The European Science Foundation is an association of its 62
member research councils and academies in 21 countries. The ESF brings European scientists together to work on
topics of common concern, to co-ordinate the use of expensive facilities, and to discover and define new endeavors that will benefit from a co-operative approach
On behalf of European radio astronomers, the ESF Committee on Radio Astronomy Frequencies, CRAF, coordinates activities to keep the frequency bands used
by radio astronomers free from interference.
The scientific work sponsored by ESF includes basic research in the natural sciences, the medical and biosciences, the humanities and the social sciences.
The ESF links scholarship and research supported by its members and adds value by cooperation across national frontiers. Through its function as coordinator, and also by holding workshops and conferences and by enabling researchers to visit and study in laboratories throughout Europe, the ESF works for the advancement of European science.
On behalf of European radio astronomers, the ESF Committee on Radio Astronomy Frequencies, CRAF, coordinates activities to keep the frequency bands used
by radio astronomers free from interference.
The final meeting of Task Group 1-3 concluded at the end of October. The results will be of concern to all who are worried by the problems of electromagnetic pollution. The task group has produced a revised recommendation on spurious emission limits which is to be presented to WRC-97 in a year's time. The recommendation contains three tables of emission limits, only the first of which (Category A limits) are destined to appear in the Radio Regulations. These Category A limits represent a lowest common denominator which all countries are prepared to live with. They are generally far more relaxed that the limits which are being set within Europe by ETSI (Category B). In some cases they even represent a step backwards from the current limits. A more detailed discussion will have to wait until the next Newsletter.
What will be of particular concern to radio astronomers is that the space services were not willing to accept even Category A limits except as "design goals" until they have made further studies. Not only this, but they wish the spurious emission limits to be specified in a narrow band (4 kHz). This leads to a further 24 dB relaxation of the limits on broad band spurious emissions from systems like Iridium and ASTRA. The space services did not give technical justification for the privileges that they are claiming over other services. The 4 kHz band is to be used even for earth stations (such as mobile handsets) where it is not clear why space services need special consideration. The ITU works by consensus so if some administrations are prepared to support their space services in this way there is not a lot to be done.
What troubles me most is that the ITU has allocated a large number of satellite bands (space-to-Earth) immediately adjacent to radio astronomy bands. In fact if you count up the MHz then 80% of the bandwidth allocated to radio astronomy on a world-wide primary basis lies adjacent to a space-to-Earth band. Looking through the bands we see many which are familiar problem areas, such as 1610.6-1613.8 MHz. But there are many more problems waiting to come once the satellites are launched and start transmitting. We are right to be worried.
To make matters worse, the satellite community is not satisfied with its current allocations. It is actively seeking much wider bands to support the ambitious systems of the future like Teledesic and M-Star (son of Iridium). Is it right for these allocations to go ahead wholesale while the issues of satellite pollution are under study and while the space services cannot accept limits like other services, but only design goals? Radio astronomers in all countries of the world need to be aware of these issues and publicize them. We need tighter regulations on satellite pollution so that progress can benefit everyone.
CRAF participated in 3 meetings of the CEPT SE28 project team since the 20th CRAF meeting. CRAF input documents were extensively discussed in SE28. However, the pressure by the MSS operators is steadily increasing. Radio astronomers have to fight against the proposition of some operators that for radio astronomers it does not matter when they wait "a little longer" for their data and that when radio astronomers lose data because of interference, observations can be repeated. It appears from the many discussions held so far that Motorola does not want a discussion about technical details, i.e. about what has been or can be implemented in its system to protect the Radio Astronomy Service, but it only wants that radio astronomers accept its dictate.
The protection of mm-wave astronomy is becoming an issue of concern. Vehicular radar may cause significant interference from harmonics of the transmitted signals at frequencies above 200 GHz. Satellite-borne cloud radar systems which are proposed for 95 GHz will have the potential to destroy sensitive SIS receivers. The updated mm-astronomy position document addressed various aspects of frequency protection, re-allocation and needs for different or more frequency bands. CRAF asked IUCAF to review the mm-frequency use, needs and priorities. It became clear that mm-astronomers have to worry already about the frequeny use and protection for frequencies between 275 and 400 GHz.
The progress of TG1/3, which was setup for looking to harmful spurious EMI of active users into passive services, is a matter of great concern. Its initiative, to report at the WRC97 on spurious emission questions raised at the WARC92, has in fact been taken over by the operators and the agenda had been adjusted to their will. Much effort is needed to bring the task group back on its initial track.
Among the other topics discussed were the severe interference problems in Italy at 1.6 GHz (which prevent Italy to be a reliable and full participant in the VLBI operations at this frequency); interference from an unregistered satellite system at 328.25 MHz, continuing trouble at 10.6-10.7 GHz because of the ASTRA transmissions and a new channel 38 TV transmitter in Denmark. CRAF is working hard on the solution of these problems.
The ITU showed interest in the CRAF EMI-database which resides at Nanšay. Up to date interference reports from European radio observatories are urgently needed.
CRAF is also investigating the possibilities to become an ITU Sector member. This is important since various interest groups of active frequeny users have this status already. Radio astronomy should participate as soon as possible at the Sector member level in ITU activities.
From 28 August - 5 September, 1996, the 25th General Assembly of the URSI was held in Lille, France. Most of the CRAF members partcipated in this conference. Ample attention was paid to the problems of ether-pollution, harmful interference, problems of interference in radio astronomy. Also various aspects of spectrum management and utilization (in general) received attention.
CRAF's contributions were:
R. J. Cohen described the beauty and vulnerability of research of the OH radical in the 1.6 GHz domain. He referred to the improvements for radio astronomy in the frequency bands in this domain for which the it has a primary allocation, due to the cooperation with the GLONASS administration: GLONASS satellites moved out of these frequency bands. He also explained why the Iridium system which will operate both up- and downlink in the 1.6 GHz domain, will have a severe impact on radio astronomical research at 1.6 GHz.
H. C. Kahlmann (former CRAF chairman) described the work of CRAF and its current position in Europe. CRAF being an associated committee of the European Science Foundation has good cooperations with various administrations, the CEPT, the European Commission (although both organizations have deviating interests). CRAF serves IUCAF and CORF with information from the regional European scene which may look different from that in other parts of the world, e.g. due to its political fragmentation.
T.A.Th.Spoelstra addressed the question 'Will "Passive Services" and Scientific Applications of Radio Survive?' - the answer is "yes", when  there are a series of "passive-exclusive" frequency allocations to passive spectrum use;  when active users recognized that when they are not able to solve their problems in 98% of the spectrum, they cannot do this in 100% of the spectrum; and  regulatory issues should not be articulated and put in rules and agreements by special interest groups of active spectrum users, but by the "neutral effort" of the administrations of sovereign countries working for the long term best interests of all spectrum users.
A.Winnberg described the specific situation of mm-astronomy. Untill now mm-astronomy hardly suffered from interference, but at present various system are entering within the horizon which carry a potential disaster to radio astronomy: vehicular radar, satellite-borne cloud radar, etc. His plea was: let us not make the same mistakes at mm-wave atmospheric windows as we did for lower frequency radio astronomy: mm-astronomy is best served when the frequencies within atmospheric windows are exclusively allocated to passive spectrum use. Remote sensing people and radio astronomers should cooperate more closely to achieve adequate allocations at frequencies above 275 GHz.
In addition, IUCAF had 2 meetings during this conference (for a report see IUCAF). Items discussed during these meetings included developments of applications operating at mm-wave frequencies, the threat from Iridium (Motorola canceled a meeting between IUCAF and Motorola which had been scheduled to precede the URSI General Assembly).
This URSI General Assembly turned out to be a good opportunity for radio astronomers working on the protection of radio astronomy frequencies to have thorough discussions.
The major part of the discussions were focussed on the protection of radio astronomy. SE28 agreed on the methodology to be adopted for the protection of radio astronomy against unwanted emissions from mobile earth stations, MES. The meeting discussed the document on the methodology of calculation to provide separation distances by default between a radio astronomy site and MES (which implies that outside that area around a radio astronomy observatory no restriction applies to the operation of mobile earth stations, MES). The document has been prepared by CNET. The methodology is based a Monte Carlo simulation. This is based on the principle of sampling random variables from the defined probability distribution of traffic, frequency channel occupancy and number of calls. An executable version of the software is expected to be available soon at France Telecom.
Two examples were calculated: for TDMA and CDMA. However, due to lacking quantitative information from one MSS operator (Motorola) not more than rough examples could be presented.
In addition the meeting concluded that the protection of radio astronomy should be provided by setting site by site separation areas around each radio astronomy observatory depending on the channels used by the MES. Such calculations should be undertaken in collaboration by MSS operators and radio astronomers.
SE28 also concluded that around each radio astronomy observatory measurements should be undertaken to determine the MES effects on radio astronomy observations. This should be done in collaboration between MSS operators and radio astronomers.
The meeting prepared a draft ERC report on the sharing between MES/MSS and radio astronomy. Also draft recommendations to ITU WP7D and ITU WP8D were prepared. These documents explain the method of calculation as mentioned above. The chairman agreed to circulate the draft as soon as approved at the SE WG meeting in early October so that radio astronomers can see it before the WG7 meeting in Geneva.
No progress has been made on the item of unwanted emissions from satellites into radio astronomy observations. This is due to the fact that again Motorola did not provide the promised input information for this study. Motorola said that a new and more realistic solution may be proposed at the next SE28 meeting.
SE28 also discussed the compatibility between TDMA and CDMA systems in adjacent bands and the sharing between several TDMA and/or CDMA systems. For the former, it appears that the spurious emissions of the TDMA satellite downlink will cause interference to the CDMA ground receivers and that further studies are necessary. For the latter, sharing between CDMA systems should be possible while sharing between TDMA and CDMA is not feasible. But sharing between 2 CDMA systems should be possible.
Also unwanted emissions from MES/MSS satellites systems into Fixed Service, GSO MSS and GLONASS were discussed to some extent. Some refinements of the calculations are still needed. This is partly due to lacking information about the different systems involved.
SE28 will meet again on 5-6 December 1996 in Paris and 20-21 January 1997 in Dwingeloo.
Until now mm-wave radio astronomy did not suffer much from harmful interference. But, because of various technological developments one cannot expect that this situation will last much longer: There are currently several proposals for "unlicenced" equipment to be permitted in the USA, such as collision avoidance vehicular radar. There are plans for a satellite-borne cloud radar operating at 94 GHz and several proposed satellite projects will use frequencies around 60 GHz for intersatellite communications. The spectrum occupancy at frequencies above ~ 50GHz is such that at present there are also several allocations in the mm bands for space-to-Earth satellite transmissions which are not used yet (Broadcasting, Amateur, and Radio Navigation services). But nobody should expect that this will remain the case. All the mentioned future applications have the potential to severely limit the access of radio astronomy to the millimetre spectrum. This has significant impact on the progress of astronomical research, since many spectral lines from many molecules are detected at mm-wavelengths. Observations of these spectral lines are of fundamental importance to our knowledge of physical and chemical processes in the Universe. Understanding this, it is recognized that the increasing potential of harmful interference comes at a time when the Radio Astronomy Service actually is in need of increased bandwidth for high sensitivity continuum observations and for studies of line emission from objects at high redshift. Clearly, increased protection for the Radio Astronomy Service is necessary if these astronomical investigations are to go ahead.
CRAF is working on criteria and methods to establish this protection. It is recognized that perhaps the methodology to protect mm-wave astronomy might differ from "common" radio astronomy at lower frequencies, but much has to be studied in more detail. CRAF is eager to receive any comments and recommendations helpful for this study.
Some comments, constraints and criteria can already been given:
It has been proposed several times that some entire atmospheric mm windows should be reserved exclusively for RA - in a manner analogous to Natural Parks or the Antarctic Continent.
A radical step, which has also been advocated, is to allocate whole atmospheric windows to radio astronomy. The justification for this is based on recent discoveries which have led to a new awareness of the potential of the millimetre waveband for astronomy, and has precipitated the planning of several large instruments (see below). For example, it is now known that galaxies and quasars can be detected at high redshifts so that their line emission from carbon monoxide (CO), the most easily detected molecule, can appear in any part of the atmospheric windows, depending on the exact redshift. It seems increasingly likely that studies of these objects will be relatively easy at millimetre wavelengths. One reason is just the higher intrinsic sensitivity attainable at millimetre wavelengths. This is because the thermal emission from these objects displays a spectrum which rises rapidly with increasing frequency. Furthermore, a larger observing bandwidth can be used which for line observations leads to a further increase in sensitivity proportional to the square root of frequency.
In addition, the continuum emission from dust in these objects and others in our own Galaxy can be detected by wide-band bolometer detectors which for the highest sensitivity must utilise a large fraction of a whole atmospheric window (typically 50 GHz).
Yet another important field of study which calls for broadband continuum observations in the millimetre bands is that of the cosmic background radiation. This has its (very broad) peak near 2 mm wavelength. The Sunyayev-Zeldovich effect shows a pronounced absorption at about 2 mm.
Also the density of spectral lines in the mm bands is very high. For example, the frequency range 218 - 263 GHz has been surveyed in the star forming region Sgr B2 N and about 1800 spectral lines from more than 50 different species have been detected, implying a mean density of about 40 lines per GHz. Each such line is potentially a source of astronomical information.
Future large instruments will be designed to explore distant galaxies in more detail with enhanced sensitivity and angular resolution. For example, to study the epoch of galaxy formation at redshifts of 3 or greater, the CO (1-0) line has moved out of the mm windows and the higher order transitions emitted at higher frequency must be used (at rest frequencies of 230, 345, 460 GHz etc). In principle just to study CO in this way requires an octave in frequency so that as one transition moves out of the band at the lower frequency end, the next higher transition enters the top end of the band. The present allocation in the 3mm window only covers the z range out to about 0.1 - and does not take these considerations into account.
The blanket protection of a whole window may still be relatively easy for the 0.8 mm window and shorter, but protections for the more important 1, 2, and 3 mm windows will probably have to be "partial" (i.e. in terms of frequency band allocation) to respect the requirements of other services. Even this limited goal requires large changes in the existing allocations. However, this may still be feasible as the Radio Astronomy Service is the only service which routinely is using these bands at present. Facing the threats appearing within the mm-astronomy horizon, one has to ask severel questions: Which windows are most important? Would it be sufficient to ban satellite transmissions in selected windows, and rely on "quiet zones" for protection from Earth-based emissions? If so, what about aircraft emissions etc? Is it possible to use parts of several windows instead of a whole window for high redshift observations?
At the same time we should keep in mind that far-advanced plans for satellite observatories for the sub-mm range exist. The most imminent satellites of this type are the American SWAS and the Swedish ODIN. They will observe spectral lines of oxygen and water, i.e. the very same species that divide the mm band into a number of windows seen from the ground. ODIN will be equipped also with a receiver for the 119-GHz oxygen line. Therefore protection is needed for at least the 119-GHz line. The atmospheric absorption around 60 GHz is also due to oxygen but it is a complicated band consisting of many densily packed lines. However, due to this the band can be used for determining the temperature profile in the troposphere and the meteorologists are fighting for access to this band.
CRAF investigates several changes with respect to the present situation. These have regulatory and technological aspects. CRAF's aim is a minimum but necessary change to the existing situation to guarantee access to the nearby and distant Universe for studies of carbon monoxide and dust emissions. On the other hand CRAF recognizes the need of well-balanced articulation of possible changes: just as radio astronomers do not want to be harmed by active spectrum users, CRAF does not accept unjustice to these other spectrum users. Therefore, CRAF stimulates where possible efforts to develop new hardware and software tools for proper frequency protection and spectrum engineering. Technological development may open different new and so far unknown possibilities to protect radio astronomy. CRAF's efforts are extended to frequencies up to 1 THz. It does this work in close collaboration with IUCAF. By this it attempts to enable new facilities to work through open windos towards the Universe. At present, the following major new millimetre-waveband observing facilities have been planned:
1) The Millimeter Array of the US National Radio Astronomy Observatory (MMA). 40x8m diameter antennas for 30-366 GHz range.
2) The Large Millimetre and Submillimetre Array of the National Astronomical Observatory of Japan (LMSA). 50x10m diameter antennas for 35-500 GHz range.
3) The Submillimeter Array of the Smithsonian Institution (SMA). 6x6m diameter antennas for 150-890 GHz range.
4) The European Large Millimetre Array (LSA). 50x16m diameter antennas for 80-360 GHz range.
5) The US-Mexican 50m Telescope. Radome enclosed for frequencies up to 230 GHz.
6) The Spanish 40m Telescope. Free standing for frequencies up to 120 GHz.
Interference from a satellite system operating at 328.2 MHz is causing harmful interference to observations in many countries, e.g. as observed in Westerbork (The Netherlands) and India. A joint effort of the Dutch and German administrations in collaboration with the satellite monitoring station in Leeheim (Germany) led to the conclusion that at this frequency radio astronomy is suffering from an unregistered satellite system.
Summary of the characteristics of the interferer is given in the following tables.
|Bandwidth||~ 38 kHz|
|Maximum pfd||-126 dBW/m*m|
|Type of transmission||data bursts|