The Need for a United Asia-Pacific Radio Astronomy Front
2-21-1, Osawa, Mitaka,
Tokyo, 181-8588 Japan
Tel: +81 422
34 3575; Fax; +81 422 34 3840; e-mail: masatoshi.ohishi@nao.ac.jp
Abstract:
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
satellite
services
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.
Figure
1
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)
7. Conclusion
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.
Appendix
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
RAFCAP will
-
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.