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DLOC Principles of Meteorological Doppler Radar:
WSR-88D Fundamentals

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Next Page: Pulse Duration

Listening Period

If PRT is the time from the beginning of one pulse to the beginning of the next pulse, and t is the time actually spent transmitting, then PRT-t = greek symbol tau is the listening period. For example, in Figure 5, if the WSR-88D is operating in one of the short pulse modes (VCP 11, 12, 21, 121, 211, 212, 221, or 32) and using a PRT of 1000 µsec (0.001 s or 1 millisecond), then the listening period is greek symbol tau = PRT- t = 1000 - 1.57 µsec = 998.43 µsec (or 0.99843 millisecond). As a result, for each hour the radar is active at this PRT, only about 5.7 seconds is spent transmitting. This means that 99.8% of the time the WSR-88D is listening for signal returns. In long pulse, the radar transmits 17.1 seconds every hour, spending 99.5% of its time listening.

Figure 5.  Example of pulse duration and pulse length.

Figure 5: (Click to Enlarge) Example of pulse duration, t, and listening period, greek symbol tau. Time is along the x axis and, when multiplied by the speed of light, c, yields the actual physical length of the pulse, H.

With the dual-polarization upgrade of the WSR-88D, the radar transmits a single pulse with both a horizontal and vertical component. The horizontal and vertical receivers then listen for their respective channels. As a result, the listening period of the WSR-88D doesn't change with the implementation of dual-polarization technology.

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