URSI Commission J (Radio Astronomy) Report to CNC

April 2003

D. Routledge, Canadian Commission J Chairman
[Dept. Electrical Engineering, Univ. of Alberta, Edmonton, AB T6G 2V4 Canada]

The mandate of URSI Commission J includes the promotion of technical means of radio astronomical observations and data analysis, support of activities to protect radio astronomy from harmful interference, and the observation and interpretation of celestial radio emissions. URSI and the conferences it organizes constitute an important channel for technical communication among the radio astronomers of the world, and between them and other users of the electromagnetic spectrum. It is essential to the continued development and protection of Canadian radio astronomy that the Herzberg Institute of Astrophysics continue to support [the Canadian National Committee of] URSI financially.

Canadian radio astronomers' involvement in URSI is important today because they are deeply involved in the development of the world's next generation of instrumentation for radio astronomy, and because radio astronomy's access to the electromagnetic spectrum continues to be threatened. The Canadian Commission J membership is split roughly equally between persons who observe with radio telescopes or use radio data but do not have direct involvement in improvement of instruments and techniques, and those who do. On the other hand, within the "technically involved" group, roughly half do not themselves make astronomical observations or interpret radio data for astrophysical purposes. Canadian expertise in radio astronomy resides primarily within the Herzberg Institute of Astrophysics, but of course radio astrophysical expertise and activity extend into many Canadian universities, large and small. [... M]any profoundly innovative developments in astronomical instrumentation come from persons who have deep understanding of the technical principles and problems, but who are also involved in active astronomical research and driven by the needs of the science which the instruments are created to satisfy.

RADIO ASTRONOMICAL FACILITIES

The most important development in Canadian radio astronomy in 2002/2003 was allocation by the federal government of funding for ALMA and for the EVLA correlator development. This funding marks approval at the highest level, of projects which received consensus backing from the entire Canadian astronomical community in the process of development of the Long Range Plan for astronomy.

A. ALMA

The Atacama Large Millimeter Array, will be situated at 5000 metres altitude in the Chilean Andes. It will be an international mm/submm aperture synthesis telescope with sixty-four 12-metre antennas providing high sensitivity, high spectral resolution, and very high angular resolution, initially in four dual-polarization bands between 84 and 720 GHz. ALMA is currently a two-way partnership between a North American consortium (the U.S. and Canada) and a European consortium, but it is likely that Japan will also enter as a third partner, allowing the performance of the array to be enhanced.

The technical design of the array is very far advanced and civil infrastructure construction will begin in late 2003. Three prototype 12-metre antennas (U.S., European, and Japanese) of competing design have been produced. Canadian technical involvement in the project is concentrated in receiver development for Band 3 (84-116 GHz) at HIA Victoria, software development and data archiving, and phase correction systems. A Canadian astronomer from the university community (C. Wilson) chaired the ALMA Science Advisory Committee for the past six months. Another Canadian (C. Cunningham) from HIA served as team leader for receivers.

The Very Large Array Expansion project (EVLA) is a joint enterprise among the U.S., Canada, and Mexico. Canada's participation in the EVLA project is part of the North American Partnership for Radio Astronomy Agreement (NAPRA), and it is because of the existence of NAPRA that Canada can be involved in the ALMA project. The aim of the EVLA project is to increase the capabilies of the VLA about 10X in continuum sensitivity, over 1000X in spectral resolution, and by several times in angular resolution. The VLA's wavelength coverage will also be extended shortward to 7mm. The heart of this ambitious program is the development of a hugely improved digital correlator at DRAO. The DRAO "WIDAR" concept is the key to the innovative EVLA correlator design; without it the correlator would have used conventional techniques as originally planned by NRAO, and would have been less flexible and less powerful. The WIDAR concept originated with Brent Carlson of HIA. NRAO expects the first scientific observations to be possible with the new DRAO correlator in 2007, and plans to decommission both its existing VLA correlator and its existing Very Long Baseline Array (VLBA) correlator when the WIDAR correlator is fully operational in 2009.

The work underway at DRAO by the team designing the EVLA correlator will in turn provide a springboard for even more advanced systems, including the digital beam-forming and correlation system for the Square Kilometre Array (SKA) project.

B. SKA/LAR

Canada has had a leading role from the outset in the international Square Kilometre Array (SKA) project. For high sensitivity, the SKA will require about 100X the collecting area of the VLA. However, the SKA will also deliver angular resolution of milliarcseconds as an aperture synthesis telescope, with baselines stretching hundreds of kilometres. Each of perhaps thirty antennas must therefore contribute huge collecting area for sensitive cm/dm - wave spectroscopic imaging. Canada's candidate in the competition to determine the technology of the large-area antennas is the Large Adaptive Reflector (LAR) concept, which originated with Tom Legg of HIA. This is an adjustable offset-feed paraboloid mounted nearly flat on the ground for low cost, with reflecting panels controlled by actuators so that the antenna profile can be continuously adjusted to track objects in the sky. A long focal length (500m) is required to keep actuator throw minimal and cost low. The feed will therefore be carried under a multiply-tethered aerostat. The LAR concept is being developed by a Canadian NRC/university/industry consortium.

A 1/3-scale tethered aerostat is now flying at DRAO. This is being used to determine the feasibility of an airborne platform and understand its behaviour through refinement of computer models. A 20 metre helium aerostat has been purchased and modified, specialised ground-handling equipment and techniques have been devised, and a GPS-based tether-confluence-point measurement system is under study. Winches are now being installed, and a multiple-tether control system is being designed.

The prototype Large Adaptive Reflector will be an exciting and versatile astronomical instrument in its own right. As a fully-steerable unblocked-aperture telescope of great sensitivity and moderately high angular resolution, it will be extremely useful in Galactic and extragalactic spectroscopic programs, pulsar studies, VLBI observations, etc., in exactly the way that the Effelsberg 100-metre telescope and the recently commissioned 110-metre Green Bank Telescope are useful. Design work is underway within the Canadian LAR consortium on a variety of LAR subsystems including reflector panels and actuators, receivers, control systems, and broadband focal-plane antenna arrays (PhD project, E.Reid). It is immensely important that the LAR concept be sufficiently mature technically that it can survive the "down- selection" of SKA technology concepts which is scheduled to occur in 2005.

Through aperture synthesis, broad spectral coverage, and huge collecting area the SKA will give imaging access to large portions of the Universe in redshift, from before the advent of galaxies to the present. The actual construction of the SKA will occur after ALMA. The international SKA consortium currently consists of 14 countries plus 3 more countries which send only official observers to meetings of the International SKA Steering Committee (ISSC). Canada has two members on the ISSC, one from within HIA (P. Dewdney) and one from within the university community (R. Taylor). Canada also provides three members of the SKA International Science Advisory Committee (S. Cote, S. Dougherty, and R. Taylor) and a member of the International SKA Engineering Management Team (B. Veidt). The 2004 international SKA meeting will be hosted by Canada. A Canadian SKA Steering Committee has been formed by the CASCA Radio Astronomy Committee.

C. JCMT

HARP (Heterodyne Array Receiver Programme) is a 16-element focal-plane array of antennas for the JCMT Nasmyth focus, with receiver front-ends for the 350 GHz atmospheric window. It is being built at Cambridge, UK, with contributions from HIA. In combination with ACSIS it will place 16 beams on the sky, and each beam will produce a multichannel spectrum.

The Auto-Correlation Spectrometer Imaging System (ACSIS) is being developed to produce calibrated spectra from the focal plane array of sixteen 345 GHz HARP receivers. These spectra will appear at the rate of 20 per second, ready for gridding and display in real time. The correlator hardware has been developed at DRAO (T. Burgess) and is complete. The samplers, which convert the sixteen 345 GHz analog signals into digital streams, are also being readied at DRAO. The IF system is advancing, with the Down-Converter Module being built by Murandi Communications of Calgary. The ACSIS reduction software will run on an array of dual-processor Linux computers. Final integration and commissioning of the ACSIS system is to occur at the end of 2003.

SCUBA-2 will be a bolometer array far surpassing the current Submillimetre Common User Bolometer Array (SCUBA) in sensitivity and number of beams on the sky. The current SCUBA produces 37 beams in a 5 arcmin2 field of view for continuum observation in the 750 and 850 (m atmospheric windows. SCUBA-2 will produce ~30,000 pixels in a 64 arcmin2 field of view at 850 and 450 (m. SCUBA-2 will be accompanied by a polarimeter and a Fourier transform spectrometer.

The interconnection between the JCMT and the 8-element Smithsonian Millimeter Array at 4000 metres on Mauna Kea will give Canadians access to a high-altitude aperture synthesis array before ALMA is available. The JCMT in turn will increase the sensitivity of the SMA. 183 GHz heterodyne water-vapour radiometers and a 20-micrometres infrared water-vapour bolometer radiometer (U. Lethbridge) have been tested on Mauna Kea for use in antenna-based sub-mm phase correction.

D. Space VLBI

The Japanese satellite HALCA, which carries a sophisticated VLBI receiving system in its eccentric orbit, continued to make 5 GHz observations of high-brightness objects in cooperation with ground telescopes. Almost all the recent VSOP observations have been correlated at the S2 correlation centre at DRAO. (The S2 VLBI recording and playback system was developed in Canada, primarily at CRESTech.) The observations were analysed at the VSOP data analysis centre at the University of Calgary. However, the VSOP Survey project, i.e. systematic observations of radio-bright quasars and AGN, will end in 2003. Canada is now planning for future SVLBI missions including VSOP-2 and I-ARISE. In addition, the Russian Space Agency has assigned the Radioastron space VLBI mission (an orbiting 10m antenna and 22 GHz receiving system) the number one priority position in the Russian space astronomy program. The launch is scheduled for 2006 and apogee will be near 340,000 km, so that the angular resolution will be unprecedented. The Canadian space VLBI program was originally started to support the Radioastron project, and we may hope that Canada will take part in the reborn project in 2006.

E. ODIN

Odin is a satellite for radio astronomy and aeronomy which was launched in 2001. Canada is an international partner in this project with Sweden, Finland, and France, and contributed an instrument called the Optical Spectrograph and InfraRed Imaging System (OSIRIS). The spacecraft is astronomically important because of its ability to detect H2O and O2 molecules (key molecules in star formation) in the ISM, among others. It carries a 1.1-metre-diameter radio telescope with cooled heterodyne receivers in five bands from 118 to 580 GHz, and performs on-board spectrometry. The angular resolution of this telescope is as fine as 2 arcminutes. Canada also contributed the cryogenic cooler for the mm/sub-mm receivers.

Odin is mapping H2O in several molecular clouds and comets, and achieved the first detection of the ground-state transition of ammonia. It s continuing to search for molecular oxygen in the ISM.

F. DRAO

The Synthesis Telescope at DRAO continues to fill a valuable role in steadily producing high-quality data for the Canadian Galactic plane Survey (CGPS), as part of the International Galactic Plane Survey (IGPS). The CGPS data set consists of high-dynamic-range mosaiced continuum and polarization 1.4 GHz images and 256-channel spectroscpic 21cm HI images, all with ~1-arcminute resolution, plus 0.4 GHz continuum images with ~3.5-arcminute resolution. The fidelity of the very wide-field continuum and HI mosaics is unsurpassed because of the careful inclusion of low-order Fourier components from single-dish telescopes such as the DRAO 26 metre telescope and the Effelsberg 100m telescope.

It is important to note that the venerable 26m DRAO telescope is actually playing a vital role in providing carefully calibrated and sidelobe-corrected low-resolution 21cm spectra for inclusion in the Synthesis Telescope HI mosaics. Somewhat amazingly, the 26m telescope is also being used to provide fiducial polarization survey data (M. Wolleben, PhD student) for the 1.4 GHz polarization mosaics, which will be used as fundamental data to which the polarization observations made with the Effelsberg 100m telescope can be anchored. The Effelsberg data in turn will constitute the lower-order Fourier components of the ultimate mosaics of polarized emission produced by the Synthesis Telescope and the 100m telescope together.

The IGPS continues the objectives of the CGPS, mapping the atomic, relativistic, and ionized components of the ISM with arcminute resolution, and extends it to imaging most of the plane of the Galaxy. Data are being provided by DRAO (northern declinations), the Australia Telescope (southern declinations), and the Very Large Array (equatorial declinations). CO survey data are being contributed by the Onsala and FCRAO mm-wave telescopes.

The sensitivity of the Synthesis Telescope itself is currently being improved by identification and reduction of sources of antenna noise (MSc project, T. Ng) and reduction of receiver noise (MSc project, A. Garcia). Ng's MSc project also includes calculation of instrumental polarization across the Synthesis Telescope's field of view.

A hugely important development at DRAO in 2002 was the completion of the new observatory building, and removal of many of the disintegrating trailers in which these widely admired and respected scientists worked for so many years. The effect on observatory morale has been marked, and international visitors to one of Canada's most productive scientific institutions are no longer apalled.

INTERFERENCE PROTECTION:

Geography and terrain no longer protect radio observatories adequately against interference. Instead, radio astronomy must now depend on the interference controls set by the International Telecommunications Union and the regulatory arm of Industry Canada. A band-by-band international interference protection study, initiated by the satellite communications community, is now under- way to examine the specific protection requirements of radio astronomy. K. Tapping and P. Feldman (HIA) are working with their international colleagues on radio astronomical band requirements above 275 GHz. However, adjacent-band spillover from satellite-borne transmitters can easily render even a long-protected radio astronomy band useless, as Sky TV has done to the 10.6-10.7 GHz band in Europe. Similarly, the satellite broadcasting service has been allocated the band immediately below the 42.5-43.5 GHz band, which contains the SiO line.

Progress is being made, however, in that interference levels can now be quantified in terms of degradation of observational data if picked up in radio telescope sidelobes. Levels are identified for both continuum and spectral line observations, and these are being upgraded to include radio astronomy bands above 71 GHz for presentation at the 2003 World Radio Conference. A proposal being prepared includes a modelling process using a generic radio telescope beam. This will allow calculation of the interference levels to be expected by radio telescopes from a given communications satellite constellation before any of the satellites are launched.

The international band-by-band study continues. Radio astronomical spectrum needs between 71 and 275 GHz were defined at the 2000 World Radio Conference, and the needs above 275 GHz are now being examined. The international radio astronomy lobby is becoming more tightly-knit, and Industry Canada is becoming more aware of the constraints imposed by nature on radio astronomy. However, next-generation telescopes such as ALMA and the SKA will need to have International Radio Quiet Zones established around them, to allow them to operate close to their sensitivity limits over as much of the spectrum as possible. Such an idea is certain to be opposed by the international satellite communications lobby.

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