Synopsis
The number of innovative, world class radio telescopes has never been higher. while at the same time new facilities are being planned, built, and upgraded at a breathtaking speed. The building phase of the Square Kilometre Array has started, while in its anticipation numerous telescopes with already unprecedented performance have been constructed. With the Five-hundred-meter Aperture Spherical radio Telescope, the largest single-dish telescope on Earth has been built and the ngVLA is already in the design review phase. The Atacama Large Millimetre Atacama Large Millimeter/submillimeter Array is in operation for a decade, while the NOrthern Extended Millimeter Array has just been inaugurated. The Event Horizon Telescope pushes the limits of angular resolution down to finally confirm the nature of black holes at the centres of galaxies. The first tests on- and around the Moon have been performed, and lunar radio telescopes in the shielded zone of the moon are being planned, unhindered by atmospheric absorption and, hopefully, interference from artificial sources.
The already high scientific relevance of radio astronomy is hence increasing to an unprecedented level. Surveys with ALMA and SKA progenitor instruments give insights into fundamental physics, cosmology, galaxy-, stellar-, and planetary evolution and offer statistical approaches where in the past only single objects were observed. The dark matter structure of galaxies and the cosmic web is being explored, the time and spatial variations of fundamental constants of physics through cosmic time is probed, atmospheres of exoplanets are observed, and long term monitoring of radio spectral line observations might make an expansion of the universe directly detectable.
However, as much as radio astronomy advances, the same is true for the telecommunication sector. More and more radio spectrum is used to transmit information as fast as possible to as remote places as possible. With the use of satellites and unmanned high-altitude platforms as base stations for telecommunication, local solutions to protect radio astronomy in radio quiet zones are becoming less effective. In addition, industry starts to use hitherto unused frequencies in the mm- and sub-mm regime. With the increased recent interest in the Moon, even communication on the moon moves into the focus of the industry and regulators.
Highlighting the biggest advances in radio astronomy across the radio frequency spectrum, to identify the most important bands, highlighting and comparing the specific obstacles through radio frequency interference is one aim of the meeting.
In the light of the developments in the radiocommunications sector and the technical advances in radio astronomy a common effort towards a better protection of radio astronomy is required. The first approach to successfully coexist with other users of the radio spectrum is to reduce the impact of radio interference using technical or software mitigation. Software might also help to avoid the unwanted impact of existing sources of interference, like satellites, by predicting the optimal time windows for an observation.
While radio quiet zones might be less effective than they were in the past, schemes to coordinate radio astronomy and other users of the radio spectrum are being discussed, which would require a complex software solution including more communication.
The third path to acquire a better protection of radio astronomy is to request increased protection for our telescopes by addressing national, local, and international regulators. This might include the additional allocation of radio bands to the Radio Astronomy Services (RAS) at the Radiocommunications Sector of the International Telecommunication Union (ITU-R). This, however, requires the update and identification of priority bands particularly important to radio astronomy.
The second aim of the Focus meeting is to get an overview of the future threats to radio astronomy, the contamination of radio bands, and measures to mitigate the contamination. A potential list of priority bands is discussed.
Context
To start with any process to introduce further protection for radio astronomy, a review and update of the official ITU lists of the radio bands most important to radio astronomy is required. While in an ideal world, radio astronomy should not have to make a selection, only a small part of the spectrum can be protected in regulatory processes, and astronomers have to make wise choices which frequency bands these are. The IAU is the authority to provide such a list. The Focus Meeting is not intended to be a standalone event but will be a milestone to reach this goal. The organisers of this Focus Meeting at the IAU General Assembly (IAUGA) in 2024 in Cape Town are aiming to initiate a dialogue between astronomers and spectrum managers well ahead of the General Assembly. Results of discussions towards this goal can be summarised, and further input will be collected and a strategy towards the World Radiocommunication Conference in 2027 will be developed, where the ambitious goal to achieve more regulatory protection for radio astronomy at an international level can earliest be addressed.
A more detailed background regarding regulatory protection of radio astronomy
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.
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. Complementary protection zones enforced by national authorities may mitigate the RFI situation around observatories, in addition to soft- and hardware RFI excision.
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.
Output
As a first output, the Focus Meeting will create an overview and discussion of recent radio astronomy achievements. Secondly, the astronomical community will be informed about threats to radio astronomy and their background. This important information is often neglected, but now, for once, in the focus of a meeting. Thirdly, the results from preparatory work to this meeting and the meeting outcome will ideally be used to update the information provided by the IAU to regulators, which can directly be used to protect radio astronomy in regulatory processes. It can aid work by the IAU towards a potential resolution to inform and address regulators.
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