD
Armagh Observatory and Planetarium
UCD
DCU
UCC
NUIG
DIAS
AIT
Location
Birr Castle Gardens & Science Centre
Rosse Row, Birr,
County Offaly,
R42 VO27
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