Offaly County Council confers Civic Recognition Award on Professor Peter Gallagher

Press Release from Offaly County Council:

Professor Gallagher received the award at a Civic Reception in Offaly County Council on Monday, 16th October 2018. The special event was attended by Professor Gallagher’s family, colleagues and guests from the worlds of science, academia, tourism, enterprise and local development. Among the guests were Lord and Lady Rosse, Lady Alicia Clements of Birr Castle, and Mr. Joe Hogan of Openet.

At the Civic Reception, Offaly County Council Cathaoirleach Cllr. Danny Owens informed the attendees that the decision to confer a Civic Recognition Award is a reserved function of Offaly County Council. It is an acknowledgement of a person’s outstanding contribution to the County.

The Civic Recognition Award acknowledges Professor Peter Gallagher’s outstanding contribution to the County; leading the €2m I-LOFAR project in Birr, developing the I-LOFAR Education Centre in conjunction with Offaly County Council, and for on-going work to develop collaborative research and discovery in Offaly.

Cathaoirleach Cllr. Danny Owens spoke of Birr’s rich astronomical heritage, a worldwide reputation that is a great source of pride for Offaly people. The selection of Birr as the location for the new I-LOFAR radio telescope marks a new chapter for scientific endeavour in Offaly.

I-LOFAR is the Irish Station in a European wide network of state-of-the-art radio telescopes. The telescope is used to study celestial objects such as the sun, black holes and magnetic fields.

In addition to the benefits of having a cutting-edge science project in Offaly, having the I-LOFAR telescope in Birr opens up new possibilities for research, jobs, tourism and science education.

Offaly County Council’s Chief Executive Ms. Anna Marie Delaney acknowledged Professor Gallagher’s willingness to collaborate and work with Offaly County Council and others to harness the economic potential of I-LOFAR. Ms. Delaney outlined a number of projects where Professor Gallagher had generously given of his time, including the development of the I-LOFAR Education Centre and a field trip to ASTRON (the Netherlands Institute for Radio Astronomy).

Professor Gallagher then gave an informative and engaging presentation on the I-LOFAR project and the opportunities for further development. Elected Members Cllr. John Carroll and Cllr. John Clendennen commended Professor Gallagher’s enthusiasm, work to date and drive to develop scientific discovery in Offaly.

Offaly County Council Cathaoirleach Cllr. Danny Owens then presented Professor Gallagher with a framed scroll and a specially commissioned piece of art to commemorate the Civic Recognition. The commissioned piece was designed and produced by LEO Offaly client Michelle O’Donnell of Glasshammer Studios. Radio images generated from the I-LOFAR telescope were used as inspiration for the piece.

MC and Director of Services Mr. Frank Heslin thanked all present and invited all to join the Members for refreshments in the Council atrium.

I-LOFAR is operated by Trinity College Dublin on behalf of the I-LOFAR Consortium. It is supported by Science Foundation Ireland, the Dept of Business, Enterprise and Innovation, Offaly Co Co, and many others.

Station Signal Processing Pipeline

1. Antennas

LOFAR station is a wide-band radio receiver, which operates at the frequency range from 10 MHz to 240 MHz. The full reception band is divided into low band (10 MHz – 90 MHz) and high band (110 MHz – 240 MHz). The frequencies in between low band and high band are not used due to RFI from FM radio transmitters.

The station signal processing has been originally designed assuming that three different antenna arrays would be used. These arrays would have been the low-band-low (LBL) antenna array, the low-band-high (LBH) antenna array, and the high-band antenna (HBA) array. However, the present standard stations do not have the LBL antennas, and the LBH antenna array is thus referred to as the low-band antenna (LBA) array.

Antennas used in LOFAR stations are briefly introduced in following two sections. Notice that the antenna array configurations are configurations of full antenna arrays. It is always possible to manually select only a subset of a full antenna array to be used e.g. in beamforming. Positions of individual antenna elements and antenna array definitions of a station are stored in station configuration files.

2. Receiver Control Units (RCUs)

The analogue signals from LBA elements and HBA tiles are transferred in coaxial cables to a LOFAR station cabinet, where each of the cables is connected to a receiver unit. A RCU performs input selection, followed by amplification and filtering of the analogue input signal. The conditioned analog signal is sampled with a 12-bit A/D converter. The A/D converter produces real signal samples at either 200 MHz or 160 MHz sampling frequency. Combinations of filter passband and sample clock frequency are selected so that the selected frequency band always aliases around zero frequency, without frequency aliasing inside the passband. With one of the available combinations the signal spectrum will be inverted, but it can be inverted back in subsequent processing steps.

The receiver units are numbered starting from zero. X-polarisation cables are connected to even-numbered RCUs and Y-polarisation cables are connected to odd-numbered ones.  The only deviation from this rule is the LBA outer field, whose X-polarisation cables are connected to odd-numbered RCUs and Y- polarisation cables to the even-numbered ones. A receiver unit has three inputs: LBL, LBH, and HBA. The LBL and LBH connectors have an 8 V bias voltage. The HBA X-polarisation connectors have the 48 V bias voltage for power supply. The HBA Y-polarisation connectors have a 3.3 V bias voltage only when communicating with the HBA tiles.

A core station or a remote station with 96 LBA elements and 48 HBA tiles has 96 RCUs. The LBA inner array is connected to the LBH inputs and the LBA outer array to the LBL inputs. Despite the naming convention in RCUs, both LBA inner and LBA outer use the same kind of antenna elements. The HBA tiles are connected to the HBA inputs.

Due to their larger number of HBA tiles, international stations have 192 RCUs. The 96 LBA elements of an international station are connected to the LBH inputs of the RCUs, and the 96 HBA tiles are connected to the HBA inputs. In a basic installation of an international station the LBL inputs are left empty, thus facilitating later installation of an additional antenna array.

3. Remote Station Processing Boards (RSPs)

After frequency band selection and A/D conversion in the RCUs, the received signals are transferred to remote station processing boards. The RSP boards perform all digital signal processing that is done at the station, and send data to central processor (CEP).

The discrete signal samples arriving from a RCU to a RSP board are first buffered in a FIFO buffer. In order to compensate for differences in signal delays in the coaxial cables, buffer length can be adjusted independently for each individual RCU. The buffer is followed by a polyphase filter, which divides the wide band input signal into so-called subbands.

A polyphase filter is a novel FFT-based implementation of a bandpass filter bank, which divides the real input signal into 1024 complex subband signals. Because the real input contains two identical (mirrored) copies of the signal spectrum – one at positive and the other at negative frequencies – the lowest 512 subbands are complex conjugates of the 512 highest ones. The whole receiver passband is thus covered by the 512 lowest subbands, which are used in further processing. Depending on sample clock frequency, subband width is either 200 MHz/1024 = 195.3125 kHz, or 160 MHz/1024 = 156.250 kHz.

After the polyphase filter the signal bandwidth is small enough to facilitate phased-array beamforming1, which produces beamformed subband signals called beamlets. Although 512 subbands are produced in the polyphase filter, only 244 beamlets can be formed by the station signal processing. Subbands used in beamforming are selected immediately after the polyphase filter. The beamforming is performed in a ring, where a process handling signal from one RCU receives a partial beamforming result, adds the contribution from its own RCU, and passes the result forward to the process handling signal from the next RCU. In order to facilitate the beamforming, the RSP boards of a LOFAR station are connected together as a ring. After a full cycle in the ring, the beamformed sample is complete and ready to be transmitted to central processing.

The beamforming ring is divided into four separate lanes, each of which has its start and end point in a different RSP board. Beamformed data are output from those RSP boards that are endpoints of the beamforming lanes. In core stations the beamforming lanes can be split into two halves, allowing independent beamforming with the HBA0 and HBA1 arrays. Because 244 beamlets can be formed with both arrays, the splitting allows core stations to form 488 beamlets simultaneously, but each of them with only 24 HBA tiles. Four additional output RSP boards are defined in the split mode, i.e. data are being output from eight RSP boards simultaneously.

In addition to the beamforming, the RSP boards can calculate so-called subband statistics , beamlet statistics , and array covariances (crosslet statistics) . Likewise the beamlets, the co- variances are also formed in the ring of RSP boards, and their calculation is divided into four lanes. All these crosslet lanes start from and end to the same RSP board, which also outputs the data. The crosslet output board is usually different from the beamlet output boards. The RSP boards can also send either raw A/D converter samples or subband data to ring buffers in transient buffer boards.

An RSP board has four antenna processors (AP). Each AP processes two orthogonal polarisations from its connected antenna. Each RSP board thus has 8 digital inputs for the signals from the RCUs, which defines the number of RSP boards in a station: core stations and remote stations have 12 RSP boards, whereas international stations have 24 RSP boards.

4. Transient Buffer Boards (TBBs)

Transient buffer boards are not part of the main signal processing chain, but their function is to store a short period of raw voltage data in a ring buffer. Writing to the buffer can be stopped when a triggering event is detected, after which the data can be read from the buffer.

TBBs are physically connected to the RSP boards, which provide the raw data that is buffered to the boards. Two kinds of data can be buffered: in ”transient” mode real signal samples are copied to TBBs immediately after the FIFO buffers in RSP boards, whereas in ”subbands” mode complex subband data produced by the polyphase filter are copied to the TBBs. TBB memory is divided into pages, which are large enough for 1024 12-bit data samples in ”transient” mode. Because the subband data is in 16-bit format, only 487 of the 512 subbands can be recorded in ”subbands” mode.

One TBB is capable of recording data from 16 RCUs, and each TBB is thus connected to two RSP boards. Core stations and remote stations thus have 6 TBBs, whereas international stations have 12 TBBs.

5. Local Control Unit (LCU)

Local Control Unit (LCU) is a computer running the Redhat Linux OS. All station control happens via the LCU, which runs a number of control processes that communicate with the different processing boards of the station. LCU also receives station clock signals from GPS and a rubidium standard. Users can log on to the LCU via a ssh connection, and control the whole station from the command line. Single-station control is covered in more detail in Section 3, and relevant commands are listed in the command reference.

Back to the I-LOFAR Observer’s Guide

Opinion: Ireland should be at forefront of modern science – Ireland should join CERN

TURN ON YOUR television, or your radio, and tune it to an empty station where you can’t receive any signal. See all those black and white dots scattering around the screen, or hear that faint hiss in the background? A part of that is a radio signal from the universe, namely the Cosmic Microwave Background radiation, the heat energy left over from the Big Bang itself.

Light at radio-wavelengths is emitted by all kinds of celestial bodies: stars, galaxies, planets, and more. Visible light that we use “normal” telescopes for only gives us part of the picture, whereas radio astronomy opens up an entire new spectrum of the universe we are otherwise blind to.

The full article can be read here.