|Propagation of Electromagnetic (E-M) Energy and Pulse Volume
The WSR-88D radar transmits a stream or "beam" of energy in discrete
pulses which propagate away from the radar antenna at approximately the
speed of light (~3 X 108ms-1). The volume of each
pulse of energy will determine how many targets are illuminated. This
directly determines how much energy (power) is returned to the radar.
The shape of the radar antenna, the wavelength, , of the energy transmitted, and the length of time the radar transmits determine the shape and volume of each radar pulse.
|The Weather Service Radar-1988 Doppler (WSR-88D) transmits a narrow, conical-shaped beam of pulses with each pulse resembling a truncated cone. The radar pulse volume is illustrated in .
The angular width of the radar beam is defined as that region of
transmitted energy that is bounded by one-half (-3 dB) the maximum
power. The maximum power lies along the beam centerline and decreases
"half-power" points for the WSR-88D result in an angular width of less
than 1°. However, the actual physical width increases with increasing
range (the physical length remains constant) such that the pulse volume
increases with increasing range ().
Since the amount of transmitted power is fixed, a radar pulse's power
density decreases with increasing range. Pulsed transmission also
allows for obtaining target range information.