Radio astronomy detects extremely faint cosmic radio signals and so is very susceptible to unwanted ‘noise’ created by local sources such as aircraft, satellites and electrical devices including computers, radios, TVs and mobile phones. Radio astronomers call this noise ‘radio frequency interference’, or RFI.

RFI makes it hard to detect faint signals from natural sources in space, requiring additional effort to interpret and distinguish the radiation from cosmological sources, or – in the worst case – masking them completely. As a result, it is important that the radio frequency environment near radio astronomy telescopes is carefully controlled.

We work across five key areas to protect and manage the environments in which our telescopes operate to minimise the impact of RFI on scientific observations.

Spectrum regulation

The radio spectrum is regulated internationally by the International Telecommunications Union – Radiocommunications Sector (ITU-R), a specialised agency of the United Nations, which allocates spectrum to the many radio telecommunications services including the radio astronomy service. This spectrum is then managed at the national level by national regulators. In Australia, the regulator is the Australian Communications and Media Authority (ACMA).

Radio spectrum protection is critical to ATNF operations. We  have been strongly involved in both national and international radio spectrum regulation activities such as those of the ITU-R and the ACMA for over 50 years.

Bodies with responsibility for spectrum regulation and radio astronomy advocacy groups include:

Asia Pacific

• APT – Asia-Pacific Telecommunity
• PTC – Pacific Telecommunications Council
• RAFCAP – Radio Astronomy Frequency Committee in the Asia-Pacific

Europe

• CEPT – European Conference of Postal and Telecommunications Administrations
• CRAF – Committee on Radio Astronomy Frequencies

Americas

• CITEL – Inter-American Conference on Telecommunications
• CORF – Committee on Radio Frequencies (USA)

International

• ITU – International Telecommunication Union
• IAU – International Astronomical Union
• IUCAF – Scientific Committee on the Allocation of Frequencies for Radio Astronomy and Space Science
• SFCG – Space Frequency Coordination Group
• URSI – Union Radio Scientifique International

Local protections

Our telescopes are in regional and remote locations with relatively low population density, often surrounded by low hills, to avoid sources of ground-based interference. These sites are supported by legislative instruments that provide additional protection for the sites from RFI.

Inyarrimanha Ilgari Bundara, our Murchison Radio-astronomy Observatory, is located on Wajarri Yamaji Country in the remote Mid West region of Western Australia. It is home to our ASKAP telescope, as well as other instruments including the SKA-Low and MWA telescopes. To protect this unique radio astronomy site from RFI, the Australian and Western Australian Governments have established the legislated ‘Australian Radio Quiet Zone Western Australia’, forming the world’s largest radio sanctuary for science. ACMA’s Radiocommunications Assignment and Licensing Instruction (RALI) MS32 details coordination of transmitters and receivers in the radio quiet zone.

Additionally, ACMA’s Radiocommunications Assignment and Licensing Instruction (RALI) MS31 acknowledges ‘radio-sensitive zones’ around Australian radio astronomy facilities and protects these from interference when new transmitters are planned or installed in the area. This protection applies to our instruments in eastern Australia including Murriyang, our Parkes radio telescope, as well as our ATCA and Mopra instruments, as well as the University of Tasmania’s Hobart and Ceduna radio telescopes and the Canberra Deep Space Communication Complex (CDSCC), which CSIRO operates on NASA’s behalf.

Mitigation activities

To reduce the impact of RFI on data collected by our telescopes we’ve developed software and methods to filter out signals at frequencies associated with known sources of interference. These methods include ‘beam nulling’ interference from satellites and ‘high-cadence data excision’ from data sets. In addition, we actively schedule observations for our ASKAP telescope so that if interference is detected the telescope moves to observe sources at frequencies less affected.

Monitoring and measurement activities

Cross-checking observations with potential sources of RFI helps astronomers to explain noise or unexpected signals. We undertake active monitoring at our sites using dedicated receivers for monitoring interference and participate in research to characterise unintended emissions from satellites and aeroplanes. We make this data available to astronomers to enable cross-checking with the frequency and timing of known sources of interference.

Collaboration activities

We are working with satellite and mobile telecommunications operators to minimise interference to radio astronomy. One outcome of this collaboration has been the development of an operational data sharing system, used by participating satellite providers to adjust their transmissions to minimise interference when their satellites are passing within the radio horizon of radio astronomy observatories.