Report of the International Review Panel for the MERLIN/VLBI National Facility


The review was carried out on 25 - 27 September 2000. The Panel members were M. Goss (Chair), A. Baudry, R. Hills and K. Menten.

The Panel thinks that the National Facility (NF) plays a significant and unique role in current observational astronomy. The astronomical topics for which its high resolution is relevant cover a wide range, from cosmology to galactic stars.

The restructuring of the facility since 1997 has resulted in the desired savings and has had positive effects. The appointment of a Director (initially internal and later from the outside) has worked well. The increased usage of the NF by outsiders is encouraging.

The budget has, however, been eroded due to the lack of indexation in the past and is not really adequate to support the agreed programme. Medium-scale improvements to Facility are not possible within the current budget.

The e-MERLIN proposal will provide a unique facility for high resolution cm-wave astronomy for at least ten years if it is begun in the next few years. It will increase the sensitivity and frequency coverage, so that a wide range of new astronomical projects can be undertaken.

The NF continues to play a key role in the European VLBI Network. The interactions between the JIVE correlator design and implementation and the NF have been productive.

The synergy between the University of Manchester astronomers and the National Facility is an important asset. This combination of expertise will insure that the UK remains a centre of excellence in interferometry that will play a significant role in ALMA and SKA in the future.


The review was carried out at the request of the Facility's Steering Committee. The members were Miller Goss (NRAO, USA -Chair), Alain Baudry (Bordeaux, France), Richard Hills (Cambridge, UK), and Karl Menten (MPIfR-Bonn, Germany). The Panel met at the Jodrell Bank Observatory on September 25th to 27th. They received presentations from both the National Facility director and the Jodrell Bank Observatory director, covering the organisation of the Observatory and the operation of the Facility, followed by a tour of some of the facilities.

They were then given a series of talks on scientific results obtained with MERLIN and by VLBI from members of the Facility staff, from Manchester University staff and from external users. Two of the seven presenters were from external UK institutes. There was then a discussion session with the presenters. The Panel is most appreciative of the time and effort given by these astronomers (especially those who travelled from outside) to make presentations and to give us their views.

On the second day the plans for upgrading the facility were presented by the Director, Phil Diamond. These included the on-going upgrade to the Lovell Telescope, other small- and medium-scale enhancements and the major upgrade to the Facility called "e-MERLIN". The key elements of the e-MERLIN project are: the replacement of the radio links between the telescopes by optical fibres giving an increase in bandwidth of a factor of ~100; a new high-bandwidth correlator; new receivers giving much wider frequency coverage; and the replacement of the antenna at Defford with a new 25-metre dish so that a full set of baselines is available at the higher frequencies. These plans were discussed in some detail, along with future plans in the VLBI area and other possibilities, such as the idea of a 32-metre antenna in Ireland which would be linked to the Facility.

The Panel then undertook a series of discussions with the various groups of staff, including the senior management, the Manchester University staff, the Facility operations staff, the receiver engineers, the mechanical engineers and the computer programmers and managers. The Panel met with about 25 individuals in all. On the final day the Panel reviewed the material and agreed a summary of their conclusions, which were then given to the Director in a brief feedback session.

The Panel is most grateful to the Director and his team for the thoughtful organisation of the meeting, the clear presentations and the opportunity to meet so many of the staff and have detailed and open discussions with them.


We have formulated these as responses to the three points in the Panel's Terms of Reference (attached as annex 1), together with some comments on Very Long Baseline Interferometry:

(i) The international competitiveness of MERLIN, with particular reference to the scientific output and relevance to the astronomical community of the UK:

The Panel believes that MERLIN does play a significant and valuable role in current observational astronomy. Its key capability is of course the extremely high angular resolution that it achieves over more than four octaves of wavelength. The fact that this resolution is now being matched by other instruments in different wavebands has greatly enhanced the scientific importance of MERLIN observations. MERLIN provides an angular resolution of 0.15 arc seconds at 1.4 GHz (21cm) and 0.01 arc sec at 22 GHz (1.3cm). It is unique in that it is the only instrument in the world able to achieve this resolution at these wavelengths. The baselines are an order of magnitude larger than the existing VLA, but shorter than those generally used for VLBI. The US National Radio Astronomy Observatory has proposed an upgrade to the VLA (the e-VLA - Expanded Very Large Array) but the first phase of this will only increase the sensitivity, not the baseline length. A second phase, which will provide baselines similar to MERLIN's, is under discussion but has not yet been formally proposed. Work on this second phase, which is likely to cost $70-80 million, will only begin in 2005 or 2006 at the earliest, with operation anticipated from about 2010 onwards.

The astronomical topics to which the high resolution achieved by MERLIN can be applied now cover quite a wide range. They include: cosmology via gravitational lenses and high-z objects; star-burst activity in galaxies; physics of jets in both AGN's and lower-mass analogues; supernova remnants; evolved stars; binary systems; and young stellar objects. Astrometric applications are also significant, e.g. pulsar proper motions and reference frames. The alignment of the Hubble Deep Field with the radio frame is a prominent recent example. The Panel feels that this range of topics is well matched to the interests of the UK community and this is reflected in the fact that the UK users community is now quite widely spread geographically, even though it remains relatively small in numerical terms.

MERLIN provides high sensitivity - the typical noise level is 35 to 70 microJy on a single 'track' and 6 microJy was achieved on the HDF. It is nevertheless true that much of the current work is sensitivity limited and that in many cases the high angular resolution of MERLIN can only be applied to the brightest objects in a given class. In particular, although it is now possible to image thermal sources, these observations are often at the limit of the current sensitivity.

The Panel reviewed the lists of publications and recent trends. They felt that, in both the number and quality of papers published, the level recently achieved is at the standard expected for such a facility. The best work of the National Facility Staff clearly ranks as first rate and has received considerable attention on the international scene. A number of key astrophysical problems have been addressed in recent work.

The Panel was struck by the large number of outside users. There are roughly 25 UK institutes, 17 European and 17 non-European groups (including 10 in the US) using the National Facility at present.

(ii) The current organisation and operation of MERLIN in relation to its operating budget, and targeting to ensure maximum scientific effectiveness:

At the level of detail to which the Panel were able to investigate, it appears that this is a well-run Facility with an enthusiastic and highly motivated staff.

It was explained that (as a result of a reduction in the support provided by the University and pressures in the PPARC budget), a restructuring of the operation had been undertaken to make it possible to run the Facility within a constrained budget, whilst maintaining the operational targets and scientific output. The Panel formed the impression that, although this has clearly put a lot of pressure on resources and in particular on some of the key people, the restructuring, taken together with other changes in organisation, has had substantial positive effects. In particular the appointment of a Director of the Facility (initially from within the Jodrell Bank staff and now as a new appointment from outside) has clearly worked well. There has obviously been a real effort to increase usage of the Facility from outside Jodrell Bank and to provide outside users with a good service. More flexible ways of working had been found and the scientific output has undoubtedly improved, both in terms of the number of papers and the range of astronomical topics being addressed. The staff had therefore responded well to the challenge with which they had been faced. A continuing effort will however be needed to nurture the community: there is still scope for wider usage of the Facility.

A very positive feature is the synergy between the National Facility and the University of Manchester's astronomers. The combination of expertise residing in the Facility and University staff makes Jodrell Bank a centre of excellence in interferometry at the highest international levels. This is a key resource for future projects such as ALMA and the SKA. The training of students is also of international significance. Many leaders in astronomy throughout the world are former Jodrell Bank students.

In the presentations on the operation it was emphasized that it was proving increasingly difficult to meet the agreed programme within the present budget. It had been eroded by lack of indexation in previous years and, even though an indexation of 2.5% was provided, the real costs now exceeded the budget provided. The level of funding for development of the Facility which had been agreed at the time of the restructuring was also proving quite inadequate to allow any meaningful enhancements.

The Panel looked at the nature of the operation, noting that it requires sophisticated electronics and data processing systems and is distributed, i.e. that equipment has to be supported at quite a large number of remote sites. They also noted that there are several different designs of telescope in the array and that much of the equipment is now quite old. Given this background, the Panel felt that the current costs for operating the Facility were reasonable and that it does appear that the budget is not really adequate to support the agreed programme. At the level of scrutiny that they were able to undertake, the Panel did not see scope for making significant savings without making substantial reductions in the level of operation. It appeared that at present there is perhaps rather more pressure on staff posts (particularly in supporting the observers, scheduling and data processing) than on the cash budget. The Panel were told that there were several areas where the Facility is dependent on the expertise of just one or two individuals. They also noted that staffing in areas like the mechanical and electronic workshops is very small. Unfortunately a number of increases in costs can be foreseen, including increased rental costs of sites and increased charges for the Lovell Telescope, if it is used for more programmes after its upgrade. The Panel also felt that it would not be possible for MERLIN to remain at the forefront scientifically, in even the medium term, unless a higher level of funding for small- to medium-scale developments could be obtained.

Although the Panel is not aware of the detailed terms of reference of the Steering Committee, it felt that oversight by such a body was appropriate. Adding a member from overseas would perhaps be a good idea given the numbers of non-UK users and to bring a wider perspective. The Panel noted that the staff of the Facility seemed to be unclear as to what the mechanisms are that set the level of the annual budget and what opportunities there might be to make applications for e.g. medium-scale enhancements to the Facility.

(iii) Future options and requirements for MERLIN in respect to the likely prospects for radio astronomy in the next ten years:

(1) The upgrade to the Lovell (via a JIF grant) is expected to be complete by the end of 2002. This will provide a new surface and better pointing accuracy, allowing observing at 5 GHz with good efficiency. When operated with the Lovell, and with improved receivers which are now under construction, MERLIN's sensitivity at 5 GHz will increase by a factor of about three. The Panel were confident that this will enhance the scientific productivity of the Facility significantly and ensure that it can pursue a competitive programme for at least 2 and perhaps as much as 4 years. Beyond that time frame, however, it seems likely that the scope for new work will be increasingly limited by lack of sensitivity and MERLIN's capabilities will no longer be well-matched to other facilities, especially the VLA, which by then is expected to have been made broad-band (e-VLA phase 1). It will therefore be essential to provide MERLIN with a much greater increase in sensitivity and to replace some of the older equipment if the Facility is to remain at the scientific forefront for as long as ten years.

(2) The e-MERLIN proposal is of course designed to provide such an increase in sensitivity. For continuum observations the much larger bandwidth should provide a full factor of ten improvement. (There are some concerns about radio frequency interference which will need to be monitored carefully.) It will also make it possible to make images with remarkably large fields of view, given the extremely high resolution. The Panel sees this as an exciting new development. There is a strong scientific case and it does appear to be technically feasible (although there are still some questions to be resolved on the practicalities of fibre installation and the construction of the correlator). The e-MERLIN upgrade would secure the future of the Facility for at least 10 years. Without this advance it is clear that the subject of centimetre-wave astronomy will largely wither away in the UK.

To be viable e-MERLIN needs to be started quite soon, if possible within the next 1 or 2 years. The Panel feels that given the limited finance likely to be available, and perhaps even more crucially, the limited skilled manpower, the project should concentrate on core issues. The highest priority should be sensitivity and resolution in the range 1.4 to 18 GHz. Careful choices must be made on the number of frequency bands to be covered. Continuous frequency coverage is not essential and the Panel considered that, although there were important observations to be made at K-band (frequencies around 22GHz), the installation of receivers for this band should take lower priority. Questions such as whether it is worth installing multi-beam receivers on the Lovell dish will also need to be looked at carefully. Items that are at present open to considerable uncertainty are: a new style of optic fibres buried in existing roads (MCS - Micro Cable System), which is not yet licensed in the UK; and the proposed WIDAR correlator, which is to be built by the Canadian group in Penticton. In the case of the latter project, the concern is due to the fact that the dominant project for this Canadian group is expected to be a much larger WIDAR correlator which they propose to build for NRAO as a part of the e-VLA Phase I project. The Panel also noted that the resources identified for managing the e-MERLIN upgrade seemed small given the complexity of the project.

If the money for replacing the Defford antenna cannot be found, it would still be worth proceeding with the other aspects of the e-MERLIN project (i.e. the broad-banding). This would however severely affect the performance of the array at frequencies above 5 GHz. A possible partial solution to this problem - replacing the surface with panels with those from the old Dwingeloo telescope - is being considered. Although it would be relatively cheap, the Panel had doubts as to whether this would really be worthwhile. Certainly the practicalities of such a plan and the real performance to be expected should be checked very carefully before proceeding.

The Panel were told of the possibility that a new 32-metre antenna would be built in Ireland which would be linked to MERLIN. It was recognized that this was an interesting development which would provide increased angular resolution. The obvious concern is that setting up such an antenna and linking it into the correlator and operational base at Jodrell Bank will produce additional burdens on the already hard-pressed core staff. The Panel therefore urged that a very careful assessment should be made of the effort needed to carry out this project, both in construction and in the operations phase. The necessary support for staff, including extra personnel at Jodrell Bank, should be secured before any commitments are made.

In addition to the need for significant investment in equipment for MERLIN, the panel noted that much of the infrastructure that supports the Facility is in need of renewal. Many of the buildings are old and appear to be in a rather poor state. The Panel were given to understand that under present arrangements this responsibility lies with the University rather than the Research Council.

Very Long Baseline Interferometry:

The National Facility plays a major role within the EVN (European VLBI Network). The University of Manchester was one of the founding members in 1980. An example of the close, effective collaboration between the NF and the EVN is the major contribution made by NF and JBO personnel in the design of the hardware and the implementation of the software for the new EVN correlator at JIVE (Joint Institute for VLBI in Europe) in the Netherlands. This valuable experience will assist the NF staff in carrying out future upgrades to the MERLIN system, including e-MERLIN. Although the MERLIN/VLBI National Facility expends only about 10 per cent of its budget and has ~3 full-time-equivalent personnel for VLBI activity, the scientific impact of the NF group on European VLBI is quite prominent. The EVN has unique capabilities and provides coverage of certain frequency bands not available on other VLBI facilities. A number of NF and JBO staff play important roles within the EVN - several are well-known VLBI astronomers who have obtained some of the key recent results with the technique. There is, however, some concern that only a handful of UK institutes are now active the VLBI field, although it is hoped that JIVE will help to bring in new users.

The current JIVE subscription from the UK is 85k pounds, which is paid though the National Facility and is in addition to the 10% figure quoted above. A recent European Science Foundation report (chaired by Prof Fenstad) has given an overview of the scientific impact, history, current status and plans for the future of the EVN and JIVE. The report discusses a new method for obtaining more predictable means of support for JIVE, perhaps involving more funding direct from EU sources. If this is not successful it is likely that increased support will be sought from the present partners.

The panel recognizes the success and potential for European VLBI activities and for UK participation. The Panel feels that the present level of effort and financial support for VLBI is probably at the upper end of what can be justified given the tight funding situation of the National Facility. If an increase in the UK funding for JIVE is required in the future, it is essential that this should not be taken from the MERLIN operating budget.


MERLIN National Radio Astronomy Facility Review Committee
Terms of Reference

The PPARC wishes to set up a Review Committee to review MERLIN and associated UK support for VLBI in order to provide an international and independent perspective on its operation and its scientific productivity. The Review Committee will make recommendations to the MERLIN Steering Committee and through it to the Director Science PPARC.

The aims of the Review Committee are to:

(i) comment on the international competitiveness of MERLIN with particular reference to scientific output and relevance to the astronomical community of the UK;

(ii) review the current organisation and operation of MERLIN in relation to its operating budget and recommend how the budget might best be targeted to ensure maximum scientific effectiveness;

(iii) consider the future options and requirements for MERLIN in respect to the likely prospects for radio astronomy for the next ten years.

The Review Committee shall comprise a chairman and three (or possibly four) members of international astronomical distinction. Its membership is to be agreed by the MERLIN Steering Committee in consultation with PPARC. PPARC will provide administrative support where requested. Organisation of the Group's work should be planned so as to be able to report by the end of the year 2000.