The Need for a United Asia-Pacific Radio Astronomy Front
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Radio signals from the Cosmos can be incredibly faint – typical spectral power flux densities as low as –320 dB(W m-2 Hz-1) are being detected, and even fainter signals are being sought. Because of this the signals are potentially very susceptible to interference from transmitting services. There are increasing demands for radio spectrum by new or evolving transmitting services, with increasing threat to radio astronomy unless the spectral bands used for radio astronomical observations can be protected.
The usage of the radio spectrum is regulated on an international scale by the International Telecommunication Union (ITU), a specialized agency of the United Nations Organization, by means of the International Radio Regulations. These Regulations are revised at a World Radiocommunication Conference (WRC) held about every three years. Improved protection for radio astronomy can be obtained only at these meetings, and it is extremely important that worldwide representation of radio astronomers with united proposals is present. Administrations have already found that the formation of regional groups such as CEPT, CITEL etc in which common proposals have been established in advance of WRCs, has been very effective in protecting regional interests. In our region administrations have formed the Asia-Pacific Telecommunity (APT) and it played a major role at WRC-2000. For radio astronomy, regional groups have been set up in America (CORF) and Europe (CRAF), and these promoting radio astronomy views in CITEL and CEPT respectively. To enable effective negotiation of protection for radio astronomy within the APT, a similar group representing Asia-Pacific radio astronomers is needed.
Radio astronomy and the radio astronomy service as a radiocommunication service are defined in Article 1, Nos. 14, 55 and 92 of the Radio Regulations of ITU as being astronomy based upon the reception of cosmic radiowaves. The aggregate of these cosmic emissions constitute the cosmic background noise of communications engineering. Being a passive service, radio astronomy does not involve the transmission of radio waves in its allocated bands, and therefore the use of these bands cannot cause interference to any other service. On the other hand, the cosmic signals received are extremely weak (typical spectral power flux densities as low as –320 dB(W m-2 Hz-1) are routinely observed), and are therefore very susceptible to interference by transmissions of other services. At present, radio astronomy utilizes the electromagnetic spectrum at frequencies from below 1 MHz to about 1,000 GHz, well beyond the 275 GHz currently allocated in the Radio Regulations. The entire radio spectrum is of scientific interest to the radio astronomy service.
Radio astronomy began in 1932 when Karl Jansky discovered the existence of radiowaves of extra-terrestrial origin and it is now established as an important branch of observational astronomy. For the solar system, it has increased our knowledge of the Sun, e.g. the physical processes responsible for the emissions of plasmas, and also of the planets and the interplanetary space. On a larger scale, multi-frequency studies of cosmic sources of radio emission have provided information about interstellar gas clouds and star formation within them, interstellar magnetic fields, the structure and the evolution of galaxies, and the Universe as a whole. Spectral-line emissions of atoms and molecules at naturally occurring frequencies have provided information about the composition, the physical characteristics, and the motions of interstellar gas clouds. Much of the information obtained by radio astronomy is unique and cannot be obtained at other than radio wavelengths.
In contributing to our knowledge of astronomy, the radio astronomy service has also contributed to other areas. It has provided information on the atmospheric absorption of radio waves, which is of interest to telecommunications. It has also contributed to communication technology. Its pioneering operations have led to continuing development of low-noise amplifier techniques, extending to progressively higher frequencies and wider bandwidths, and the production of receiver systems with ever increasing sensitivity. In some cases sensitivities approach the theoretical limits. In practice, system temperatures lower than 20 K have been reached. Significant contributions have been made to the design of feed systems and large steerable antennas. The technique of very-long-baseline interferometry (VLBI) is also important for geodetic measurements and for the accurate tracking of spacecraft. The development of very large-scale integration (VLSI) chips to process the data collected by radio astronomy arrays has applications in other areas of electronics and physics. The sophisticated image processing techniques developed by radio astronomers have a direct application in areas such as medicine and mining.
In the study of cosmic radio sources, radio astronomers measure all the properties of electromagnetic radiation. These are: intensity, frequency, polarization, direction (the position in the sky), and temporal variations of these parameters. Cosmic radio emissions have low power flux-density levels at the Earth. Most show the characteristics of random noise. Exceptions are (a) the pulsed emissions at extremely regular rates from pulsars, (b) interplanetary and ionospheric scintillations of small diameter radio sources, (c) irregular bursts from some stars (including the Sun), (d) variations on the scale of months for some radio sources, and (e) variations associated with the planet Jupiter. The best times for observation of radio sources are generally dictated by natural phenomena (the position of the source in the sky and the rotation of the Earth). Unlike the situation in active (transmitting) services, the radio astronomer cannot change the character of the signal to be received; the emitted power cannot be increased, or the signal coded, in order to increase detectability.
The radiation measured in radio astronomy has, in almost all cases, a Gaussian probability distribution in amplitude. Generally it cannot be distinguished from thermal noise radiation of the Earth or its atmosphere, or from noise generated in a receiver. In radio astronomy observations the signal-to-noise ratio in the radio frequency (RF) and intermediate frequency (IF) parts of the receiver is typically in the range -20 dB to -60 dB, i.e. the power contributed by the source under study is a factor of 10-2 to 10-6 lower than the unwanted noise power from the atmosphere, the ground, and the receiver circuits. In most communication systems the corresponding signal-to-noise ratio is of the order of unity or greater. Because radio astronomy signals are so weak in comparison to those of other services, radio astronomy observations are highly vulnerable to radio interference, and to exacerbate the problem cosmic signals generally have no characteristic modulation that would help to distinguish them from noise or from many forms of interfering signals.
The reason that observations with very low signal-to-noise ratio can give useful measurements is that when the total noise power in the receiver IF stages is measured using a detector, and the output of the detector is averaged for many seconds, or in some cases many hours, the statistical fluctuations in the measured values are greatly reduced. It is commonly possible to detect fractional changes in the total noise level that are of the order of 10-6 or lower. An example of the high sensitivity of radio astronomy observations is the detection of the angular structure in the cosmic background radiation by the Cosmic Background Explorer (COBE) satellite in 1992. Fluctuations of the order of 10-5 of the 2.7 K background temperature were measured, which are 70 dB below the system noise temperature of 200-400 K of the receivers on the satellite. The high sensitivity of such observations is obtained at the expense of information on short-time variations of any signal characteristics, which are lost in the averaging that is essential in reducing the noise fluctuations.
3. International and Regional Organizations to treat Frequency Allocation Problems
This document is concerned principally with aspects of radio astronomy that are relevant to frequency coordination, that is, the usage of the radio spectrum in a manner regulated to avoid interference by mutual agreement between the radio services. On an international scale, the regulation of spectrum usage is organized through the International Telecommunication Union (ITU), which is a specialized agency of the United Nations Organization.
The Radiocommunication Sector which is a part of the ITU was created on 1 March 1993 to implement the new ITU structure. The Radiocommunication Sector includes World and Regional Radiocommunication Conferences, Radiocommunication Assemblies, the Radio Regulations Board, Radiocommunication Study Groups, the Radiocommunication Advisory Group and the Radiocommunication Bureau headed by the elected Director. The Radiocommunication Assembly and the Radiocommunication Bureau replaced the International Consultative Committee on Radio (CCIR) and its Secretariat which performed similar functions.
The ITU Radio Regulations, which are the basis of the planned usage of the spectrum, are the result of World Radio Conferences (WRCs), which are held at intervals of a few years. At such conferences, the aim is to introduce new requirements for spectrum usage in a form which is, as far as possible, mutually acceptable to the representatives of participating countries. The results of each WRC take the form of a treaty to which the participating administrations are signatories. As in most areas of international law, the enforcement of the regulations is difficult, and depends largely upon the goodwill of the participants.
Radiocommunication Study Groups are set up by a Radiocommunication Assembly. They study questions and prepare draft recommendations on the technical, operational and regulatory/procedural aspects of radiocommunications. These ITU-R Study Groups address such issues as preferred frequency bands for the various services, threshold levels of unacceptable interference, sharing between services, desired limits on emissions, etc. These groups are further organised into Working Parties and Task Groups which deal with specific aspects of Study Group work. As of 2001 the ITU-R Study Groups are as follows:
Study Group 1 Spectrum management
Study Group 3 Radio wave propagation
Study Group 4 Fixed-satellite service
Study Group 6 Broadcasting service (terrestrial and satellite)
Study Group 7 Science services
Study Group 8 Mobile, radiodetermination, amateur and related
Study Group 9 Fixed service
SC Special Committee on Regulatory / Procedural Matters
CCV Coordination Committee for Vocabulary
CPM Conference Preparatory Meeting
Radio astronomy falls within ITU-R Study Group 7, Science Services, which also includes space sciences, time signals and frequency standards. In the work of the Study Group, the search for extraterrestrial intelligence (SETI), radar astronomy as practiced from the surface of the Earth, and space-based radio astronomy are usually included with radio astronomy.
International meetings of the Study Groups and Working Parties occur at approximately two-year intervals, and are attended by delegations from many countries. The Task Groups are usually set up for a limited period of time to carry out specific tasks, and meet at intervals according to their needs. Appropriate Questions are assigned to the Study Groups, which provide responses generally in the form of ITU-R Recommendations. The ITU-R Recommendations provide a body of technical, operational and regulatory/procedural information that has been agreed upon by the participating administrations. This information is used to provide technical inputs to WRCs, and many of the results of the work of the Study Groups are thereby incorporated into the Radio Regulations. Aside from this, the ITU-R Recommendations and Reports are, in themselves, generally regarded as authoritative guidelines for spectrum users. This is particularly true of the ITU-R Recommendations, which are widely followed, and are revised and published on a four-year cycle by the ITU. Since 1990, the Reports are no longer carried forward in current ITU publications. Most of the important material on radio astronomy in Study Group 7 Reports has been revised.
International frequency allocations are carried out at WRCs, attended by representatives of more than 180 administrations from all over the world. For the purpose of allocation, the world is divided into three regions: Region 1 includes Europe, Africa and northern Asia; Region 2 includes North America and South America; Region 3 includes southern Asia and Australasia. For any particular frequency band, the allocations may be different in different regions. Bands are often shared between two or more services. Generally speaking, the allocations are primary or secondary. A service with a secondary allocation is not permitted to cause interference to a service with a primary allocation in the same band. The frequency allocations are contained in Article 8 of the Radio Regulations. Most are shown in a table of allocations; however, additional allocations are contained in numbered footnotes to the table.
Within individual countries, spectral allocation matters are handled by government agencies. The agencies vary greatly from one administration to another. In many countries, the administration of the radio spectrum is part of the work of a larger agency which may also include areas such as postal and telephone services, transportation, commerce, etc. Such agencies play major roles in the preparation of national positions that are advocated at WRCs. Administrations participating in the WRC treaties retain sovereign rights over the spectrum within their national boundaries, and can deviate from the international regulations to the extent that this does not cause harmful interference within the territories of other administrations. In the setting up of the Radio Regulations, many administrations have claimed exceptions in certain bands in order to cover particular national requirements.
Several features of radio astronomy are different from those of the majority of services that use the radio spectrum. Radio astronomy is a passive service, concerned only with the reception of data. A few other services, such as Earth exploration by satellite, also use passive sensing.
Radio astronomy signals are very weak, with power flux densities typically 40 to 100 dB below those utilized by most other services. The highly sensitive receiving systems that are required in radio astronomy are very vulnerable to interference. This vulnerability is exacerbated by the nature of the cosmic signals. Most signals have the form of random noise, with no characteristic modulation that would allow them to be distinguished from other signals. The sharing of frequency bands with active services is difficult. It is usually not possible to share when there is a direct line-of-sight between a radio astronomy antenna and a transmitter in the same band. A further problem is emission produced in a radio astronomy band by active services operating in other bands. This is becoming more common as the use of broadband digital-modulation and spread-spectrum techniques continues to increase. Because of this potential threat to radio astronomy, mere preservation of allocations is not sufficient to guarantee interference-free radio astronomical observations.
Radio astronomers cannot always choose their frequencies arbitrarily. Many of the cosmic signals that they study take the form of spectral lines covering a limited frequency range. These lines are generated at characteristic frequencies associated with transitions between quantised energy states of atoms or molecules. Thus, allocations for observation of these lines must be made at specific frequencies. Allocations for many of the more important lines were obtained in the past, when the radio spectrum was less heavily used by other services. Additional allocations will be required, but will be difficult to obtain. Important new lines continue to be detected, and many of them are not within allocated bands. For spectral lines in distant galaxies, an observed frequency that normally falls within a radio astronomy band may be Doppler shifted outside the band because of the large motions of the galaxies relative to the Earth. Therefore, practically all parts of the radio spectrum are of potential scientific interest. However, because of allocations to active services, observations at many frequencies are severely restricted, or not even possible. In some cases, it may be possible to minimize interference by choosing appropriate locations for telescopes, or times for observation.
Because radio astronomers have great difficulty in sharing frequencies with active services, and cannot choose their frequencies arbitrarily, radio astronomy is not easily accommodated within the system of allocations and regulations. Nevertheless, the series of bands allocated to radio astronomy is vital to the existence of the service, and has enabled a stream of important scientific discoveries to be made over the past three decades.
Radio astronomy was first officially recognized as a radiocommunication service at the WARC of 1959. At that time, under the auspices of the International Council of Scientific Unions (ICSU), three scientific unions set up a commission, the Inter-Union Commission for the Allocation of Frequencies for Radio Astronomy and Space Science (IUCAF) to represent scientific usage of the radio spectrum. The three founding unions are the International Astronomical Union (IAU), the International Union of Radio Science (URSI), and the Committee on Space Research (COSPAR); each contributes to the membership of IUCAF. IUCAF participates in WRCs as a recognized International Organization, but has no voting rights. Radio astronomers work through their national agencies or IUCAF to get their concerns considered by the Radiocommunication Sector, or included on the agenda of a WRC. In addition to IUCAF, National and Regional committees, for example the US Committee on Radio Frequencies (CORF) and the European Committee on Radio Astronomy Frequencies (CRAF), facilitate a united participation by radio astronomers. Figure 1 illustrates some of the inter-relationships between agencies involved in frequency coordination processes for radio astronomy.
Inter-relationships between international agencies involved in frequency coordination for the radio astronomy service
where (in alphabetical order):
CORF Committee on Radio Frequencies
COSPAR Committee on Space Research
CRAF Committee on Radio Astronomical Frequencies
IAU International Astronomical Union
ICSU International Council of Scientific Unions
ITU International Telecommunication Union
IUCAF Inter-Union Commission for the Allocation of Frequencies for
Radio Astronomy and Space Science
RA Radiocommunication Assembly
SG 7 Study Group7
URSI International Union of Radio Science
WRC World Radiocommunication Conference
In Article 1, Section 1 of the Radio Regulations, radio astronomy is defined as astronomy based on the reception of radio waves of cosmic origin. In the table of frequency allocations, frequency bands which offer the greatest protection to radio astronomy are those for which the radio astronomy service has a primary allocation shared only with other passive (non-transmitting) services. Next in degree of protection are the bands for which radio astronomy has a primary allocation but shares this status with one or more active (transmitting) services. Less protection is afforded where bands are allocated to radio astronomy on a secondary basis.
For many frequency bands, the protection is by footnote rather than by direct table listing. The footnotes are of several types. For an exclusive band allocated only to passive services, the footnote points out that all emissions are prohibited in the band. Other footnotes are used when radio astronomy has an allocation in only part of the band appearing in the table. A different form of footnote is used for bands or parts of bands which are not allocated to radio astronomy, but which are nevertheless used for astrophysically important observations. It urges administrations to take all practicable steps to protect radio astronomy when making frequency assignments to other services. Although such footnotes provide no legal protection, they have often proven valuable to radio astronomy when coordination with other services is required.
4. The Success of CRAF and CORF
Administrations have already found that the formation of regional groups such as CEPT, CITEL etc in which common proposals have been established in advance of WRCs, has been very effective in protecting regional interests. For radio astronomy, regional groups have been set up in America (CORF) and Europe (CRAF), and these promoting radio astronomy views in CITEL and CEPT respectively.
CRAF has regular meetings at least twice a year, and contributed to submit European common views and proposals for relevant Study Group meetings and WRCs. An excellent example would be the success of extending frequency allocations for radio astronomy above 71 GHz that was made in WRC-2000. Radio astronomy could not extend its frequency allocations after 1979. Therefore radio astronomers of CRAF, CORF and some astronomers from Asia-Pacific region collaborated to negotiate with other services within their regions, and succeeded to submit very similar proposals for WRC-2000. Thus discussion among participating administrations during WRC-2000 ran very smoothly, and radio astronomy could get new frequency allocations of more than 80 GHz in total in the frequency region between 71 and 275 GHz. CRAF and CORF prepared radio astronomers proposals to CEPT and CITEL, respectively, and played major role to adopt them as the regional common proposals. Submission of such common proposals are quite effective for radio astronomers to realize what we need, when we take the decision-making procedures within ITU into account.
Although the frequency problems are regulated under national laws, radio waves propagate regardless with the national borders. Therefore it is quite necessary to have common views between neighboring countries on any frequency allocation / regulation issues. The role of CRAF and CORF will be heavier and heavier in the future.
5. The Need to establish a Radio Astronomy Frequency Committee in the Asia-Pacific region (RAFCAP)
In Asia-Pacific region, administrations have formed the Asia-Pacific Telecommunity (APT) and it played a major role at WRC-2000. However there has not been any regional radio astronomers group to collaborate the frequency allocation problems. The APT’s regional meeting for preparation of WRCs are called APGs. As was seen in Europe and in America, it would be quite effective for radio astronomers group to participate the APG meetings to solve the frequency allocation problems on radio astronomy. So far only small number of active radio astronomers from Australia, India, Japan and the Republic of Korea worked as their national delegates. When we refer to the success of CRAF and CORF, it is clear that we need a more coordinated radio astronomy group to effectively reflect our opinions to the APG common proposals.
In our region several countries have radio astronomical facilities: Australia, China (Peoples Republic of), India, Japan, Korea (Republic of). Although Taiwan has no radio astronomical facilities at present, radio astronomers in Taiwan have been participating to the SMA project. In 1999 it was discussed to establish a group to collaborate on the frequency issues in the 4th East Asia Meeting of Astronomy held in Kunming, Yunnang, China. The participants agreed to support the establishment of such group.
The Asia-Pacific countries show very different situations in their infrastructures on radiocommunication. For developing countries it is an economical decision to introduce mobile phones rather than wired phones in establishing communication networks. Therefore radio observational environment would be polluted more and more unless radio astronomers act to protect themselves.
6. Establishment of the RAFCAP
During the last AP-RASC meeting, held from 31 July to 4 August, 2001, in Tokyo, there was a business meeting (August 3rd) to discuss the need to establish the radio astronomers group to handle the frequency issues in the Asia-Pacific region. I made a presentation to explain the need to set up the group. Dr. Ananthakrishnan (India), Dr. Chung (Korea, Republic of) and Dr. Tzioumis (Australia) reported national activities to protect radio astronomy in each country. After discussion among participants to the meeting, the RAFCAP (Radio Astronomy Frequency Committee in the Asia-Pacific region) has been launched successfully !
The initial members of the RAFCAP are as follows:
Chairperson -- Masatoshi Ohishi (NAO, Japan)
Secretary -- Tasso Tzioumis (ATNF, Australia)
Makoto Inoue (NRO, NAO, Japan)
S. Ananthakrishnan and T.L. Venkatasubramani (GMRT, TIFR, India)
Uday Shankar (RRI, India)
X. Hong (Shanghai Obs. China)
S. Wu (National Astr. Obs., China)
H.S. Chung (Korea Astr. Obs., South Korea)
The RAFCAP (Radio Astronomy Frequency Committee in the Asia-Pacific region) has been successfully established, and the appendix provides a proposed draft charter of the committee, which was made by referring to that of CRAF. (Square bracketed parts are tentative – like the ITU manner.) Although we need financial supporters in near future, it is necessary to actually work as soon as possible and show how our committee is so effective in protecting radio astronomy in the Asia-Pacific region. It is planned to have the first plenary meeting during the 3rd APG meeting which is scheduled to be held in March 2002 in Tokyo.
Proposed Draft Charter of the Radio Astronomy Frequency Committee in the Asia-Pacific region (RAFCAP)
1. RAFCAP Status and Mission
RAFCAP acts as the scientific expert committee on frequency issues for the Asia-Pacific radio astronomy and related sciences.
The mission of RAFCAP is
(a) to keep the frequency bands used for radio astronomical observations free from interference.
(b) to argue the scientific needs of radio astronomy for continued access to and availability of the radio spectrum for radio astronomy within the Asia-Pacific region.
(c) to support related science communities in their needs of interference-free radio frequency bands for passive use.
2. RAFCAP Terms of Reference
- provide scientific advice for the co-ordination of a common Asia-Pacific policy on frequency protection for radio astronomy, and related sciences;
- promote understanding on the issue of passive frequency use for scientific observations;
- provide a discussion forum on interference issues in passive frequency use, and increase public awareness of these fields at the Asia-Pacific level and the international level.
In the pursuit of these tasks, RAFCAP will interact with the relevant major bodies and supranational entities at the Asia-Pacific and international level.
RAFCAP Committee Members are required to maintain links with their national observatories involved in radio astronomy and with their national radiocommunications administrations.
3. RAFCAP Committee Membership and Structure
Committee Members are drawn from reputed experts active in all fields of radio astronomy and related sciences on the basis of scientific or technical expertise and recognition within the community, so as to ensure the authority and credibility of the Committee. A credible representation of the Asia-Pacific radio astronomy observatories and a geographical balance of the Committee’s membership needs to be ensured.
The Committee Members are appointed for a three-year term, normally renewable, after appropriate consultation with RAFCAP and with the respective national bodies.
The Chairperson of RAFCAP is appointed in response to his/her nomination by the RAFCAP Committee. The search for candidate(s) for its chairperson is undertaken by a Search Panel set up by the Committee. The term of the RAFCAP chair is three years with a possible extension for up to two more years.
The Committee shall be responsible for the appointment of a Secretary [and a Frequency Manager] to support the Committee in its activities, and undertake any other activities the Committee may require.
4. Member Institutions of RAFCAP
Member institutions of RAFCAP – supporting the meetings and the Frequency Manager of the Committee – should be involved in radio astronomy, or related sciences.
New member institutions are accepted after consultation with RAFCAP and the existing institutions.
5. RAFCAP Modus Operandi
The Committee shall normally hold at least one plenary meeting per year at which all business items are considered. The committee meetings are convened by the RAFCAP Chairperson. Additional meetings or teleconferences are convened as appropriate.
The Committee may establish procedures as necessary to meet its mission.
The Committee, if it is deemed necessary, may draw up a set of detailed regulations for its modus operandi, in line with the Charter.
6. RAFCAP Finance
The costs of the Committee’s meetings [and of the RAFCAP Frequency Manager] are financed by the member institutions.
Contributions from other bodies - such as national research agencies and institutes, or other institutions – may also be sought.
RAFCAP finances are regularly audited by one of the RAFCAP member institutions.
7. Reporting and Advising Activities of RAFCAP
The Committee reports, as appropriate, [in particular to the Directors’ Committee in the Asia-Pacific region, and] to the RAFCAP member institutions.