CRAF Case Study

Keeping the frequency bands used by radio astronomy and space sciences free from interference


About The Committee on Radio Astronomy Frequencies (CRAF)

The Committee on Radio Astronomy Frequencies (CRAF) is an ESF Expert Committee that acts on radio frequency issues for European radio astronomy and related sciences on behalf of its Member Institutions in 20 countries.

CRAF provides a cost effective, single European voice on frequency protection issues for the Radio Astronomy Service, achieving a significantly greater impact than that achievable by individual institutions.

CRAF was established in 1987, and the next year it obtained the status of ESF Expert Committee. A strong point of CRAF - compared to similar committees serving other regions in the world - is that CRAF employs a full-time Spectrum Manager to pursue the CRAF mission on an international level.

The mission of CRAF is: 

  • to keep the frequency bands used for radio astronomical observations free from interference;
  • to argue the scientific needs of the European research community for continued access to, and availability of, the radio spectrum for radio astronomy;
  • to support related science communities in their needs concerning interference-free radio frequency bands for passive, non-commercial use.

The operation of CRAF is supported by the annual financial contributions of its Member Institutions across Europe. Its Member Institutions are involved in radio astronomy, i.e., non-commercial scientific research into the passive/non-emitting use of the radio spectrum.

The Challenge

With the rapid development of technology, it becomes increasingly challenging to harmonise the use of the entire radio frequency spectrum among all radio services. 

One of the biggest challenges for CRAF is to be able to protect all frequency bands allocated to radio astronomy for all radio telescopes across Europe - against interference caused by all industrial and commercial transmitting radio devices. 

Radio astronomers use no radio transmitters. Instead, they use incredibly sensitive receivers meant to detect extremely weak signals from remote parts of the Universe. The need for extreme sensitivity makes radio telescopes very vulnerable to interference due to radio signals emitted by man-made devices. The damaging effects of such interference ranges from a radio astronomy band becoming unusable, when man-made transmissions dominate astronomical signals, to hardware burnout caused by excessive transmission power.

The solution

To protect radio astronomy observations, CRAF has to keep an active eye on all potential threats from other emitting users of the radio spectrum. CRAF has to be present at all radio spectrum management meetings concerning these issues, at national, European and global level. 

An essential element is the performance of compatibility studies, which evaluate the interference level expected from proposed new frequency allocations. For operations in the vicinity of radio telescopes, the representatives of CRAF Member Institutions perform compatibility studies and notify their national spectrum management administration of the outcomes. 

At a European and global level, the full-time CRAF Frequency Manager performs such studies and contributes to the drafting of compatibility study reports and policy documents for relevant meetings. The Frequency Manager also serves as the point of contact between astronomers and administrations, and industry nationally, regionally and globally.

The results

CRAF is engaged in two main streams of activities. One is preparation for the World Radio Conference (WRC) of the International Telecommunication Union (ITU), a global four-week-long conference, which takes place every 3 to 4 years. 

At WRCs, the global radio regulations of the ITU are reviewed and revised, based on proposed new spectrum allocations. In the time between conferences, CRAF follows the development of relevant agenda items containing proposals for new frequency allocations. It seeks to incorporateradio astronomy protection criteria from a European perspective. CRAF does so by seeking support from national administrations and helping them to draft resolutions and recommendations for presentation at the Conference.

The WRC held in 2015 (WRC-15) was particularly successful for CRAF. One of the agenda items dealt with a proposal from international mobile telecommunication (IMT) operators to allocate a wide range of frequency bands, including a few allocated to radio astronomy. None of the radio astronomy bands were allocated to the IMT. CRAF led the compatibility studies and chaired the preparatory working group on radio astronomy issues. 

In another agenda item, frequency bands important to radio astronomy were requested for the mobile satellite service (MSS). With CRAF’s help, the European position was successful in opposing this proposal and no new allocation was made to the MSS. CRAF helped the European administrations draft a recommendation that was successfully incorporated into the radio regulations – this includes a list of radio astronomy stations that will not be illuminated by synthetic aperture radars (SAR), except with advance coordination. Such radars can cause radio telescope receivers to burn out. 

For the agenda item on short-range surveillance radars, CRAF helped with drafting a resolution that urges administrations to perform compatibility studies with radio astronomy before employing new radar applications in the newly allocated band.

CRAF’s other field of activity is dealing with new radio applications and devices seeking to use the frequencies already allocated to their corresponding service. Of continued concern to CRAF is the Iridium satellite system that has been causing detrimental interference into a radio astronomy band since it started operation 18 years ago. 

CRAF has been heavily involved in discussions with administrations, asking them to urge Iridium to comply with the radio regulations, as per the Framework Agreement on the protection of radio astronomy observations in Europe signed in 1998 between Iridium and ESF.

Iridium plans to replace its old satellites with a completely new constellation, and has promised to implement a way for its new satellites to protect radio astronomy. However, it has not yet been proven that the method will work. This issue is still the subject of heavy debate and discussion.

CRAF has also recently dealt with wind turbines, surveillance radars on board helicopters, and mobile applications other than IMT. In each case, CRAF has contributed to reports on compatibility studies.

The long-term benefits that the radio astronomy community gains from CRAF activities include the appreciation by the administrations of the need to protect their national radio observatories. They also include the incorporation of protection criteria for radio astronomy observations in all regulatory documents concerning new spectrum allocations posing a potential threat, in particular at the European and global level.

It is hard to estimate monetary aspects directly, but it seems clear that without CRAF's efforts, the continued use of the huge European radio astronomy infrastructures (radio observatories) would become restrictive and suboptimal.

Furthermore, radio observatories that invest a significant part of their annual budget on developing new receivers will suffer a huge loss if it turns out that, after the development phase, the targeted frequency band is no longer accessible due to new industrial usage. CRAF defends the radio astronomy community from such unfavourable outcomes.