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Radar Data

Visualization of NEXRAD data.

Visualization of NEXRAD Reflectivity sweeps and derived isosurfaces in Google Earth for the May 22, 2011 Joplin, MO tornado. The image was generated with the NOAA Weather and Climate Toolkit and Google Earth.

Radar, an acronym for radio detection and ranging, is an object-detection system that uses radio waves to determine the range, altitude, direction of movement, and speed of objects. The antenna transmits pulses of radio waves or microwaves, which bounce off any object in their path. The object returns a tiny part of the wave's energy to a dish or antenna.

The National Weather Service initially operated Weather Surveillance Radar - 1957 (WSR-57) which was built using World War II technology. This was followed by Weather Surveillance Radars - 1974 (WSR-74) and then Weather Surveillance Radars - 1988, Doppler (WSR-88D) or NEXRAD (Next Generation Radar).

NEXRAD currently comprises 159 sites throughout the United States and select overseas locations. Level II data include the original three meteorological base data quantities: reflectivity, mean radial velocity, and spectrum width, as well as the dual-polarization base data of differential reflectivity, correlation coefficient, and differential phase. From these quantities, computer processing generates numerous meteorological analysis products known as Level III data.

All NEXRAD Level-II data are available through NCDC. Data are collected and recorded in units of files, which typically contain four, five, six, or ten minutes of base data depending on the volume coverage pattern. There are 41 Level-III products routinely available from NCDC, including precipitation estimates, storm relative velocity, and echo tops.