1. Introduction

The American Meteorological Society expresses its concern about the negative impact of the erosion in the radio frequency spectrum allocations for research and operational meteorology due to increasing commercial use. Examples include recent infringements on frequencies allocated to millimeter-wave radars, reductions in radiosonde communication bandwidth, and the recent requirement for sharing of several meteorological satellite bands with commercial users. Protection of the traditional weather-related radio bands is critical for the functioning of and improvements to weather sensing and forecasting, and is therefore in the best interests of public safety and security. The AMS most strongly urges protection of the radio frequencies reserved for operational and research meteorological measurements, and encourages all meteorological users of the radio frequency spectrum to register their uses via their appropriate national channels. It is in all nations’ best interests to protect these frequencies for meteorological use.

The scientific uses of the radio frequency spectrum are expanding as the weather community increasingly moves toward remote sensing for routine weather measurement and prediction. Short-term numerical weather prediction and operational field forecasting increasingly depend on ground-based, active remote sensing systems that are deployed nationally. At the largest scale, many scientific factors push strongly toward improved global weather sensing, which, primarily, is accomplished using passive radiometer systems based on satellites. The effects of short- and long-term climatological changes, such as El Niño or greenhouse gas accumulation, can only be assessed through observations that are global and also have a consistent basis of global calibration. The ability to extend weather forecast skills to include timescales of a week or more requires global observational abilities that are increasingly dependent on remote sensing technology. The variety of remote sensing tools to a ccomplish these varied requirements includes weather radars, profilers, radiometers, and, very importantly, an increasing spectrum of satellite-based measurement systems.

The long-range outlook for increased dependence on passive-satellite remote sensors is based on the global coverage offered by satellite-based weather observing systems, on improvements in technology that open new observational opportunities, and on the need for improved accuracy and resolution in weather measurements. In addition, new satellite and ground-based technologies provide passive measurements of column-integrated liquid water and water vapor in the atmosphere. These measurements are essential to the understanding and improvement of models for the radiative transfer of energy in the atmosphere, an important aspect of climate change.

Current and planned uses of the radio frequency spectrum for passive, radiometric meteorological measurements are illustrated in Table 1, which includes a majority of the passive uses of the radio frequency spectrum for current or planned satellites that provide measurements for meteorological and earth system science studies. The majority of the bands in Table 1 are allocated in full or in part to passive weather measurement needs. The uses of the radio frequency spectrum for passive measurement are changing as new techniques are developed, and in some cases these passive uses of the radio spectrum extend outside formally allocated bands. Many of these passive remote sensing techniques require an uncontaminated background, and in some cases are centered on particular, important molecular lines in the radio frequency spectrum; the requirements for clear allocation of these portions of the radio frequency spectrum are therefore stringent.

Operational weather radar systems provide critical warnings of impending weather events, such as hurricanes at landfall, flash floods, severe storms, precipitation forecasts, and air traffic/weather avoidance support for aircraft. Improved research radar capabilities now provide remote measurement of the type and density of precipitation particles, and may lead to operational aircraft icing measurements in the next decade. Development of satellite-based active remote sensing of the earth is of growing importance. A variety of radar frequencies are used, depending on the application. Table 2 illustrates the most commonly used radio frequencies for active remote sensing of the weather.

Mid- to longer-wavelength radars, operating in frequency bands near 3, 5, and 10 GHz, are principally utilized for observation of precipitating weather systems. Each of these radar frequencies is of important and unique value to operational and/or research measurements of precipitating weather systems. The value of research and operational, satellite-based radar systems for global weather sensing is becoming increasingly clear. Examples include synthetic aperture radar (SAR) systems operating near 5 and 10 GHz that provide earth surface mapping, but also have important oceanographic and atmospheric applications; surface scatterometers operating near 1, 5, and 10 GHz with oceanographic, atmospheric and soil hydrological applications; plus current and planned satellite weather radars operating near 14, 17 and 35 GHz.

Millimeter-wave radars, at 35 and 94 GHz, have unique abilities for sensing of cloud characteristics, and provide measurements that are critical for U.S. and World Meteorological Organization research initiatives relating to the role of clouds in climate. Major research initiatives, including the U.S. Department of Energy, Atmospheric Radiation Program, are planning research utilizing millimeter-wave radars, which will extend over decade-long periods. Millimeter-wave radars are also being studied as a replacement for routine observations of clouds.

Wind-profiling radar systems are an important means for remotely sensing profiles of wind throughout the troposphere and lower stratosphere. Once installed, they operate inexpensively for long periods, providing otherwise unavailable details of atmospheric flow features, plus a way to constrain atmospheric models through data assimilation. Operationally, they provide forecasters a means of identifying wind shifts that are indicative of weather changes and wind shears that pose an aviation hazard. Because different radio frequencies provide coverage of different altitudes in the atmosphere, none of the current wind-profiling frequencies can be eliminated without serious loss to atmospheric research and forecasting.

Radio telemetry of weather data, while not a measurement per se, is essential to meteorological operations and research. It provides the only means of transferring measurements from radiosondes and satellite weather sensors to the ground. It is often is often the best means of transferring surface measurements from remote sites to central data analysis networks. Because of the large investment in radio telemetry systems and the generally limited resources for changing radio equipment, commercialization of the government frequency bands in which this communication takes place should be approached with great caution.

The present concern is multifaceted. Burgeoning communications needs have made the radio frequency spectrum an extremely valuable commodity, and the radio bands required for research and operational needs are in increasing jeopardy. Retention of these radio bands is critical for the continued functioning of and ongoing improvements to operational and research weather sensing. Protection of these traditional weather-related radio bands is in the interest of public safety and security, and is required for improvements in the measurements needed for meteorological operations and research. The AMS most strongly urges protection of the radio frequencies reserved for operational and research meteorological measurements, and encourages all meteorological users of the radio frequency spectrum to register their uses via their appropriate national channels.