as to the private sector and the public. Crum and Alberty (1993) summarize the timeline for the creation of this system, beginning with the establishment of the Joint Doppler Operational Project at the National Severe Storms Laboratory (NSSL) in 1977, proceeding through the award of competitive pre-production contracts to Raytheon and Unisys in the period from 1983 to 1989, followed by the award of a full-scale production contract to Unisys in 1990. The system was deployed as a joint program between the Departments of Commerce, Transportation, and Defense (DOD) during the early to mid-1990’s as a replacement for the 1957 (WSR-57) and 1974 (WSR-74) predecessor radar networks. The National Research Council (NRC, 1995) evaluated coverage of the NEXRAD system in comparison to that of the predecessor systems.
The Terminal Doppler Weather Radar (TDWR) network comprises 45 Doppler weather radars deployed at major commercial airports near medium-to-large-sized US cities with greatest wind-shear risk. This system addresses the FAA’s requirement for surveillance of weather close to airports with higher sensitivity and faster updates than can be provided by the WSR-88D system (Whiton et al., 1998). The TDWR system was developed in the late 1980s after low-altitude wind shear events caused a series of commercial aircraft accidents. It operates at C-band to avoid interference with the ASR radars, the WSR-88D, and other systems operating in the 2.7 - 2.9 GHz band. The system was manufactured by Raytheon on the basis of specifications developed by the FAA, Lincoln Laboratory, and the National Center for Atmospheric Research (NCAR).