IN FOCUS: Supporting Frequency Allocations in Remote Sensing

By Joanne Van Voorhis

Remote sensing instruments rely on the availability of specific, interference-free frequency bands to measure environmental parameters like sea surface temperature, soil moisture, and atmospheric composition. Without proper frequency protection, data from satellites and ground-based systems could be degraded or lost due to radio frequency interference (RFI) from other systems.

The process of regulating the use of the radio frequency spectrum to achieve an efficient use of it is called spectrum management. The Frequency Allocations in Remote Sensing (FARS) Technical Committee (TC) takes an active role in interfacing between the remote sensing community, represented by GRSS, and the broader spectrum management community. Its mission is to safeguard access to the radio-frequency spectrum essential for remote sensing applications.

Why Frequency Management Matters

“The radio frequency spectrum is a resource used by many services and applications…with microwave remote sensing being just one of them, and the demand on the spectrum – especially by telecommunications systems – is growing” explains the FARS TC Chair, Paolo de Matthaeis, Senior Research Engineer at NASA Goddard Space Flight Center. “Coexistence of these systems requires careful coordination in order to avoid interference,” he adds. 

Interference to microwave remote sensing instruments can take a few different forms: strong interference could lead to a complete loss of important measurements, medium interference can significantly degrade data, and even weak interference, which may be hard to detect, can produce small errors in measurement that can have dramatic impacts on data output.

Avoiding Interference Through Frequency Allocation

The radio frequency spectrum is the portion of the electromagnetic spectrum ranging from about 3 Hz to 3 THz, and it is a critical resource for all forms of wireless communication and sensing. To ensure its efficient and interference-free use, the spectrum is divided into distinct frequency bands, each of which is allocated for specific types of radio services by national and international regulatory bodies, such as the International Telecommunication Union (ITU). In some cases a band has a single use and in others, bands are shared.

Broad Outreach and Collaboration

The FARS TC essentially acts as an interface between the remote sensing scientists and engineers and national and international regulators, providing information and resources to help ensure that radio band allocation is protected to help eliminate risk of interference in data. The Technical Committee supports a wide range of efforts to achieve these goals.

Education is key, and the FARS TC works to help educate the remote sensing community about spectrum management frameworks, regulatory processes, and emerging challenges related to frequency allocations and interference. They also promote the development and implementation of radio frequency interference (RFI) detection and mitigation technologies, which are increasingly critical for maintaining data integrity in passive and active sensing systems.

As part of its outreach initiatives, the FARS TC also works to encourage interdisciplinary collaboration among researchers and professionals in remote sensing, radio astronomy, telecommunications, and related fields, with the shared goal of minimizing harmful interference and promoting spectrum coexistence.

Representing GRSS on the Global Stage

“A major component of FARS activities is offering a range of technical sessions, workshops, and panels at major conferences and scientific forums to share information on spectrum policy, regulatory issues, and advancements in interference mitigation strategies” de Matthaeis explains. For example, at every IGARSS, the FARS TC organizes a special invited session on Radio Frequency in Microwave Remote Sensing with presentations on interference detection and mitigation techniques for both passive and active remote sensing. Other conferences in which the Technical Committee regularly participates are the meetings of the Union of Radio Science International (URSI), and at the Annual Meeting of the American Meteorological Society. In addition, the FARS TC annually presents a summary of its activities at the Spring Meeting of the Committee on Radio Frequencies (CORF) of the US National Academies.

Contributing to Regulatory Guidance and Adherence

The FARS Technical Committee plays a role in providing technical input and expert guidance to spectrum managers and regulatory bodies, so that the needs and perspectives of the remote sensing engineering community are well represented in national and international policy discussions. As previously mentioned, regulations on the international use of radio frequency bands are overseen by the ITU, which holds a World Radiocommunication Conference (WRC) every four years to review and update frequency allocations and discuss recommended changes to the Radio Regulations.

The most recent WRC was held in 2023 in Dubai – and the FARS TC is now actively working on some of the WRC 2027 agenda items. Frequency allocations are international agreements and can only be modified during the WRC, so between conferences, proposed changes in regulations are extensively studied, reviewed, and discussed by representatives of national administrations, industry, academia, and other organizations representatives within the Study Groups of the ITU Radiocommunication Sector (ITU-R). In particular, the FARS TC participates in the discussions and meetings of the Working Party (WP) 7C and 3J.

The FARS TC is also involved in the activities of the Space Frequency Coordination Group (SFCG), which is composed of space agencies and other organizations that utilize the radio frequency spectrum for space-based scientific applications. The FARS TC regularly attends and actively participates in the SFCG meetings under GRSS, which has observer status with the SFCG.

“Participation in these meetings is very important for the remote sensing community,” de Matthaeis explains, “because the Technical Committee can advocate for the scientific use of the radio frequency spectrum without having to compromise with commercial interests.”

The Technical Committee also files comments on relevant notices and proposals issued by the US Federal Communications Commission (FCC) that could impact the use of the spectrum for microwave remote sensing.

Technical Tools and Databases

The GRSS FARS TC has also been developing online tools to help the remote sensing community with spectrum allocation and interference issues and raise awareness of the challenges of interference and how regulations are not always followed.

As an example, the GRSS FARS Database of RFI Observations is a collaborative effort led by the FARS Technical Committee. It serves as a centralized repository of RFI events observed in Earth remote sensing data, particularly from passive microwave radiometers onboard satellites. It is publicly accessible and a key resource for understanding and addressing the growing issue of radio-frequency interference. By providing empirical evidence of interference, the database helps inform spectrum managers and regulators about the real-world impact of unauthorized or non-compliant emissions on remote sensing systems.

Contribute to the Efforts of the FARS Technical Committee

The activities of the FARS TC cover many areas of interest and have real impact to help ensure the availability of interference-free frequency bands on which global sensing applications rely. If you would like to play a part in protecting microwave remote sensing from RFI and help ensure that radio spectrum will continue to be available for scientific applications, the Technical Committee welcomes your participation! For more information on the FARS Technical Committee, its initiatives, or membership, visit its webpage and feel free to reach out to the Chair and Co-chairs for more information.