4

Concluding Remarks

A common thread among the discussions in this report is the need to ensure protection of radio astronomy observations by means beyond frequency-based allocations and prohibitions on transmission. Redshift from the expanding universe moves signals that provide key cosmological fingerprints well outside the bands established for protection of observations of the local universe. Fast radio bursts, observed in broad spectral ranges, are unpredictable and currently unexplained but, as with pulsars, may one day prove to be a key tool for unlocking new knowledge. Making cutting-edge next-generation observations of continuum sources, such as black holes, galaxies, and explosive events, requires access to large bandwidths to reduce noise and maximize sensitivity. Advances along these lines are only possible through interference-free access to a large fraction of the spectrum. As discussed in multiple places in this report, radio quiet zones (RQZs) have been essential tool in attaining such access. Similarly, the emerging framework for “radio dynamic zones,” where dynamic sharing of the radio spectrum between active and passive use is permitted, offers the prospect of such interference free access when needed. However, the rapid increase in airborne and, most notably, spaceborne transmissions, unless carefully considered and regulated, threatens to undermine the hard won and costly efforts to ensure this protection. Thankfully, in many cases, the same beam-steering technologies that enable new spaceborne and airborne services should also be able to ensure the

protection of current and planned radio astronomy service (RAS) assets, including through the steering of “beam nulls” toward RAS facilities. The International Telecommunication Union and administrations need to adopt a regulatory framework that ensures that RAS observations are protected from these new transmissions at least as well as they are from those of incumbent services. Indeed, by supporting efficient spectrum use, the development of the sophisticated spatial and temporal coordination technologies needed to achieve this protection serves the needs of active services as well.

Sensors in the Earth exploration-satellite service (EESS), both active and passive, provide information that is essential for Earth system scientific research, operational forecasting, and decision support. Radio frequency observations provide unique and continually exploited information on Earth’s land, oceans, ice sheets, weather, and ecosystems. In contrast with RAS observations, EESS sensors routinely observe the whole globe, making geographically driven approaches unsuitable for their protection. As Earth system science advances, so to do the needs for more capable, more accurate, and more frequent observations. This will only be possible if interference-free access to passive observations of the entire globe is guaranteed on a continuous basis. Approaches to time-sharing of bands where EESS (both passive and active) shares allocations with other services have been explored in the past. However, despite these efforts, significant interference has remained in such cases. The committee believes that time-sharing does not represent a sustainable approach for protection of the EESS service as the needs and applications for continuous Earth observations grow.

Given advances in optical communication technologies and the large bandwidth they offer, the committee hopes that such systems can increasingly be employed for Earth-to-space, space-to-Earth, and space-to-space links. While optical communication is particularly well suited to the lunar environment—as noted in the committee’s discussion of Agenda Item 1.15—it also has the potential to revolutionize communications to, from, and within the near-Earth environment also. This could relieve pressure on use of the radio spectrum and thus reduce interference into essential and unique passive observations in the RAS and EESS (passive) services.

As discussed, many 2027 and 2031 World Radiocommunication Conference agenda items have the potential to affect scientific use of the radio spectrum, particularly passive observations for radio astronomy and Earth remote sensing. The committee hopes that this report informs those preparing for these meetings of the value of these observations and provides suitable recommendations for their continued protection.