Letters of Intent received in 2022

LoI 2024-2172
The Scientific and Technical Spectrum of Radio Astronomy

Topics

- Frequency coverage and technology of present and future receivers in radio astronomy
- Milestone frequencies in the redshift distribution of HI
- New and future discoveries observing Galactic molecular lines
- New and future discoveries observing extragalactic molecular lines
- The most important phenomena and frequencies in pulsar- and transient research
- Anchor frequencies and present and expected science in radio continuum astrophysics
- Defining priority bands for the upcoming decade(s) in order to facilitate the regulatory processes to protect current and future radio astronomy operations

Editors:
Gyula I. G. Józsa, Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
Michael Lindqvist, Onsala Space Observatory, S-439 92 Onsala, Sweden
Anastasios Tzioumis, CSIRO, P.O. Box 76, Epping, NSW 2121, Australia

Rationale

In the light of the developments in the radiocommunications sector and the technical advances in radio astronomy, it is unavoidable to request increased regulatory protection for our telescopes and hence the additional allocation of radio bands to the Radio Astronomy Services (RAS) at the Radiocommunications Sector of the International Telecommunication Union (ITU-R). This ambitious goal can earliest be addressed at the World Radiocommunication Conference (WRC) in 2027. To start with this process, a review and update of the official ITU lists of the most important radio bands is required. This, in turn, can be realised only with the support of the International Astronomical Union (IAU) as the world's authority on astronomical questions.

We hence propose to review and update the list of important radio frequencies organised by the radio astronomical representations at the ITU-R and the IAU. As a milestone in this process we propose to organise a Focus Meeting at the IAU General Assembly (IAUGA) in 2024 in Cape Town. Results achieved by this time can be summarised, further input can be collected and a strategy towards the World Radiocommunication Conference in 2027 can be developed. The Focus Meeting will also provide a summary of the present and expected milestones in radio astronomy at present and in the near future. At the same time, the formal review of the corresponding ITU documents will be started to finally approach the target to request additional frequency allocations.

A more detailed background:
Emission from transmitters in protected and unprotected radio astronomy frequency bands (by radio astronomers summarised under the term radio frequency interference, RFI) is increasingly affecting radio astronomical observations. One of the reasons for this is the increasing economic pressure to efficiently use the whole spectrum for individual communication or data transfer at lower frequencies (< 75 GHz). On the other side, new technological developments like car radar have created demand even at frequencies well into the mm and sub-mm regime, up to 1 THz, which were hitherto barely used by industry. At the same time, there is the tendency to design radio astronomical receivers to cover an as wide frequency range as possible which makes receivers more susceptible to RFI.

Hence, radio stations require the continuing support by the whole community to protect radio astronomy as best as possible from the impact of transmissions of active radio services.

The protection of radio astronomy bands by the United Nations' International Telecommunications Union Radiocommunications Sector (ITU-R) is realised in the ITU-R Radio Regulations (RR) through allocations of frequency bands to the Radio Astronomy Service (RAS) at different levels of protection. The RR have the status of an international treaty and are binding worldwide. The RRs are updated approximately every 3-4 years at World Radio Conferences (WRCs). The next WRCs will be in 2027 and 2030. Any new frequency allocation will be first suggested by national administrations in a WRC (2027) as an agenda item for the next WRC (2030). This implies that the national agencies, the main actors in the ITU-R, have to be convinced of the suitability of the new allocation well in advance supported by a set of studies. The ITU-R also publishes Reports and Recommendations, which contain supplementary information, such as acceptable levels of interference from services in adjacent bands. On acceptance at the WRC (2030), any new allocation will take effect immediately.

In the RRs, below 75 GHz less than 2 percent of the spectrum is granted a guaranteed ("primary") allocation to RAS, while between 75 GHz and 275 GHz it is 36 percent. This means that most radio astronomical observations are opportunistic: observations are conducted at frequencies not allocated to the RAS in the hope that at the time of the observation they are not heavily corrupted by the services with an allocation in the specific radio band. Through monitoring and defending the few allocated RAS bands the emission in the opportunistic regime is to some extent also controlled as it cannot reach a level where its spill into the RAS bands exceeds the limits laid down in the ITU-R regulation. Complementary protection zones enforced by national authorities may mitigate the RFI situation around observatories.

The ITU maintains two lists of frequency bands, which are of tremendous importance for radio astronomy: allocations of radio bands in the RRs are based on these lists. Recommendation ITU-R RA.314 ("Preferred frequency bands for radio astronomical measurements") addresses frequencies below 1000 GHz and has last been updated in 2003. Recommendation ITU-R RA.1860 ("Preferred frequency bands for radio astronomical measurements in the range 1-3 THz") was last reviewed in 2010. Both documents are assumed to reflect the collected wisdom of the broadest possible basis in the astronomical community, which is why in the past the lists were maintained and supported by the IAU.

The review of both lists is long overdue and is unavoidable if further frequencies should be filed for protection at the ITU. However, to update the list, the collaboration of the worldwide astronomical community, hence the IAU, is required.

An initiative by MPIfR, CRAF, and ORP:
Michael Kramer, Chair of ERC Opticon RadioNet Pilot Joint Action "Preserving the future generations"; Director at MPIfR
Gyula Józsa, Organizer of ERC Opticon RadioNet Pilot Joint Action "Preserving the future generations"; European Committee on Radio Astronomy Frequencies (CRAF); MPIfR
Benjamin Winkel, CRAF Chair; MPIfR
Michael Lindqvist, CRAF; Onsala Space Observatory