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Radar Studies
 

GOALS: to understand  flight patterns and pathways of birds, using RADAR technology

WHAT IS RADAR?

     The word "radar" is an acronym derived from the words RAdio Detection And Ranging. It refers to the technique of using radio waves to detect the presence of objects in the atmosphere. Radar was designed shortly before World War II. Its primary purpose was to detect the presence of aircraft. Today, radar is used for a wide array of applications, but primarily to detect precipitation and other meteorological events.

     NEXRAD is short for NEXt generation RADar and refers to the nationwide network of Doppler radar sites installed by the National Oceanographic and Atmospheric Administration (NOAA). Its official designation is WSR-88D (WSR88D = Weather Surveillance Radar - 1988 - Doppler). NOAA designed this network specifically to provide comprehensive radar coverage of meteorological events occurring in the United States.
     An extensive network of NEXRAD stations provides almost complete radar coverage of the continental United States, Alaska, and Hawaii. The range of each NEXRAD is 124 nautical miles.

 

HOW NEXRAD SEES THE ATMOSPHERE

     NEXRAD has greatly improved the detection of meteorologic events such as thunderstorms, tornadoes and hurricanes. When rain, snow, or hail intercepts a radar's EM pulses, they can scatter considerable amounts of energy. The amounts of returned energy, an indication of the density of targets, and the location of the targets reflecting the energy, are used to assemble a radar image.
     Below is a NEXRAD "base reflectivity" image from 20 Sept. 2001 at 2259 EDT (21 Sept., 2001 Greenwich Mean Time [GMT]). The image shows extensive precipitation in eastern PA, NW NJ, Long Island and southern NY. The location of the colored radar echoes indicates where the rain is in the atmosphere, and the various colors indicate rain density. 
     Target density, in this case, rain density, is measured in decibels (dBZ), a relative scale used to represent other forms of wave energy, like sound. The color scale and corresponding dBZ values are shown in the information bar on the right side of the image. 
     Regions of light and dark blue (5-10 dBZ) show areas of lighter precipitation, while areas of orange and red (45-50 dBZ) are strong, to occasionally severe thunderstorms.
     The image has a "blocky," irregular appearance, typical of precipitation. Also, notice the rapid changes in reflectance values over short distances. This is characteristic of rain events, especially when they contain embedded thunderstorms.