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Weather Radar Technology: Beyond Nexrad
mitter configuration) offer enough advantages over high-voltage tube amplifiers to justify their inherent waveform constraints. Second, a political and economic debate continues between the communications industries (wireless and satellite radio) and the federal government regarding frequency allocation issues. It is clear today that future generations of mobile communication will apply pressure for expanded use of the existing S-band (10-cm) spectrum now used by groundbased weather and aviation radars. These potential revised spectrum allocations could limit or preclude radar operation in any of our existing “weather bands,” in particular the low-attenuation S-band.
Retaining the allocation of weather radar frequencies, particularly at S-band wavelengths with their relatively small attenuation in heavy rainfall, is critically important to maintaining the operational integrity of the NEXRAD radar system as well as preserving its capabilities for any future replacement system. Furthermore, an important advancement in the replacement system should be realization of more rapid volumetric sampling rate. This will most likely require use of radar waveforms that employ wider bandwidth than the current NEXRAD system. These frequency allocations are continuously being scrutinized for possible real-location to other sectors of society to meet increasing spectrum demands for communications and entertainment applications. The issue is international in scope, since many spectral-use applications extend beyond national borders. Regarding the latter, the International Telecommunications Union sponsors the World Radio Committee (WRC) meeting in Geneva every two years to discuss and decide on spectrum allocation issues. Thus, in addition to preserving these national allocations, U.S. representatives to the WRC meeting must constantly remain alert in order to preserve the global weather radar spectrum allocations (McGinnis, 2001). The importance and value of weather radar to society has been aptly demonstrated with the NEXRAD system, especially through its utility for providing critical warning of severe weather, monitoring precipitation, and helping ensure safe and efficient operation of the National Airspace System (NAS).
The present weather radar users—e.g., the NWS, the FAA and the DoD— must make convincing arguments to spectrum allocation authorities to preserve the S-band region for weather activities necessary to aviation safety, preservation of life and property, and even national security, especially in light of the current world terrorist threat. These arguments can most readily be based on the ability of the longer-wavelength S-band radar systems to penetrate heavy precipitation and allow the proper interpretation of hydrometeor scattering without the complications that arise when the hydrometeor sizes are large relative to the radar wavelength.