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NEXRAD or Nexrad (Next-Generation Radar) is a network of 160 high-resolution S-band Doppler weather radars operated by the National Weather Service (NWS), an agency of the National Oceanic and Atmospheric Administration (NOAA) within the United States Department of Commerce, the Federal Aviation Administration (FAA) within the Department of Transportation, and the U.S. Air Force within the Department of Defense. Its technical name is WSR-88D, which stands for Weather Surveillance Radar, 1988, Doppler. NEXRAD detects precipitation and atmospheric movement or wind. It returns data which when processed can be displayed in a mosaic map which shows patterns of precipitation and its movement. The radar system operates in two basic modes, selectable by the operator – a slow-scanning clear-air mode for analyzing air movements when there is little or no activity in the area, and a precipitation mode, with a faster scan for tracking active weather. NEXRAD has an increased emphasis on automation, including the use of algorithms and automated volume scans. ==Deployment== In the 1970s, the U.S. Department of Commerce, Department of Defense and Department of Transportation found the need to replace the existing national radar network, consisting of WSR-74 and WSR-57 radars not utilizing Doppler technology that were respectively developed in 1974 and 1957, to better serve their operational needs. The Joint Doppler Operational Project (JDOP) was formed in 1976 at the National Severe Storms Laboratory (NSSL) to study the usefulness of using Doppler radar to identify severe and tornadic thunderstorms. Tests over the next three years, conducted by the National Weather Service and the Air Weather Service agency of the U.S. Air Force, found that Doppler radar provided much improved early detection of severe thunderstorms. A working group that included the JDOP published a paper providing the concepts for the development and operation of a national weather radar network. In 1979, the NEXRAD Joint System Program Office (JSPO) was formed to move forward with the development and deployment of the proposed NEXRAD radar network. That year, the NSSL completed a formal report on developing the NEXRAD system. When the proposal was presented to the Reagan administration, options were considered to build the radar systems: either allowing corporate bids to build the systems based on the schematics of the previously developed prototype radar or seek contractors to build their own systems using predetermined specifications. The JSPO group opted to select a contractor to develop and produce the radars that would be used for the national network. Radar systems developed by Raytheon and Unisys were tested during the 1980s, however it took four years to allow the prospective contractors to develop their proprietary models. Unisys was selected as the contractor, and was awarded a full-scale production contract in January 1990.〔〔 Installation of an operational prototype was completed in the fall of 1990 in Norman, Oklahoma. The first installation of a WSR-88D for operational use in everyday forecasting was in Sterling, Virginia on June 12, 1992. The last system deployed as part of this installation campaign was installed in North Webster, Indiana on August 30, 1997. In 2011, a single new radar was added at Langley Hill, Washington to better cover the Pacific Coast of that area; other radars also filled gaps in coverage at Evansville, Indiana and Ft. Smith, Arkansas following the initial installations. The site locations were strategically chosen to provide the most overlapping coverage between radars in case one failed during a severe weather event. Where possible, they were co-located with NWS Weather Forecast Offices (WFOs) to permit quicker access to maintenance technicians.〔(【引用サイトリンク】url=http://www.economics.noaa.gov/library/documents/benefits_of_weather_and_climate_forecasts/wsr-88d-radar-tornado_warnings_casualties.pdf )〕 The NEXRAD radars incorporated a number of improvements over the radar systems that were previously in use. The new system provided Doppler velocity, improving tornado prediction ability by detecting any rotation present within the storm at different scan angles. It provided improved resolution and sensitivity, allowing operators to see features such as cold fronts, thunderstorm gust fronts, and mesoscale to even storm scale features of thunderstorms that had never been visible on radar. The NEXRAD radars also provided volumetric scans of the atmosphere allowing operators to interrogate the vertical structure of storms and additionally can act as wind profilers in providing detailed wind information for several kilometres above the radar site. The radars also had a much increased range allowing detection of weather features at much greater distances from the radar site.〔(【引用サイトリンク】url=http://sysu1.wsicorp.com/unidata/intro.html )〕 WSR-88D development, maintenance, and training are coordinated by the NEXRAD Radar Operations Center (ROC) located at the National Weather Center (NWC) in Norman, Oklahoma.〔(【引用サイトリンク】url=http://roc.noaa.gov/WSR88D/About.aspx )〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「NEXRAD」の詳細全文を読む スポンサード リンク
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