WRC-23: Technical preparations for science services

By John Zuzek, Chairman, ITU-R Study Group 7

In the ITU Radiocommunication Sector (ITU-R – one of three Sectors of the International Telecommunication Union), Study Group 7 deals with the radio services supporting scientific pursuits. The group’s technical work is divided among four working parties, 7A, 7B, 7C and 7D, each developing technical documentation in preparation for the World Radiocommunication Conference 2023 (WRC‑23).

Study Group 7’s technical studies will help national administrations formulate positions ahead of the conference, whose outcomes will shape critical systems for our everyday lives on Earth and lay the groundwork for exploring our solar system and studying the universe.

Three new topics on the WRC‑23 agenda relate directly to space science services, while two more topics fall under agenda item 9.1, on the activities of the Radiocommunication Sector since WRC-19.

Agenda item 1.12

This item considers a possible secondary allocation to EESS (active) – the Earth exploration‑satellite service (active) – or for use by radar sounders that would operate around 45 megahertz (MHz).

Those frequencies around 45 MHz are under consideration for space-based active remote sensing of the Earth’s surface, both to detect water tables and to measure ice thickness in polar regions. Working Party 7C has been studying these possibilities since prior to 2015.

1.12: Radar sounders around 45 MHz

Issue: Space-based active sensing could help detect water tables below ground and assess ice thickness in polar regions.

The first studies established technical and operational characteristics for the radar sounders to be used in compatibility studies with other radiocommunication services, resulting in Recommendation ITU‑R RS-2042‑1. Spaceborne active sensors, including radar sounders that are under consideration in this agenda item, can only obtain repetitive measurements of subsurface water deposits, which are crucial for these studies, from desert environments like North Africa and the Arabian Peninsula, or from ice sheets in such areas as Greenland and Antarctica (illustrated on previous page).

More recent studies have focused on compatibility, looking at how to protect incumbent radiocommunication services while a radar sounder is operating.

Agenda item 1.13

This item considers a possible upgrade of the allocation to space research in the frequency band 14.8‑15.35 gigahertz (GHz), which is currently a global secondary allocation.

1.13: Possible primary upgrade of the space research service in the 14.8-15.35 GHz frequency band

Issue: Current space research links to data relay satellite are on a secondary basis, while future systems also require use of this band.

Working Party 7B’s studies aim to determine the operating characteristics that would allow the space research service in this band to operate on a co-primary basis with existing primary allocations. This would open up the band for a variety of space research activities within 2 million kilometres from Earth, including exploration missions to or around the Moon.

Systems under consideration include direct data downlinks from spacecraft to earth stations, Earth‑to‑space links to data relay satellites, and space‑to‑space links from spacecraft to data relay satellites.

Agenda item 1.14

This item calls for reviewing existing and possible new primary frequency allocations to the EESS (passive) in the frequency range 231.5‑252 GHz, ensuring they align with up-to-date requirements for passive remote sensing observation.

1.14: Adjustments to EESS (passive) allocations in the 231.5-252 GHz frequency band

Issue: Envisioned remote sensing operations need to be compatible with scientific needs.

Allocations above 71 GHz were adjusted in 2000 when less was known about requirements in this range. Current usage has been limited to instruments for microwave limb sounding, which point towards the Earth’s limb (the edge of the atmosphere) and are unaffected by interference from terrestrial sources.

Spurred by new observation requirements for studying cloud ice, the proposed passive system uses conical scanning sensors pointed at clouds above the surface of the Earth. Ice clouds, covering more than 33 per cent of the Earth’s surface, greatly affect the climate and hydrological cycle, including precipitation, atmospheric structure, and cloud processes.

Global measurements are urgently needed of ice cloud properties. Although no terrestrial services are currently deployed in the 231.5‑252 GHz frequency range, technical studies under Working Party 7C focused on how to avoid incompatibilities when such deployments happen.

Agenda item 9.1 a)

This item considers the protection and possible recognition of radio spectrum‑reliant space weather sensors that help to predict and warn about global risks.

9.1 a): Space weather

Issue: Space weather sensors await regulatory recognition.

Space weather systems are used to observe solar activity such as coronal mass ejections (CME), geomagnetic storms, solar radiation, and solar winds, along with other phenomena in space that can affect our activities on or around Earth.

Working Party 7C has focused on identifying space weather sensors and the radio spectrum in which they operate. These systems are currently deployed in a few locations for global observation, with involvement by numerous countries and institutions, and operate relatively free of harmful interference.

But changes in the Radio Regulations could change the future radio interference environment. Sensors monitoring low-level natural solar or atmospheric emissions can be very sensitive to harmful interference.

Working Party 7C has also proposed a possible definition for space weather.

Agenda item 9.1 d)

This item considers how to protect passive remote sensing systems in frequency band 36‑37 GHz, in the EESS (passive) sensing channel, from emissions of non-geostationary (non‑GSO) fixed-satellite service (FSS) satellites. This was a matter not fully resolved under WRC‑19 agenda item 1.6.

9.1 d): EESS (passive) in the 36-37 GHz frequency band

Issue: EESS (passive) service in the frequency band needs protection from non‑GSO FSS space stations

Since then, Working Party 7C has studied two potential interference scenarios from non‑GSO FSS systems operating in 37.5‑38 GHz: interference into the sensing channel of EESS (passive) from non‑GSO FSS constellations operating at a lower altitude than EESS (passive) sensors; and interference into the cold calibration channel of EESS (passive) from non‑GSO FSS constellations operating at a higher altitude than EESS (passive) sensors.

The results of these studies are summarized in a text to be considered at the Conference Preparatory Meeting (CPM), ahead of WRC-23.

Definition of reference time scale

Resolution 655 (WRC‑15), concerning the definition of the international reference time scale and the dissemination of time signals via radiocommunication systems, required ITU-R to strengthen cooperation with the International Bureau of Weights and Measures (BIPM) and report study results on reference time scales.

The first part of this work was completed in June 2020 with a Memorandum of Understanding between ITU‑R and BIPM. Working Party 7A completed the second part in October 2022 with the approval of Report ITU‑R TF.2511‑0 – Content and structure of time signals to be disseminated by radiocommunication systems and various aspects of current and potential future reference time scales, including their impacts and applications in radiocommunication.

Potential interference with science services

Several WRC-23 agenda items are of concern for science services. Working Parties 7B, 7C and 7D have sought to ensure that any impacts on science services are fully considered, with technical studies looking at either in-band or adjacent band compatibility with other radiocommunication services.

Agenda items of concern

1.2:       International Mobile Telecommunications
1.4:       Use of high-altitude platforms
1.6:       Radiocommunications for sub-orbital vehicles
1.10:     Non-safety aeronautical mobile applications
1.16:     Earth stations in motion
1.17:     Satellite-to-satellite links
1.18:     Mobile satellite service
1.19:     Fixed satellite service (space-to-Earth)

Safeguarding and enhancing science services

WRC‑23 decisions will affect the science services directly.

Allocating spectrum near 45 MHz for space radar sounders should enable us to monitor polar ice thickness and detect aquifers in desert areas.

Rearranging 231.5‑252 GHz allocations would greatly enhance our ability to make global ice-cloud measurements while safeguarding atmospheric measurement through microwave limb sounding.

Upgrading the secondary space research allocation in 14.8‑15.35 GHz can enhance our ability to send Moon missions and explore space in our immediate vicinity.

Finally, by defining space weather and continuing studies in this field with a WRC‑27 agenda item, we can ensure the protection of critical space weather sensors (see figure) and systems for the future.

This article first appeared in the ITU News Magazine, which outlines key technical and regional perspectives on topics to be discussed at the World Radiocommunication Conference (WRC-23) taking place in Dubai, UAE, between 20 November and 15 December.

Header image credit: Hellen Vanessa de Carvalho Silva