Many of the benefits of today’s advanced technology are possible due to critical use of radio signals sent from orbiting satellites, such as GPS and the government’s weather satellites.
The devastating 2017 Atlantic hurricane season set records for the number of consecutive hurricanes and overall damage costs. Therefore, it is an appropriate time to reflect on our dependence on forecasters and emergency responders to save lives in the face of violent weather. These professionals rely upon signals from both GPS and NOAA’s Geostationary Operational Environmental Satellites (GOES) which provide position, timing, and weather data directly to end users across the United States.
GPS signals enabled first responders and private citizens to make hundreds of rescues while GOES satellites transmitted vital data for weather and flood prediction, including stunning imagery of Hurricanes Harvey, Irma and Maria.
To aid in tracking major storms, hurricane hunter aircraft deploy radiosondes that descend directly into the violent conditions below, providing wind speed and direction, and determining their position using GPS.
The American public’s dependence on signals from GOES satellites does not go away once a hurricane has come ashore and dissipated. After Hurricane Harvey, Federal and Texas officials used GOES-relayed data for many days to determine when to release water from overflowing Houston-area reservoirs.
GPS applications are not limited to these emergency situations. Farmers now use high-precision GPS guidance in all phases of food production, from planting, through harvest. These innovations have dramatically increased crop yields while greatly reducing the use of fertilizer and herbicides. These precision GPS techniques have revolutionized farming, with great benefits to farmers, consumers, and the environment.
Unfortunately, reliable access to the satellite signals from GPS and GOES satellites are now jeopardized by increasing demands for radio spectrum for terrestrial wireless systems, including the ubiquitous cell towers that will provide the next iteration of services. Commercial interests have requested to share the spectrum bands in or near these critical functions. Today, users receiving GPS and downlinks from GOES do not have to compete with terrestrial signals that can overpower the much weaker signals arriving from satellites many miles above. That may be about to change. Asking satellite receiving stations to work in the presence of cell towers at nearly the same frequency is like asking someone to hear a whisper in the middle of a rock concert.
The enormous demand for spectrum has driven regulators to consider placing fundamentally different uses of radio spectrum – like GPS and cell towers – next to each other in frequency bands that have never been used this way before. Without careful consideration of how to account for vastly different types of users, such proposals can have unintended consequences.
The stakes for adding new terrestrial radio services in the frequencies near GPS and GOES – known collectively as “L-band,” from approximately 1500 – 1695 megahertz – are high. Preventing interference to these existing satellite-based radio services is critical to millions of Americans.
Any new applicant for services in this vital spectrum will need to make a strong case for how both current critical services and new uses can coexist. Service disruption or performance degradation to satellite-based position, timing, weather or water uses can have severe consequences. Decision makers should carefully consider the public safety and economic aspects of any regulatory changes that might affect satellite-based services such as GPS and GOES.
Thomas Powell is the principal director of user systems at The Aerospace Corporation. David Lubar is a senior project engineer for the Systems Development, Operations and Protection Directorate at The Aerospace Corporation. Karen L. Jones is a senior project leader with the Center for Space Policy and Strategy at The Aerospace Corporation. All are authors of the newly published report from the Center titled “Bracing for Impact: Terrestrial Radio Interference to Satellite-Based Services.”
