Pulsed Radar
Pulse Length
Weather radars broadcast a brief intense pulse of energy followed by a relatively long listening period during which the very weak signal reflected from targets is received and processed. The actual pulse transmission time for conventional weather radars is four microseconds or less, and the period between pulses is of the order of 1 millisecond.
Using “pulsed” radar allows many measurements to be obtained for each bin.
In addition, averaging reduces measurement errors with noise.
Random events will not occur in every pulse, but real signals will thus reducing the impact of random echoes.
Definition of a pulse length
The radar returns from precipitation are essentially varying rapidly in time and space. So how long should we illuminate a target with the radar beam to get a realistic estimate of reflectivity?
Using a rapidly pulsed radar to get several samples of reflectivity from each target reduces errors with respect to fluctuations in time and space and reduces the effects of background noise as random events will not occur in every pulse, but real signals will.
The radar transmits a stream or "beam" of energy in discrete pulses which propagate away from the radar antenna at approximately the speed of light (~3x108m/s). 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 beamwidth of the radar antenna and the length of time the radar transmits determine the shape and volume of each radar pulse.
PRF = Pulse Repetition Frequency (Hertz). The rate at which pulses are broadcast.
PRT = Pulse Repetition Time (sec) = time between pulses = 1/PRF. The
time between pulses. For example the Grafton Radar in NSW, Australia:
Pulse length = 2 μS, PRT = 4 ms (PRF = 250 Hz)
Listening time = 3998 μS = 1999 * pulse width.